The formation of a thermally unstable (4+2)-cycloadduct, a 4H-1,2-oxazine 2-oxide derivative ( ), from the reaction of 1-nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene has been proven by the structure elucidation of isoxazole derivative  which results from thermal rearrangement and by the structure determination of the 1,3-dipolar adducts  of  with electron-deficient acetylenes

Pennings, M.L.M.

Reinhoudt, D.N.

English

The formation of a thermally unstable (4+2)-cycloadduct, a 4H-1,2-oxazine 2-oxide derivative ( ), from the reaction of 1-nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene has been proven by the structure elucidation of isoxazole derivative which results from thermal rearrangement and by the structure determination of the 1,3-dipolar adducts of with electron-deficient acetylenes

Reinhoudt, David

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(4+2)-cycloaddition of nitroalkenes with ynamines; formation of a 4H-1,2-oxazine 2-oxide derivative

University of Twente Research Information

Tetrahedron Letters Vol. 21, pp 17el - 1784 @Pergamon Press Ltd. 1960. Printed in Great Britain (4+2)-CYCLOADDITION OF NITROALKENES WITH YNAMINES; FORMATION OF A 4H-1,2-OXAZINE 2-OXIDE DERIVATIVE M.L.M. Pennings and D.N. Reinhoudt* (Laboratory of Organic Chemistry, Twente University of Technology, Enschede, The Netherlands) Abstract: The formation of a thermatty unstable (4+2)-cycloadduct, a 4H-1,2-oxazine Z-oxide deriuat57)e (1). from the reaction of I-nitrocucEoventene with I-whenuZ-d- (I-pyrro2idinyZlacetyZenh has been proven by the stru"ctur'e eZucidation o‘f is&ca- zoZe derivative 3 which results from thermal rearPangement"and by the structure determination of-the 1,3-dipalar adducts J of 2 with etectron-deficient anetytenes. Although the formation of 4H-1,2-oxazine 2-oxides has been reported by Stetter and Hoehnel, the proposed structure was after a period of confusion2,3 proven to be incorrect by an X-ray analysis4. The only six-membered cyclic nitronic esters that are known are 5,6-dihydro-4H-1,2-oxazine 2-oxides516. In this paper we describe such a hitherto unknown I&1,2-oxazine 2-oxide derivative from the reaction of l- nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene. Contrary to Nielsen and Archibald5 who have stated that an ynamine failed to react with l-phenyl-2- nitropropene, we have recently found that nitroalkenes undergo a facile reaction with ynamines to yield both 3-nitrocyclobutenes and nitrones716. The formation of the nitrones was accounted for by a two-step process: (4+2)-cycloaddition to yield a 4H-1,2-oxazine 2-oxide and subsequent ring contraction9. 1-Nitrocyclopentene and 1-phenyl-2-(l-pyrrolidinyl)acetylene react in light pe- troleum atroam temperature to yield in addition to a nitrobicyclo[3.2.07hept-6-ene another 1:l reaction product (35%, MS: M+284.15 (C17H20N202). IR(KBr): 1640 cm-' (C=N and C=C). UV: Amax 230 nm)l". Attempts to purify the crude product failed be- cause of its thermal instability. Even in the crystalline state or in chloroform solution atroom temperature it isomerises almost quantitatively to 3-phenyl-3-(l- pyrrolidinylcarbonyl)-3a,4,5,6-tetrahydro-3~-cyclopent~elisoxazole 3 (scheme l), 1761 m.p. 109.5-110.5°C (white crystals from light petroleum). MS: M+ 284.15 (C17Hzo N 2 0 2 1 . IR(KBr): 1640 cm-1 (C=N and C=O). lH NMR G(CDC1,): 2.6-2.9 and 3.2-3.6 (m,4H,CHz-N), 4.91 (dd,J1 llHz,J,8Hz,lH,H-3a), 7.2-7.5 (m,5H,Harom) ppm. 13C NMR data of 2 were compared with those of N,N-diethyl-3,3a-dihydro-3-methylbenzofuro [3,2-clisoxazole-3-carboxamide S, which was obtained from the reaction of 3-nitro- benzocblfuran with 1-diethylaminopropyne (see table): the structure of 3 was elu- cidated by X-ray analysisll. The formation of 2 can be explained, assuming the initial product of the reac- tion between 1-nitrocyclopentene and l-phenyl-2-(l-pyrrolidinyl)acetylene is the 4H-1,2-oxazine 2-oxide derivative 1. Homolytic cleavage of the weak N-O bond in 1 gives the diradical 2. Similar diradicals react further by the formation of a C-N bond to give 2,3-dihydro-azete l-oxides like 6a7. However in the case of the fused - 4H-1,2-oxazine 2-oxide derivative 1, this would lead to the nitrone 6b which has a - bridgehead sp' -hybridized carbon atom in a four-membered ring. Consequently 2 re- acts by formation of a C-O bond to yield the isoxazole derivative 2 (see also ref. 11). Further support for structure 1 has been obtained from the identification of the reaction products of the 1,3-dipolar