Tetra- and pentaalkylated cyclopentadienyl ketones and carboxylic acids are prepared by electrophilic allylation of enolizible 1,3-dicarbonyl compounds and successive acid catalyzed cyclisation

Koschinsky, Rainer

Köhli, Thies-Peter

Mayr, Herbert

English

Universität München: Elektronischen Publikationen

Tetrahedron Letters,Vol.29,No.44,pp 5641-5644,1988 0040-4039/88 $3.00 + .OO 
Printed in Great Britain Peraamon Press plc 
SYNTHBIS OF HIalLY iulKYIAm FuNcrIoNALIzED CYCLoPEWrADIENgs 
Rainer Koschinsky, Thies-Peter KGhli, and Herbert Mayr* 
Institut fiir Chemie der Medizinischen Universitgt zu Liibeck 
Ratzeburger Allee 160, D-2400 Liibeck 1, Federal Republic of Germany 
Abstract. Tet ra- and pentaalkylated cyclopentadienyl ketones and carboxylic acids are 
prepared by electrophilic allylation of enolizible 1,3-dicarbonyl compounds and successive 
acid catalyzed cyclisation. 
The pentamethylcyclopentadienyl group is an important ligand in organometallic chemistry, 
end various synthetic approaches to pentamethylcyclopentadiene and its derivatives have 
been developed.’ We report now a novel and straightforward access to highly alkylated 
acetyl- and alkoxycarbonylcyclopentadienes, which employs the [3+ + 21 strategy, previously 
developed for the synthesis of cyclopentenes by Lewis acid catalyzed reaction of ally1 
chlorides with alkenes’ or alkynes.’ 
JY / la 
Cl 
lb 
ou / lc
Cl 
0 
* 
\ / II 
R2 P 
+ R 
0 
II & \ 
3a (60%) 
3b (70x1 
R’.R’=CH C H 3. 2 5 
or C,H,,CH, 
3C (60%1 
When the allylic chlorides la-c (25 mm01 in 50 ml of CH,Cl,) were added dropwise to a 
solution of acetylacetone 2a (33 tmaol) end ZnCl,/Et,O* (52 mmol) in CH,Cl, (350 ml) at 
-2OOC and kept at -20% for 1 d and at 4% for 2 d, the cyclopentadienes 3a-c were isolated 
in 60-70% yield after workup with aqueous ammonia and chromatographic removal5 of small 
5641 
5642 
amounts of the dihydrofurans 9a-c. As expected, traces of isomers (< 5%) with different 
orientation of the endocyclic double bonds were detectable in the NMR spectra of 3a,b. 
The reactions are suggested to proceed via the allylated dicarbonyl compounds 6a-c, - 
(Scheme) which are isolated aa the only products when the reactions are carrried out at 
-78°C.6 Treatment of 6a-cwith ZnCl,/Et,O/HCl inCH,Cl, at -20°C yields the cyclopentadienes 
3a-c (60-70%) accompanied by small amounts of the dihydrofurans 9a-c (3-20%). These 
heterocycles are isolated as the major products, when 6a-c are treated with dry HCl in 
CH,Cl, at O°C. As shown in the Scheme, the formation of the dihydrofurans 9a-c is ra- 
tionalized by protonation of the CC-double bond of 6 to give the carbenium ion 7 which 
attacks at the lone pair of the carbonyl group. 
Scheme 
R* R2 R2 
4a-c R’ fast R’LL R&_/- + + -l-i* .. 
5 a-c 6a-c 7a-c 
3a-c 8a-c 9a-c lOa-c 
4-10: a: R’= R*=CH, ; b: R1.R2=CH3,C2H5; c: R’-R2= -(CH2)&- 
When the trimethylallyl chloride la was reacted with the dicarbonyl compounds 2b-d under 
the conditions described above, a complex mixture of compounds was produced, prdbably 
because of self-condensation reactions of la. The corresponding cyclopentadienes 3d-P are 
generated, however, when the acyclic products 6d-f, which are formed from la and 2b-d in 
presence of ZnCl,/Et.O/Et,N, are treated with one equivalent of FSO,H in CH,Cl,. 
