Grimm, Klaus

Mayr, Herbert

English

Universität München: Elektronischen Publikationen

J. Org. Chem. 1992,57,1057-1059 1067 
The Journal of 
Organic 
Chemistry 
VOLUME 57, NUMBER 4 FEBRUARY 14,1992 
0 Copyright 1992 by the American Chemical Society 
Communications 
Synthesis of Allylazo Compounds by Reactions of Aryldiazonium Salts with Allylsilanes 
Herbert Mayr**t and Klaus Grimm 
Znstitut fur Chemie der Medizinischen Universitdt zu Lubeck, Ratzeburger Allee 160,D-2400 Lubeck, Germany 
Received September 27, 1991 
Summary: Aryldiazonium tetrafluoroborates react with 
allylsilanes to yield allylazo compounds. If the allylic 
carbon attached to the azo group carries hydrogen, tau- 
tomerization with formation of hydrazones takes place. 
The coupling of aryldiazonium ions with arylamines and 
phenols, discovered by Griess in 1858; has been one of the 
most important reactions in industrial chemistry for more 
than a century.2 Among the aliphatic C-nucleophiles 
previously reported to react with diazonium ions, CH- 
acidic compounds,3a enol enamines,3c and 1,3- 
dienmM are the most important ones. Marxmeier and Pfeil 
have found that the 2,4-dinitrobenzenediazonium ion la 
also reacts with ordinary alkenes, often with cleavage of 
the original CC double bond as shown in Scheme I.4 
Though allylsilanes have been combined with a manifold 
of electrophiles: reactions with diazonium ions have not 
yet been reported. Since the nucleophilicity of allyltri- 
methylsilene is similar to that of those alkenes? which are 
known to be susceptible to electrophilic attack by la, the 
electrophilicity of la should also be sufficient for a reaction 
with allylsilanes. 
Combination of the y,y-disubstituted allylsilanes 2a-2g 
with 2,4dinitrobenzenediazonium tetrafluoroborate la in 
acetonitrile givm the a l l y h  compounds 3a-3g in 38-94% 
yields (Table I).’ This reaction thus provides a 
straightforward access to allylazo compounds, which are 
of interest as precursors to allyl radicals! Representatives 
of this class of compounds have previously been synthes- 
ized by treatment of sulfamides (from allylamines and 
N-sulfonylaniline) with NaOCl and NaOHQ or by sigma- 
tropic rearrangements of diazenes, which have been gen- 
erated by oxidation of N-allyl-N-arylhydrazine~.~ 
‘Present address: Institut f k  Organische Chemie der Technis- 
chen Hochschule Darmstadt, Petersenstr. 22, W-6100 Darmstadt, 
Germany. 
OO22-3263/92/ 1957-1057$03.00/0 
Scheme I 
NO, 
NO2 
la 
18 Zh 
0 2 N Q N e N a  r.QN,NO/B 
NO2 NOz 
3h 4h 
The reaction of methallyltrimethylsilane 2h with la BFL 
initially yields the crystalline allylazo compound 3h, which 
(1) Griess, P. Liebigs Ann. Chem. 1868, 106, 123. 
(2) (a) Szele, I.; Zollinger, H. Top. Curr. Chem. 1983, 112, 1. (b) 
Hegarty, A. F. In The Chemistry of Diazonium and Dbzo Groups; Patai, 
S. ,  Ed.; Wiley: Chichestsr, 1978; p 611. (c) Schmdehotte, K. H. Meth- 
oden der Organischen Chemie (Houben- Weyl-Mfiller); Thieme: Stutt- 
part, 1965; Vol. X/3, p 213. (d) Saunders, K. H.; Allen, R. L. M. Aromatic 
Diazo Compounds; Edward Arnold London, 1983. 
(3) (a) Parmerter, S. M. Org. React. 1969,10,1. (b) Terent’ev, A. P.; 
Jagorsvkii, V. A. Zh. Obshch. Khim. 1966, 26, 211. (c) Crary, J. W.; 
Quayle, 0. R.; Lester, C. T. J.  Am. Chem. Soc. 1956,78,5584. (d) Huisgen, 
R.; Bronberger, F. Tetrahedron Lett. 1984, 25, 57. (e) Huisgen, R.; 
Bronberger, F. Tetrahedron Lett. 1984,25,61. 