additionsI of 1 with electron-deficient acetylenes. Reaction of 1 with dimethyl acetylenedicarboxylate or methyl propio- late in chloroform solution at rccm temperature afforded the cycloadducts 5 (scheme 2)13. R-C=C-E 25=‘C/CHCI, 0 8-N C6H5 4 5 E = CCOCH3 a R=E b. R=H Since the bridgehead carbon atom in the intermediates 2 is no longer sp2-hybrid- ized, ring contraction to 2 no longer leads to the formation of an anti-Bredt type of compound like e. The tricyclic products 5a and 5b were obtained as white - solids in 83 and 85% yield respectively; 5a: m.p. 14O-142q (from benzene/hexane). - MS: M+ 426.18 (CZ3HZ6Nz06). IR(XBr): 1755 and 1715 cm -1 (COOCH3), 1640 and 1660 cm -1 (C=C and C=O). lH NMR G(CDC13): 3.1-3.6 (m,4H,CH2-N), 3.76 and 3.88 (s,3H, O-CH3)r 4,66 (dd,J,8Hz,J11Hz,lH,H-3a), 6.7-7.0 (m,lH,o-Harem), 7.1-7.5 (m,3H, H arom )I 7.8-8.1 (m,lH,o-Harom)ppm. z: rnry. 124-126OC (from light petroleum). MS: M+ 368.17 (C21H2~N20t,). IR(KBr): 1730 cm (COOCH,) and 1630 cm-l (C=C and C=O). lH NMR G(CDC13): 3.2-3.6 (m,4H,CHz-N), 3.80 (s,3H,O-CH3), 6.00 (s,lH,H-8), 6.7- , 7.0 (m,lH,o-Harem ), 7.1-7.6 (m,3H,Harom), 7.9-8.2 (m,lH,o-Harom)ppm. The formatio& of 5a and 5b occurs stereospecifically and from the nonequivalence of the ortho- - - phenyl protons in the 'H NMR spectra can be concluded, that the phenyl ring and the cyclopentane ring are on the same side of the azetidine ring. A molecular model shows that in this configuration of 5 the rotation around the CgHg-C-4 bond - is restricted. The structures of 5a and 5b were also confirmed by comparison of - - the 13C NMR data of 5a and 5b with those of dimethyl 1,6a-dihydro-l,Z-diphenyl- - - 6a-methyl-2-(l-pyrrolidinylcarbonyl)-2H-azeto[l,2-~~isoxazole-5,6-dicarboxylate 2 (see table). For this purpose compound 1 has been prepared by 1,3-dipolar addi- tion of dimethyl acetylenedicarboxylate with the cyclic nitrone e7. After 18 hours stirring in chloroform solution at room temperature, z was isolated as a white solid, m.p. 142-144OC. MS: M + 476.19 (C27H28N206)_ IR(XBr) : 1755 and 1715 cm -' (COOCH3), 1650 cm-l (C=O and C=C). *H NMR G(CDC13): 1.25 (s,3H,CH3), 3,58 and 3.79 (s,3H,O-CH3), 5.19 (s,iH,H-11, 7.1-7.9 (m,lOH,Harom) ,ppm. E _6 2 R1=CH,,R2=C6H5 b R,R2 = tCH2j3 7 E q  CCXXH, 8 Table 3 - 94.4 c-3 63.2 C-3a 167.4 C-6a 171.2 c=o 8 5a 5b 7 - - - _ 94.6 c-3 153.3 147.1 c-7 152.9 c-5 96.6 c-3a 110.1 112.4 C-8 115.4 C-6 167.3 C-8b 82.1 81.4 C-8a 16.5 C-6a 169.8 c=o 50.9 51.9 C-3d 51.6 C-l 84.7 85.1 C-4 82.6 c-2 165.5 166.5 ;N-C=O 167.7 >N-C=O 161.8 158.6 -o-c=0 162.1 -o-c=0 159.1 -o-c=0 158.1 -o-c=0 -._~- Characteristic 13 C NMR absorptions of compounds 3,5a,5b,7 and 8 _----~ ~11 chemical shifts were recorded in deuterrochloroform with TMS as internal standard (6 in ppm) Acknowledgement. This investigation was supported by the Netherlands Foundation for Chemical Research (SON) with financial aid from the Netherlands Organization for Advancement of Pure Research (ZWO). 1784 References and notes 1. H. Stetter and K. Hoehne, Chem. Ber., 91, 1344 (1958). 2. A.T. Nielsen and T.G. Archibald, Tetrahedron, 25, 2393 (1969). 3. H.O. Larson, T.-C. Ooi, A.K.Q. Siu, K.H. Hollenbeak and F.L. Cue, Tetrahe- dron, 2, 4005 (1969). 4. G.B. Ansell, D.W. Moore and A.T. Nielsen, J. Chem. Sot. (B), 1971, 2376. 5. A.T. Nielsen and T.G. Archibald, Tetrahedron, 26, 3475 (1970). 6. G. Pitacco and E. Valentin, Tetrahedron Lett., 1978, 2339 7. A.D. de Wit, M.L.M. Pennings, W.P. Trompenaars, D.N. Reinhoudt, S. Harkema and 0. Nevestveit, J. Chem. Sot. Chem. Commun., 1979, 993. 8. D.N. Reinhoudt and C.G. Kouwenhoven, Reel. Trav. Chim. Pays Bas, 95, 67 (1976). 9. In our first paper8 the formation of N-heteroaryl-C-carbamoyl nitrones was attributed to a two-step process involving a (2+2)-cycloaddition of the yna- mine to the N=O bond of the nitro group. 10. Dilute solutions of this product were studied by 'H and 13C NMR spectroscopy, but the presence of radical species made this impossible. In the case of 13C NMR only minor amounts of rearranged product 3 could be traced. 11. See preceeding paper. 12. A.T. Nielsen in 'The Chemistry of the nitro and nitroso groups', ed. H. Feuer, J. Wiley & Sons, New York, 1969; part I, p. 349. 13. The isoxazole derivative 3 failed to react with - dimcthyl acetylenedicarbox- ylate under the same reaction conditions. (Received in UK 4 March 1980) 

(4+2)-cycloaddition of nitroalkenes with ynamines; formation of a 4H-1,2-oxazine 2-oxide derivative

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