5643 
J&H, 
2b 
3d t&8%1 
I$ -k la 
FSOSH !? 
ZnCIz/Et,O/ -78 to -2OT 
NEt3 6e 
-3 
\ 
2c 
I80%1 
3e (53%) 
We are presently exploring the scope of this reaction. Until now, we have not yet succeeded 
to obtain cyclopentadienes from ally1 chlorides, which are unsubstituted in the central 
allylic position’ or which carry two alkyl groups at the same allylic terminus. 
Table. "C NMR Chemical. Shifts of the Cyclopentadienes 3a-f" 
3a-d 3e-f 
R R’ X C-l c-2 c-3 c-4 c-5 1-c 2-c 3-c 4-c 5-c X,&R' 
3a H H CHH. 142.6 154.9 135.7 150.1 49.7 194.3 14.5 10.7 12.4 14.9 30.4 
3b, CH, H G-l. 143.0 154.4 141.9 149.9 49.7 194.2 14.3 18.3 12.1 15.0 30.4, 14.1' 
3b, H a,'% 142.8 154.7 135.1 156.1 47.4 194.3 14.5 10.6 19.8 14.8 30.4, 14.3' 
% G-,-m c-l, 142.8 154.0 138.6 153.4 48.5 194.4 13.9 22.41 22.6* 14.8 30.4, 22.7*, 23.9' 
34H HOCH, 131.8 156.7 135.2 149.3 49.6 165.5 13.8 10.6 12.3 14.7 50.5 
3e H H CH. 137.0 139.4 139.4 137.0 71.4 10.2 11.4 11.4 10.2 14.5, 207.9, 22.7 
31 H H OC,H, 136.5 137.6 137.6 136.5 63.6 10.3 11.3 11.3 10.3 18.4, 174.0. 60.3, 14.3 
5644 
Acknowledgement. We thank Ms. Diana Schnoor for experimental assistance and the Deutsche 
Forschungsgemeinschaft and the Fonds der Chemischen Industrie for financial support. 
References and Notes 
I) (a) L. de Vries, J. Org. Chem. 25, 1838 (1960). (b) L. A. Paquette, G. R. Krow, 
Tetrahedron Lett. 1968, 2139. (c) R. Criegee, H. Griiner, Angew. Chem. 80, 447 (1968); 
Angew. Chem. Int. Ed. Engl. 7, 467 (1968). (d) M. Kunz, W. Liittke, Chem. Ber. 103, 315 
(1970). (e) R. B. King, A. Efraty, J. Am. Chem. Sot. 9’1, 3773 (1972). (f) R. B. King 
W. D. Douglas, A. Efraty, Organic Synth. Coll. Vol. VI, Wiley, New York 1988, p. 39. 
(g) U. Burger, A. Delay, F. Mazenod, Helv. Chim. Acta 57, 2106 (1974). (h) D. Feitler, 
G. M. Whitesides, Inorg. Chem. 15, 466 (1976). (i) R. F. Childs, M. Zeya, J. Am. Chem. 
sot. 96, 6418 (1974). (j) R. S. Threlkel, J. E. Bercaw, J. Organomet. Chem. 136, 1 
(1977). (k) F. X. Kohl, P. Jutzi, J. Organomet. Chem. 243, 119 (1983). (1) U. 
Burger, R. Etienne, Helv. Chim. Acta 67, 2057 (1984). (m) H. A. Brune, P. Lath, G. 
Schmidtberg, Chem. Ber. 118, 2671, 2681 (1985). (n) H. Otto, H. Werner, Chem. Ber. 12% 
97 (1987). (0) F.X. Kohl, P. Jutzi, Chem. Ber. 120, 1539 (1987). 
2) H. Klein, H. Mayr, Angew. Chem. 93, 1069 (1981); Angew. Chem. Int. Ed. Engl. 20, 
1027 (1981). 
3) (a) J. A. Miller, M. Moore, Tetrahedron Lett. 21, 577 (1980). (b) B. D. Gray, C.M. 
McMillan, J. A. Miller, M. Moore, Tetrahedron Lett. 28, 235 (1987). (c) B. D. Gray, 
C. M. McMillan, J. A. Miller, G. M. Ullah, Tetrahedron Lett. 28, 689 (1987). 
4) H. Mayr, W. Striepe, J. Org. Chem. 50, 2995 (1985). 
5) In order to prevent decomposition of the products, NH,-saturated mixtures of hexane/ 
ether have to be used for the chromatographic separations on silica. 
6) Examples of other acid catalyzed alkylations of B-dicarbonyl compounds: 
(a) H. 0. House “Modern Synthetic Reactions” 2nd ed., Benjamin, Menlo Park, 1972, p. 
533. (b) M. T. Reetz, Angew. Chem. 94, 97 (1982); Angew. Chem. Int. Ed. Engl. 21, 96 
(1982). 
7) Cf: H. Mayr. H. Klein, G. Kolberg, Chem. Ber. 117, 2555 (1984). 
8) The IR and 'H NMA spectra of the previously prepared compounds 3e,f agree with 
literature reports.' 
(Received in Germany 19 August 1988) 


