Advances in Metal-Organic Chemistry

Abstract

A new synthesis of pyrrolidine and piperidine derivatives via a chromacyclobutane formed from a Fischer carbene complex and a n enyne having nitrogen in a tether was developed. As the results of the substituent effects, the reaction of enynes having the electron-donating group on the alkene with a Fischer chromium carbene complex in CH3CN afforded preferentially metathesis products, and that of the enyne having the electron-withdrawing group gave the cyclized product fused with a cyclopropane ring. The reactions of dienes, diynes, and enynes with transition metal complexes are very interesting and useful in synthetic organic chemistry. Recent studies of the reaction of enynes with Fischer carbene complexes 2,l which are easily prepared from M(CO)6 (1, M = Cr, Mo, and W) and alkyllithium followed by treatment with alkylating agent, have demonstrated a potential ring construction of bicyclic carbon skeletons (Scheme 1). It was known that the chromium carbene complex did not react with unactivated alkene.2a However, Wulff reported that treatment of enyne 3a with (methoxyeth-y1idene)chromium (4) in CH3CN gave cyclobutanone 5 in 45% yield. When the reaction was carried out in CH3-CN-MeOH, ester 7 was obtained in good yield. He described that the chromium carbene complex did not react with unactivated alkene and cyclobutanone was produced via the [Z + 21 cycloaddition of an alkene of 3a and vinylketene 6 generated by the reaction of alkyne of 3a with chromium carbene complex 4233 (Scheme 2). On the other hand, Hoye reported that the reaction of enyne 3b having an unactivated olefin with chromium carbene complex 4 afforded the cyclopropane derivative 8 in 69% yielde4 It was very interesting that the reaction of enyne 3c with 4 afforded metathesis product 9 although the yield was m ~ d e r a t e. ~ The reaction of activated olefin 3d with the Fischer carbene complex was reported by H a r ~ e y , ~ and he obtained cyclopropane derivative 8d in good yield when molybdenum carbene complex 10a was used. Katz reported that the reaction of enyne 3e with tungsten carbene complex 12 afforded @ Scheme 2 5 3a 6 MeOOC 7 metathesis product 9e in 50% yield6a,b (Schemes 3 and 4). These products were considered to be obtained from complex I11 or W, namely, the reaction of the alkyne moiety of enyne I with the Fischer carbene complex affords vinylcarbene complex 11. If vinylcarbene complex I1 converts into vinylketene complex 111, the [2 + 21 cycloaddition occurs intramolecularly, and if vinyl-carbene complex I1 reacts with the alkene part of the enyne intramolecularly, metallacyclobutane IV is formed. Now, we report the synthesis of heterocycles using the reaction of an enyne having nitrogen in a tether with a Fischer carbene complex. As a result, it was clear that the reaction course was controlled by the electronic factors of the substituent on the alkene' (Scheme 5). Results and Discussion Reaction of an Enyne with Pentacarbonyl-(eth0xyethylidene)chromium. Fischer chromium (6) (a) Katz, T. J.; Sivavec, T. M. J. Am. Chem. Soc. 1985,107, 737. (b) Sivavec, T. M.; Katz, T. J.; Chiang, M. Y.; Yang, G. Xu-Q.