The Silylalkyne-Prins Cyclization: Stereoselective Synthesis of Tetra- and Pentasubstituted Halodihydropyrans
作者:Pedro O. Miranda、Miguel A. Ramírez、Víctor S. Martín、Juan I. Padrón
DOI:10.1021/ol060247m
日期:2006.4.1
[reaction: see text] A new type of Prins cyclization using silylated secondary homopropargylic alcohols and aldehydes yielding tetra- and pentasubstituted dihydropyrans is described. The presence of the trimethylsilyl group in the triple bond favors the Prins cyclization and minimizes the 2-oxonia-[3,3]-sigmatropic rearrangement as a competitive alternative pathway. Ab initio theoretical calculations
A Ru-Catalyzed Tandem Alkyne−Enone Coupling/Michael Addition: Synthesis of 4-Methylene-2,6-<i>cis</i>-tetrahydropyrans
作者:Barry M. Trost、Hanbiao Yang、Georg Wuitschik
DOI:10.1021/ol0520065
日期:2005.10.1
[reaction: see text] A Ru-catalyzed tandem alkyne-enone coupling/Michael addition reaction is reported. It provides an efficient, atom-economic entry to 4-methylene-2,6-cis-tetrahydropyrans from simple, readily available homopropargylic alcohols and beta,gamma-unsaturated enones in good yields. Further functionalization of the resultant vinylsilane leads to the synthesis of either geometrically defined
Various cerium allenyl reagents were generated by trans- metallation of allenyl Grignard compounds with CeCl3 and sub- sequent conversion into homopropargylic alcohols by addition to various aliphatic and aromatic aldehydes. The a-acetylenic alcohols were obtained with regioselectivities and diastereoselectivities up to 98% de in favor of the threo-diastereomers.