High Regio-, Chemo-, and Stereoselectivity via Low-Temperature 4 + 3 Cycloadditions. Convergent Synthesis of Multifunctionalized Vinylmetals (M = Si, Sn) and S-Vinyl Benzenecarbothioates
摘要:
[GRAPHICS]A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.
High Regio-, Chemo-, and Stereoselectivity via Low-Temperature 4 + 3 Cycloadditions. Convergent Synthesis of Multifunctionalized Vinylmetals (M = Si, Sn) and <i>S</i>-Vinyl Benzenecarbothioates
作者:Hartmut Beck、Christian B. W. Stark、H. Martin R. Hoffmann
DOI:10.1021/ol991386p
日期:2000.4.1
[GRAPHICS]A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.
Synthesis of polysubstituted 3-thiofurans by regiospecific mono-ipso-substitution and ortho-metallation from 3,4-dibromofuran
作者:Carlos Alvarez-Ibarra、Maria L. Quiroga、Emilio Toledano
DOI:10.1016/s0040-4020(96)00069-5
日期:1996.3
4-disubstituted furans via mono-S-ipso-substitution. The ability of 3-methylthio and 3-phenylthio substituents for directing the metallation at position α-relative to the substituent has allowed the regiospecific alkylation. It provides a straightforward approach to several 3-monothiosubstituted furans which are receiving increasing interest as odour and flavour chemicals.