0 1992 American Chemical Society 
1058 J. Org. Chem., Vol. 57, No. 4, 1992 Communications 
Table I. Allylazo Compounds from y,y-Disubstituted Allylsilanes 2 and 2,4-Dinitrobenzenediaeonium Tetrafluoroborate la  
dylailanes 2 products 3 (% yield) NMR chemical shifts" 
rSiMq 
rSiMe3 
0"""" 
SiMe, v 
&SiMe3 
84 
69 
38b 
59 
41b 
59 
94 
24.46 (q), 74.75 (a), 115.01 (t), 141.32 (d) 
19.68 (q), 24.07 (q), 76.85 (a), 112.79 (t), 147.13 (e) 
23.92 (t), 35.29 (t), 86.53 (a), 115.21 (t), 139.67 (d) 
22.27 (t), 25.60 (t), 33.94 (t), 76.66 (4, 117.06 (t), 140.08 (d) 
22.57 (t), 30.34 (t), 35.90 (t), 80.59 (4, 115.19 (t), 141.34 (d) 
18.51 (t), 25.72 (q), 29.19 (q), 31.25 (91, 36.76 (4, 37.54 (t), 40.60 (t), 77.17 (d, 
111.40 (t), 159.63 ( 8 )  
"Aryl-C C-16 149.96-150.43 (E), C-2 6 = 144.51-144.81 (E), C-3 6 120.24-120.51 (d), C-4 6 = 147.01-147.22 (E), C-5 6 128.30-128.42 
(d), C-6 6 = 120.39-121.05 (d). bUnidentified hydrazones were also formed. 
Scheme I11 
has been stored in the dark at -20 "C for several months. 
At room temperature, rearrangement to the hydrazone 4h 
(4) Marxmeier, H.; Pfeil, E. Chem. Ber. 1964, 97, 53. 
(5) (a) Weber, W. P. Silicon Reagents for Organic Synthesis; 
Springer-Verlag: Berlin, 1983. (b) Schinzer, D. Synthesis 1988,263. (c) 
Fleming, I. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. 
D., Eds.; Pergamon Press: Oxford, 1979 Vol. 3, p 541. (d) Sakurai, H. 
Pure Appl. Chem. 1985, 57, 1759. (e) Colvin, E. Silicon in Organic 
Synthesis; Butterworths: London, 1981. 
(6) (a) Mayr, H.; Schneider, R.; Irrgang, B.; Schade, C. J .  Am. Chem. 
SOC. 1990,112,4459. (b) Mayr, H. Angew. Chem. 1990,102,1415; Angew. 
Chem., h t .  Ed. Engl. 1990,29,1371. (c )  Hagen, G.; Mayr, H. J. Chem. 
SOC., Chem. Commun. 1989,91. (d) Hagen, G.; Mayr, H. J. Am. Chem. 
SOC. 1991,113,4954. 
(7) Typical Procedure. Allylsilane 2b (0.530 g, 2.67 mmol) was added 
to a suspension of 2,4-dinitrobenzenediazonium tetrafluoroborate (0.500 
g, 1.77 mmol) in dry acetonitrile. The mixture was stirred until the 
diazonium salt dissolved. After addition of water, the mixture was ex- 
tracted with two 10-mL portions of CH,Cl,. The organic layers were dried 
over CaCl, and evaporated. After purification of the residue by column 
chromatography (silica gel, CHzClz/pentane, 70/30) product 3b was ob- 
tained and recrystallized from pentane: Orange plates (0.340 g, 69%), 
mp 55-56 'C. 
Table 11. Relative Reactivities of the Allylsilanes 2a-2h 
toward (p-HSCOC6H4)PhCH+ and Their Ability To React 
with Diazonium Ions 
reaction with 
kre? la  lb l c  
2i 1 + - - 
2j 6.60 + - - 
2c -7 + + - 
2d -7 + + - 
2e -7 + + - 
2a 7.92 + + - 
2h 508 + + - 
2f - 103 + + I 
2B - 103 + + + 
2b 1675 + + + 
From ref 6 4  estimates marked by the - sign are baaed on k,, 
values of structurally analogous compounds. 
is detectable after several hours. This tautomerization is 
very fast in chloroform solution (not purified from traces 
of HC1) or during chromatography on silica gel. Analo- 
gously, the reaction of 2i and 2j with la yields the hy- 
drazones 4i and 4j as stable final products. Allylsilanes 
with one or two hydrogen atoms in y-position thus can 
(8) (a) Luedtke, A.; Meng, K.; Timberlake, J. W. Tetrahedron Lett. 