Synthesis of highly alkylated functionalized cyclopentadienes

Open Access LMU

Tetrahedron Letters,Vol.29,No.44,pp 5641-5644,1988 0040-4039/88 $3.00 + .OO Printed in Great Britain Peraamon Press plc SYNTHBIS OF HIalLY iulKYIAm FuNcrIoNALIzED CYCLoPEWrADIENgs Rainer Koschinsky, Thies-Peter KGhli, and Herbert Mayr* Institut fiir Chemie der Medizinischen Universitgt zu Liibeck Ratzeburger Allee 160, D-2400 Liibeck 1, Federal Republic of Germany Abstract. Tet ra- and pentaalkylated cyclopentadienyl ketones and carboxylic acids are prepared by electrophilic allylation of enolizible 1,3-dicarbonyl compounds and successive acid catalyzed cyclisation. The pentamethylcyclopentadienyl group is an important ligand in organometallic chemistry, end various synthetic approaches to pentamethylcyclopentadiene and its derivatives have been developed.’ We report now a novel and straightforward access to highly alkylated acetyl- and alkoxycarbonylcyclopentadienes, which employs the [3+ + 21 strategy, previously developed for the synthesis of cyclopentenes by Lewis acid catalyzed reaction of ally1 chlorides with alkenes’ or alkynes.’ JY / la Cl lb ou / lc Cl 0 * \ / II R2 P + R 0 II & \ 3a (60%) 3b (70x1 R’.R’=CH C H 3. 2 5 or C,H,,CH, 3C (60%1 When the allylic chlorides la-c (25 mm01 in 50 ml of CH,Cl,) were added dropwise to a solution of acetylacetone 2a (33 tmaol) end ZnCl,/Et,O* (52 mmol) in CH,Cl, (350 ml) at -2OOC and kept at -20% for 1 d and at 4% for 2 d, the cyclopentadienes 3a-c were isolated in 60-70% yield after workup with aqueous ammonia and chromatographic removal5 of small 5641 5642 amounts of the dihydrofurans 9a-c. As expected, traces of isomers (< 5%) with different orientation of the endocyclic double bonds were detectable in the NMR spectra of 3a,b. The reactions are suggested to proceed via the allylated dicarbonyl compounds 6a-c, - (Scheme) which are isolated aa the only products when the reactions are carrried out at -78°C.6 Treatment of 6a-cwith ZnCl,/Et,O/HCl inCH,Cl, at -20°C yields the cyclopentadienes 3a-c (60-70%) accompanied by small amounts of the dihydrofurans 9a-c (3-20%). These heterocycles are isolated as the major products, when 6a-c are treated with dry HCl in CH,Cl, at O°C. As shown in the Scheme, the formation of the dihydrofurans 9a-c is ra- tionalized by protonation of the CC-double bond of 6 to give the carbenium ion 7 which attacks at the lone pair of the carbonyl group. Scheme R* R2 R2 4a-c R’ fast R’LL R&_/- + + -l-i* . 5 a-c 6a-c 7a-c 3a-c 8a-c 9a-c lOa-c 4-10: a: R’= R*=CH, ; b: R1.R2=CH3,C2H5; c: R’-R2= -(CH2)&- When the trimethylallyl chloride la was reacted with the dicarbonyl compounds 2b-d under the conditions described above, a complex mixture of compounds was produced, prdbably because of self-condensation reactions of la. The corresponding cyclopentadienes 3d-P are generated, however, when the acyclic products 6d-f, which are formed from la and 2b-d in presence of ZnCl,/Et.O/Et,N, are treated with one equivalent of FSO,H in CH,Cl,. 