-
Chemistry of dioxenium cations. Synthetic and mechanistic studies on the stereocontrolled formation of tetrahydropyrans from homoallylic alcohols and ortho esters
作者:Francoise Perron-Sierra、Michele A. Promo、Van A. Martin、Kim F. Albizati
DOI:10.1021/jo00021a043
日期:1991.10
Despite their long history, dioxenium cations are underutilized reactive synthetic intermediates. It was found that ortho esters and homoallylic alcohols in the presence of Lewis acids provide 4-heterosubstituted pyranosides in a stereoselective manner. The mechanistic course of events was supported by control experiments and synthesis of a putative mixed ortho ester intermediate which exhibited identical reactivity. A transition state for termination of the dioxenium cation-olefin cyclization is proposed, involving intramolecular delivery of chloride by a coordinated tin species. Structure-reactivity relationships indicate that a cation-stabilizing substituent (alkyl or alkoxy) at the internal position of the olefin is required for cyclization. A variety of 3-alkyl-substituted homoallylic alcohols cyclize cleanly to substituted 2-alkoxytetrahydropyrans in good yield. beta-silyloxy silyl enol ethers were found to smoothly provide 4-oxotetrahydropyranosides when subjected to the same reaction conditions. For these substrates, the course of the cyclization proceeds in a different manner involving a rapid intermolecular Mukaiyama aldol condensation followed by transacetalization.
-
Chemistry of aldolate dianions. β-Silyloxy silyl enol ethers as bifunctional nucleophilic equivalents for oxygen heterocycle synthesis
作者:Van A. Martin、Françoise Perron、Kim F. Albizati
DOI:10.1016/s0040-4039(00)94538-6
日期:1990.1
-
MARTIN, VAN A.;PERRON, FRANCOISE;ALBIZATI, KIM F., TETRAHEDRON LETT., 31,(1990) N, C. 301-304
作者:MARTIN, VAN A.、PERRON, FRANCOISE、ALBIZATI, KIM F.
DOI:——
日期:——
-
MARTIN, VAN A.;MURRAY, DESMOND H.;PRATT, NORMAN E.;ZHAO, YUN-BO;ALBIZATI,+, J. AMER. CHEM. SOC., 112,(1990) N9, C. 6965-6978
作者:MARTIN, VAN A.、MURRAY, DESMOND H.、PRATT, NORMAN E.、ZHAO, YUN-BO、ALBIZATI,+
DOI:——
日期:——
-
Van Martin; Murray, Desmond H.; Pratt, Norman E., Journal of the American Chemical Society, 1990, vol. 112, # 19, p. 6965 - 6978
作者:Van Martin、Murray, Desmond H.、Pratt, Norman E.、Zhao, Yun-Bo、Albizati, Kim F.
DOI:——
日期:——