1987,28,4255. (b) Adams, J. S.; Burton, K. A.; Andrew, B. K.; Webman, 
R. B.; Engel, P. S. J. Am. Chem. SOC. 1986, 108, 7935. (c) Roesi, M.; 
Golden, D. M. J. Am. Chem. SOC. 1979,101, 1230. (d) Crawford, R. J.; 
Takagi, K. J. Am. Chem. SOC. 1972, 94, 7406. (e) Crawford, R. J.; 
Hamelin, J.; Strehlke, B. J. Am. Chem. SOC. 1971,93,3810. (0 AI-Sader, 
B. H.; Crawford, R. J. Can. J .  Chem. 1970,48,2745. (g) Porter, N. A.; 
Iloff, P. M. J. Chem. SOC., Chem. Commun. 1971, 1575. 
(9) Baldwin, J. E.; Brown, J. E.; Hbfle, G. J. Am. Chem. SOC. 1971.93, 
788. 
J.  Org. Chem. 1992,57,1059-1061 1059 
oxidatively be desilylated by treatment with aryldiazonium 
ions. 
Preliminary experiments showed that among the allyl- 
silanes used in this work all but 2i and 2j also react with 
the leas electrophilic pnitrobemnediazonium ion lb. The 
highly alkylated allylsilanes 2b and 2g even react with the 
unsubstituted benzenediazonium ion IC to give 3b' and 3g' 
in 51 and 74% yield, respectively. In accord with our 
previous report that allylstannanes are more nucleophilic 
than structurally analogous allylsilanes by several orders 
of magnitude,Bd tri-n-butylprenylstannane also reacted with 
the parent benzenediazonium ion IC to afford 49% of 3a'. 
Though the correlation between reactivities toward car- 
benium and diazonium ions does not seem to be perfect, 
Table I1 shows that the nucleophilicity scale developed 
with respect to diarylcarbenium ionse also allows one to 
roughly predict the feasibility of electrophilic attack of 
diazonium ions at  allylsilanes. 
4 N  0 N? 
l b  IC 
3a' 3b' ON+?? 3g' ON..* O N + N ) +  
Registry No. la, 345-12-0; lb,  456-27-9; IC, 369-57-3; 2a, 
18293-99-7; 2b, 64545-12-6; 2c, 834386843; 2d, 63922-76-9; 2e, 
138061-12-8; 2f, 138061-13-9; 2g, 138061-14-0; 2h, 18292-38-1; 2i, 
762-72-1; 2j, 14579-08-9; 3a, 138061-15-1; 3a', 31928-42-4; 3b, 
138061-16-2; 3b', 138061-17-3; 3c, 138061-18-4; 3d, 138061-19-5; 
3e, 138061-20-8; 3f, 138061-21-9; 3g, 138061-22-0; 3#, 138061-23-1. 
(R)-l-Acetyl-5-isopropoxy-3-pyrrolin-2-one: A Versatile Chiral Dienophile from (S)-Malic Acid 
Wim-Jan Koot, Henk Hiemstra,* and W. Nico Speckamp* 
Department of Organic Chemistry, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands 
Received October 28, 1991 
Summary: The title compound, readily prepared from 
@)-malic acid, reacts as a Diels-Alder dienophile with 
several 1,3-&enes with excellent regio- and stereoselectivity 
without loss of enantiomeric purity. The synthesis of an 
enantiomerically pure intermediate in a projected synthesis 
of gelsemine is detailed. 
Of the various ways to control the absolute stereochem- 
istry of an intermolecular Diels-Alder reaction, the ap- 
proach involving the use of an enantiomerically pure 
dienophile has proven to be most practicable.' In this 
paper we wish to present the synthesis and utility of the 
chiral dienophile (R)-l-acetyl-5-isopropoxy-3-pyrrolin-2-one 
(l), which in essence can be viewed as an enantiomerically 
pure synthetic equivalent of maleimide.2 
Me H ~w&o - acid Hwq@o 
Me 
Me X,.\%.QO E* ,."' *Q0 
OAMe M e A M e  A A 
1 2 3s R = A C  4 
3b R = H  
The choice for the structural features present in 1 was 
eventually made, when we had found that other A3- 
pyrrolin-2-ones such as Z3 were unsuitable for our purposes. 