5643 J&H, 2b 3d t&8%1 I$ -k la FSOSH !? ZnCIz/Et,O/ -78 to -2OT NEt3 6e -3 \ 2c I80%1 3e (53%) We are presently exploring the scope of this reaction. Until now, we have not yet succeeded to obtain cyclopentadienes from ally1 chlorides, which are unsubstituted in the central allylic position’ or which carry two alkyl groups at the same allylic terminus. Table. "C NMR Chemical. Shifts of the Cyclopentadienes 3a-f" 3a-d 3e-f R R’ X C-l c-2 c-3 c-4 c-5 1-c 2-c 3-c 4-c 5-c X,&R' 3a H H CHH. 142.6 154.9 135.7 150.1 49.7 194.3 14.5 10.7 12.4 14.9 30.4 3b, CH, H G-l. 143.0 154.4 141.9 149.9 49.7 194.2 14.3 18.3 12.1 15.0 30.4, 14.1' 3b, H a,'% 142.8 154.7 135.1 156.1 47.4 194.3 14.5 10.6 19.8 14.8 30.4, 14.3' % G-,-m c-l, 142.8 154.0 138.6 153.4 48.5 194.4 13.9 22.41 22.6* 14.8 30.4, 22.7*, 23.9' 34H HOCH, 131.8 156.7 135.2 149.3 49.6 165.5 13.8 10.6 12.3 14.7 50.5 3e H H CH. 137.0 139.4 139.4 137.0 71.4 10.2 11.4 11.4 10.2 14.5, 207.9, 22.7 31 H H OC,H, 136.5 137.6 137.6 136.5 63.6 10.3 11.3 11.3 10.3 18.4, 174.0. 60.3, 14.3 5644 Acknowledgement. We thank Ms. Diana Schnoor for experimental assistance and the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for financial support. References and Notes I) (a) L. de Vries, J. Org. Chem. 25, 1838 (1960). (b) L. A. Paquette, G. R. Krow, Tetrahedron Lett. 1968, 2139. (c) R. Criegee, H. Griiner, Angew. Chem. 80, 447 (1968); Angew. Chem. Int. Ed. Engl. 7, 467 (1968). (d) M. Kunz, W. Liittke, Chem. Ber. 103, 315 (1970). (e) R. B. King, A. Efraty, J. Am. Chem. Sot. 9’1, 3773 (1972). (f) R. B. King W. D. Douglas, A. Efraty, Organic Synth. Coll. Vol. VI, Wiley, New York 1988, p. 39. (g) U. Burger, A. Delay, F. Mazenod, Helv. Chim. Acta 57, 2106 (1974). (h) D. Feitler, G. M. Whitesides, Inorg. Chem. 15, 466 (1976). (i) R. F. Childs, M. Zeya, J. Am. Chem. sot. 96, 6418 (1974). (j) R. S. Threlkel, J. E. Bercaw, J. Organomet. Chem. 136, 1 (1977). (k) F. X. Kohl, P. Jutzi, J. Organomet. Chem. 243, 119 (1983). (1) U. Burger, R. Etienne, Helv. Chim. Acta 67, 2057 (1984). (m) H. A. Brune, P. Lath, G. Schmidtberg, Chem. Ber. 118, 2671, 2681 (1985). (n) H. Otto, H. Werner, Chem. Ber. 12% 97 (1987). (0) F.X. Kohl, P. Jutzi, Chem. Ber. 120, 1539 (1987). 2) H. Klein, H. Mayr, Angew. Chem. 93, 1069 (1981); Angew. Chem. Int. Ed. Engl. 20, 1027 (1981). 3) (a) J. A. Miller, M. Moore, Tetrahedron Lett. 21, 577 (1980). (b) B. D. Gray, C.M. McMillan, J. A. Miller, M. Moore, Tetrahedron Lett. 28, 235 (1987). (c) B. D. Gray, C. M. McMillan, J. A. Miller, G. M. Ullah, Tetrahedron Lett. 28, 689 (1987). 4) H. Mayr, W. Striepe, J. Org. Chem. 50, 2995 (1985). 5) In order to prevent decomposition of the products, NH,-saturated mixtures of hexane/ ether have to be used for the chromatographic separations on silica. 6) Examples of other acid catalyzed alkylations of B-dicarbonyl compounds: (a) H. 0. House “Modern Synthetic Reactions” 2nd ed., Benjamin, Menlo Park, 1972, p. 533. (b) M. T. Reetz, Angew. Chem. 94, 97 (1982); Angew. Chem. Int. Ed. Engl. 21, 96 (1982). 7) Cf: H. Mayr. H. Klein, G. Kolberg, Chem. Ber. 117, 2555 (1984). 8) The IR and 'H NMA spectra of the previously prepared compounds 3e,f agree with literature reports.' (Received in Germany 19 August 1988) 

5) In order to prevent decomposition of the products, NH,-saturated mixtures of hexane/ ether have to be used for the chromatographic separations on silica. 6) Examples of other acid catalyzed alkylations of B-dicarbonyl compounds:

8) The IR and 'H NMA spectra of the previously prepared compounds 3e,f agree with literature reports.'

House “Modern Synthetic Reactions”

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Synthesis of highly alkylated functionalized cyclopentadienes

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