The isopropoxy function at  C-5 in 1 is meant to direct 
l,&dienes to react at  the opposite face of the molecule to 
give 3ae4 The significance of an alkoxy function at  C-5 
(1) For reviews, see: (a) Paquette, L. A. In Asymmetric Synthesis; 
Morrison, J. D., Ed.; Academic: New York, 1984; Vol. 3, Chapter 7. (b) 
Oppolzer, W. Angew. Chem., Int. Ed. Engl. 1984,23,876. 
(2) For recent alternative approaches, see: (a) Arai, Y.; Matsui, M.; 
Kolzumi, T.; Shiro, M. J. Org. Chem. 1991,56,1983. (b) Baldwin, S. W.; 
Greenspan, P.; Alaimo, C.; McPhail, A. T. Tetrahedron Lett. 1991, 32, 
5877. For a chiral synthetic equivalent for maleic anhydride, see: (c) 
Feringa, B. L.; de Jong, J. C. J. Org. Chem. 1988,53,1125. (d) de Jong, 
J. C.; Janaen, J. F. G. A.; Feringa, B. L. Tetrahedron Lett. 1990,31,3047. 
(3) The study of 2 originated from our work on the synthesis of the 
indole alkaloid peduncularine and will be described in a full paper; see: 
Klaver, W. J.; Hiemetra, H.; Speckamp, W. N. J. Am. Chem. SOC. 1989, 
I1 1 ,  2588. 
0022-326319211957-1059$03.00/0 
Scheme I" 
5 6 7 1 
"Reagenta and conditions: (a) (i) LiBHl (1.0 equiv), THF, -20 - 0 "C, (ii) HzS04 in i-PrOH (pH = 3), 0 "C - reflux, 55%; (b) 
(C13CCO)z0 (1.1 equiv), D W  (1.1 equiv), EhO, -60 "C - rt, 
86%; (c) Ac20/pyridine, DMAP (cat.), 0 O C  - rt, 85%. 
becomes apparent after removal of the N-acetyl function, 
as 3b is expected to allow the introduction of a variety of 
substituents via N-acyliminium intermediate 4.6 The 
presence of the N-acetyl function in 1 is required to pre- 
vent racemization and enhance the reactivity and regio- 
chemical bias of the dienophile? 
The synthesis of (R)-1 is detailed in Scheme I. (S)-3- 
Acetoxysuccinimide (5), readily prepared on large scale 
from (S)-malic acid,' was regioselectively reduced with 
lithium borohydride in THF at -20 OC. The crude reaction 
mixture was acidified with sulfuric acid. The solvent THF 
was then substituted for 2-propanol and the resulting 
mixture heated at  reflux for 18 h to effect both iso- 
propanolysis and transesterification, to give 6 as a 1:4 
(4) For Diels-Alder additions to AS-pyrrolin-2-ones with carbon eub- 
stituenta at  (2-5, see: (a) Vedejs, E.; Campbell, J. B., Jr.; Gadwood, R. 
C.; Rodgere, J. D.; Spear, K. L.; Watanabe, Y .  J. Org. Chem. 1982,47, 
1534. (b) Stork, G.; Nakahara, Y.; Nakahara, Y.; Greenlee, W. J. J. Am. 
Chem. SOC. 1978,100,7775. (c) Ohfune, Y.; Tamita, M. J. Am. Chem. 
SOC. 1982,104,3511. (d) Harkin, S. A; Singh, 0.; Thomas, E. J. J. Chem. 
Soc., Perkin Trans. 1 1984,1489. (e) Ackermann, J.; Matthea, M.; Tamm, 
C. Helu. Chim. Acta 1990, 73, 122. (D Meyers, A. I.; Bueacca, C. A. 
Tetrahedron Lett. 1989,30, 6973. 
(5) For a review, see: Hiemstra, H.; Speckamp, W. N. In Compre- 
hensiue Organic Synthesis; Trost, B. M., Fleming, I., Eda; Pergamon: 
Oxford, 1991; Vol. 2, Chapter 4.5. 
(6) (a) Vedejs, E.; Gadwood, R. C. J. Org. Chem. 1978, 43, 376. (b) 
Baker, J. T.; Sifniades, S. J. Org. Chem. 1979,44,2798. (c) Schmidlin, 
T.; Tamm, C. Hela Chim. Acta 1980,63, 121. 
(7) (a) Chamberlin, A. R.; Chung, Y. L. J. Am. Chem. SOC. 1983,105, 
3653. (b) Hart, D. J.; Yang, T.-K. J. Org. Chem. 1985,50, 235. 
0 1992 American Chemical Society 


Synthesis of allylazo compounds by reactions of aryldiazonium salts with allylsilanes

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Open Access LMU ( Ludwig-Maximilians-Univ. München)

J. Org. Chem. 1992,57,1057-1059 1067 The Journal of Organic Chemistry VOLUME 57, NUMBER 4 FEBRUARY 14,1992 0 Copyright 1992 by the American Chemical Society Communications Synthesis of Allylazo Compounds by Reactions of Aryldiazonium Salts with Allylsilanes Herbert Mayr**t and Klaus Grimm Znstitut fur Chemie der Medizinischen Universitdt zu Lubeck, Ratzeburger Allee 160,D-2400 Lubeck, Germany Received September 27, 1991 Summary: Aryldiazonium tetrafluoroborates react with allylsilanes to yield allylazo compounds. If the allylic carbon attached to the azo group carries hydrogen, tau- tomerization with formation of hydrazones takes place. The coupling of aryldiazonium ions with arylamines and phenols, discovered by Griess in 1858; has been one of the most important reactions in industrial chemistry for more than a century.2 Among the aliphatic C-nucleophiles previously reported to react with diazonium ions, CH- acidic compounds,3a enol enamines,3c and 1,3- dienmM are the most important ones. Marxmeier and Pfeil have found that the 2,4-dinitrobenzenediazonium ion la also reacts with ordinary alkenes, often with cleavage of the original CC double bond as shown in Scheme I.4 Though allylsilanes have been combined with a manifold of electrophiles: reactions with diazonium ions have not yet been reported. Since the nucleophilicity of allyltri- methylsilene is similar to that of those alkenes? which are known to be susceptible to electrophilic attack by la, the electrophilicity of la should also be sufficient for a reaction with allylsilanes. Combination of the y,y-disubstituted allylsilanes 2a-2g with 2,4dinitrobenzenediazonium tetrafluoroborate la in acetonitrile givm the a l l y h  compounds 3a-3g in 38-94% yields (Table I).’ This reaction thus provides a straightforward access to allylazo compounds, which are of interest as precursors to allyl radicals! Representatives of this class of compounds have previously been synthes- ized by treatment of sulfamides (from allylamines and N-sulfonylaniline) with NaOCl and NaOHQ or by sigma- tropic rearrangements of diazenes, which have been gen- erated by oxidation of N-allyl-N-arylhydrazine~.~ ‘Present address: Institut f k  Organische Chemie der Technis- chen Hochschule Darmstadt, Petersenstr. 22, W-6100 Darmstadt, Germany. OO22-3263/92/ 1957-1057$03.00/0 Scheme I NO, NO2 la 18 Zh 0 2 N Q N e N a  r.QN,NO/B NO2 NOz 3h 4h The reaction of methallyltrimethylsilane 2h with la BFL initially yields the crystalline allylazo compound 3h, which (1) Griess, P. Liebigs Ann. Chem. 1868, 106, 123. (2) (a) Szele, I.; Zollinger, H. Top. Curr. Chem. 1983, 112, 1. (b) Hegarty, A. F. In The Chemistry of Diazonium and Dbzo Groups; Patai, S. ,  Ed.; Wiley: Chichestsr, 1978; p 611. (c) Schmdehotte, K. H. Meth- oden der Organischen Chemie (Houben- Weyl-Mfiller); Thieme: Stutt- part, 1965; Vol. X/3, p 213. (d) Saunders, K. H.; Allen, R. L. M. Aromatic Diazo Compounds; Edward Arnold London, 1983. (3) (a) Parmerter, S. M. Org. React. 1969,10,1. (b) Terent’ev, A. P.; Jagorsvkii, V. A. Zh. Obshch. Khim. 1966, 26, 211. (c) Crary, J. W.; Quayle, 0. R.; Lester, C. T. J.  Am. Chem. Soc. 1956,78,5584. (d) Huisgen, R.; Bronberger, F. Tetrahedron Lett. 1984, 25, 57. (e) Huisgen, R.; Bronberger, F. Tetrahedron Lett. 1984,25,61. 0 1992 American Chemical Society 1058 J. Org. Chem., Vol. 57, No. 4, 1992 Communications Table I. Allylazo Compounds from y,y-Disubstituted Allylsilanes 2 and 2,4-Dinitrobenzenediaeonium Tetrafluoroborate la  dylailanes 2 products 3 (% yield) NMR chemical shifts" rSiMq rSiMe3 0"""" SiMe, v &SiMe3 84 69 38b 59 41b 59 94 24.46 (q), 74.75 (a), 115.01 (t), 141.32 (d) 19.68 (q), 24.07 (q), 76.85 (a), 112.79 (t), 147.13 (e) 23.92 (t), 35.29 (t), 86.53 (a), 115.21 (t), 139.67 (d) 22.27 (t), 25.60 (t), 33.94 (t), 76.66 (4, 117.06 (t), 140.08 (d) 22.57 (t), 30.34 (t), 35.90 (t), 80.59 (4, 115.19 (t), 141.34 (d) 18.51 (t), 25.72 (q), 29.19 (q), 31.25 (91, 36.76 (4, 37.54 (t), 40.60 (t), 77.17 (d, 111.40 (t), 159.63 ( 8 )  "Aryl-C C-16 149.96-150.43 (E), C-2 6 = 144.51-144.81 (E), C-3 6 120.24-120.51 (d), C-4 6 = 147.01-147.22 (E), C-5 6 128.30-128.42 (d), C-6 6 = 120.39-121.05 (d). bUnidentified hydrazones were also formed. Scheme I11 has been stored in the dark at -20 "C for several months. At room temperature, rearrangement to the hydrazone 4h (4) Marxmeier, H.; Pfeil, E. Chem. Ber. 1964, 97, 53. (5) (a) Weber, W. P. Silicon Reagents for Organic Synthesis; Springer-Verlag: Berlin, 1983. (b) Schinzer, D. Synthesis 1988,263. (c) Fleming, I. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Eds.; Pergamon Press: Oxford, 1979 Vol. 3, p 541. (d) Sakurai, H. Pure Appl. Chem. 1985, 57, 1759. (e) Colvin, E. Silicon in Organic Synthesis; Butterworths: London, 1981. (6) (a) Mayr, H.; Schneider, R.; Irrgang, B.; Schade, C. J .  Am. Chem. SOC. 1990,112,4459. (b) Mayr, H. Angew. Chem. 1990,102,1415; Angew. Chem., h t .  Ed. Engl. 1990,29,1371. (c )  Hagen, G.; Mayr, H. J. Chem. SOC., Chem. Commun. 1989,91. (d) Hagen, G.; Mayr, H. J. Am. Chem. SOC. 1991,113,4954. (7) Typical Procedure. Allylsilane 2b (0.530 g, 2.67 mmol) was added to a suspension of 2,4-dinitrobenzenediazonium tetrafluoroborate (0.500 g, 1.77 mmol) in dry acetonitrile. The mixture was stirred until the diazonium salt dissolved. After addition of water, the mixture was ex- tracted with two 10-mL portions of CH,Cl,. The organic layers were dried over CaCl, and evaporated. After purification of the residue by column chromatography (silica gel, CHzClz/pentane, 70/30) product 3b was ob- tained and recrystallized from pentane: Orange plates (0.340 g, 69%), mp 55-56 'C. Table 11. Relative Reactivities of the Allylsilanes 2a-2h toward (p-HSCOC6H4)PhCH+ and Their Ability To React with Diazonium Ions reaction with kre? la  lb l c  2i 1 + - - 2j 6.60 + - - 2c -7 + + - 2d -7 + + - 2e -7 + + - 2a 7.92 + + - 2h 508 + + - 2f - 103 + + I 2B - 103 + + + 2b 1675 + + + From ref 6 4  estimates marked by the - sign are baaed on k,, values of structurally analogous compounds. is detectable after several hours. This tautomerization is very fast in chloroform solution (not purified from traces of HC1) or during chromatography on silica gel. Analo- gously, the reaction of 2i and 2j with la yields the hy- drazones 4i and 4j as stable final products. Allylsilanes with one or two hydrogen atoms in y-position thus can (8) (a) Luedtke, A.; Meng, K.; Timberlake, J. W. Tetrahedron Lett. 1987,28,4255. (b) Adams, J. S.; Burton, K. A.; Andrew, B. K.; Webman, R. B.; Engel, P. S. J. Am. Chem. SOC. 1986, 108, 7935. (c) Roesi, M.; Golden, D. M. J. Am. Chem. SOC. 1979,101, 1230. (d) Crawford, R. J.; Takagi, K. J. Am. Chem. SOC. 1972, 94, 7406. (e) Crawford, R. J.; Hamelin, J.; Strehlke, B. J. Am. Chem. SOC. 1971,93,3810. (0 AI-Sader, B. H.; Crawford, R. J. Can. J .  Chem. 1970,48,2745. (g) Porter, N. A.; Iloff, P. M. J. Chem. SOC., Chem. Commun. 1971, 1575. (9) Baldwin, J. E.; Brown, J. E.; Hbfle, G. J. Am. Chem. SOC. 1971.93, 788. J.  Org. Chem. 1992,57,1059-1061 1059 oxidatively be desilylated by treatment with aryldiazonium ions. Preliminary experiments showed that among the allyl- silanes used in this work all but 2i and 2j also react with the leas electrophilic pnitrobemnediazonium ion lb. The highly alkylated allylsilanes 2b and 2g even react with the unsubstituted benzenediazonium ion IC to give 3b' and 3g' in 51 and 74% yield, respectively. In accord with our previous report that allylstannanes are more nucleophilic than structurally analogous allylsilanes by several orders of magnitude,Bd tri-n-butylprenylstannane also reacted with the parent benzenediazonium ion IC to afford 49% of 3a'. Though the correlation between reactivities toward car- benium and diazonium ions does not seem to be perfect, Table I1 shows that the nucleophilicity scale developed with respect to diarylcarbenium ionse also allows one to roughly predict the feasibility of electrophilic attack of diazonium ions at  allylsilanes. 4 N  0 N? l b  IC 3a' 3b' ON+?? 3g' ON..* O N + N ) +  Registry No. la, 345-12-0; lb,  456-27-9; IC, 369-57-3; 2a, 18293-99-7; 2b, 64545-12-6; 2c, 834386843; 2d, 63922-76-9; 2e, 138061-12-8; 2f, 138061-13-9; 2g, 138061-14-0; 2h, 18292-38-1; 2i, 762-72-1; 2j, 14579-08-9; 3a, 138061-15-1; 3a', 31928-42-4; 3b, 138061-16-2; 3b', 138061-17-3; 3c, 138061-18-4; 3d, 138061-19-5; 3e, 138061-20-8; 3f, 138061-21-9; 3g, 138061-22-0; 3#, 138061-23-1. (R)-l-Acetyl-5-isopropoxy-3-pyrrolin-2-one: A Versatile Chiral Dienophile from (S)-Malic Acid Wim-Jan Koot, Henk Hiemstra,* and W. Nico Speckamp* Department of Organic Chemistry, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands Received October 28, 1991 Summary: The title compound, readily prepared from @)-malic acid, reacts as a Diels-Alder dienophile with several 1,3-&enes with excellent regio- and stereoselectivity without loss of enantiomeric purity. The synthesis of an enantiomerically pure intermediate in a projected synthesis of gelsemine is detailed. Of the various ways to control the absolute stereochem- istry of an intermolecular Diels-Alder reaction, the ap- proach involving the use of an enantiomerically pure dienophile has proven to be most practicable.' In this paper we wish to present the synthesis and utility of the chiral dienophile (R)-l-acetyl-5-isopropoxy-3-pyrrolin-2-one (l), which in essence can be viewed as an enantiomerically pure synthetic equivalent of maleimide.2 Me H ~w&o - acid Hwq@o Me Me X,.\%.QO E* ,."' *Q0 OAMe M e A M e  A A 1 2 3s R = A C  4 3b R = H  The choice for the structural features present in 1 was eventually made, when we had found that other A3- pyrrolin-2-ones such as Z3 were unsuitable for our purposes. The isopropoxy function at  C-5 in 1 is meant to direct l,&dienes to react at  the opposite face of the molecule to give 3ae4 The significance of an alkoxy function at  C-5 (1) For reviews, see: (a) Paquette, L. A. In Asymmetric Synthesis; Morrison, J. D., Ed.; Academic: New York, 1984; Vol. 3, Chapter 7. (b) Oppolzer, W. Angew. Chem., Int. Ed. Engl. 1984,23,876. (2) For recent alternative approaches, see: (a) Arai, Y.; Matsui, M.; Kolzumi, T.; Shiro, M. J. Org. Chem. 1991,56,1983. (b) Baldwin, S. W.; Greenspan, P.; Alaimo, C.; McPhail, A. T. Tetrahedron Lett. 1991, 32, 5877. For a chiral synthetic equivalent for maleic anhydride, see: (c) Feringa, B. L.; de Jong, J. C. J. Org. Chem. 1988,53,1125. (d) de Jong, J. C.; Janaen, J. F. G. A.; Feringa, B. L. Tetrahedron Lett. 1990,31,3047. (3) The study of 2 originated from our work on the synthesis of the indole alkaloid peduncularine and will be described in a full paper; see: Klaver, W. J.; Hiemetra, H.; Speckamp, W. N. J. Am. Chem. SOC. 1989, I1 1 ,  2588. 0022-326319211957-1059$03.00/0 Scheme I" 5 6 7 1 "Reagenta and conditions: (a) (i) LiBHl (1.0 equiv), THF, -20 - 0 "C, (ii) HzS04 in i-PrOH (pH = 3), 0 "C - reflux, 55%; (b) (C13CCO)z0 (1.1 equiv), D W  (1.1 equiv), EhO, -60 "C - rt, 86%; (c) Ac20/pyridine, DMAP (cat.), 0 O C  - rt, 85%. becomes apparent after removal of the N-acetyl function, as 3b is expected to allow the introduction of a variety of substituents via N-acyliminium intermediate 4.6 The presence of the N-acetyl function in 1 is required to pre- vent racemization and enhance the reactivity and regio- chemical bias of the dienophile? The synthesis of (R)-1 is detailed in Scheme I. (S)-3- Acetoxysuccinimide (5), readily prepared on large scale from (S)-malic acid,' was regioselectively reduced with lithium borohydride in THF at -20 OC. The crude reaction mixture was acidified with sulfuric acid. The solvent THF was then substituted for 2-propanol and the resulting mixture heated at  reflux for 18 h to effect both iso- propanolysis and transesterification, to give 6 as a 1:4 (4) For Diels-Alder additions to AS-pyrrolin-2-ones with carbon eub- stituenta at  (2-5, see: (a) Vedejs, E.; Campbell, J. B., Jr.; Gadwood, R. C.; Rodgere, J. D.; Spear, K. L.; Watanabe, Y .  J. Org. Chem. 1982,47, 1534. (b) Stork, G.; Nakahara, Y.; Nakahara, Y.; Greenlee, W. J. J. Am. Chem. SOC. 1978,100,7775. (c) Ohfune, Y.; Tamita, M. J. Am. Chem. SOC. 1982,104,3511. (d) Harkin, S. A; Singh, 0.; Thomas, E. J. J. Chem. Soc., Perkin Trans. 1 1984,1489. (e) Ackermann, J.; Matthea, M.; Tamm, C. Helu. Chim. Acta 1990, 73, 122. (D Meyers, A. I.; Bueacca, C. A. Tetrahedron Lett. 1989,30, 6973. (5) For a review, see: Hiemstra, H.; Speckamp, W. N. In Compre- hensiue Organic Synthesis; Trost, B. M., Fleming, I., Eda; Pergamon: Oxford, 1991; Vol. 2, Chapter 4.5. (6) (a) Vedejs, E.; Gadwood, R. C. J. Org. Chem. 1978, 43, 376. (b) Baker, J. T.; Sifniades, S. J. Org. Chem. 1979,44,2798. (c) Schmidlin, T.; Tamm, C. Hela Chim. Acta 1980,63, 121. (7) (a) Chamberlin, A. R.; Chung, Y. L. J. Am. Chem. SOC. 1983,105, 3653. (b) Hart, D. J.; Yang, T.-K. J. Org. Chem. 1985,50, 235. 0 1992 American Chemical Society 

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Synthesis of allylazo compounds by reactions of aryldiazonium salts with allylsilanes

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