Dynamics of Diels–Alder reactions involving 2-trialkylsilyloxyfurans
摘要:
Increasing the size of the silyl group on 2-trial kylsilyloxyfurans reduces the rate of Diels-Alder reactions with maleic acid derivatives. While the exo-adduct resulted from the reaction between 2-silyloxyfurans and maleic anhydride, endo-adducts resulted from the reactions with maleate esters. Analysis of transition state structures for the cycloaddition, calculated at the B3LYP/6-31G* level of theory, revealed significant stretch-mode asynchronicity in the forming bonds, with selectivity arising from steric interactions that affect torsional strain about the shorter of the forming bonds. (C) 2011 Elsevier Ltd. All rights reserved.
1,4-Addition of silicon dienoates to α,β-unsaturated aldehydes catalyzed by in situ-generated silicon Lewis acid
作者:Hikaru Yanai、Arata Takahashi、Takeo Taguchi
DOI:10.1039/c0cc02438d
日期:——
In situ-generated silyl methide species (R(3)Si-CTf(2)R') effectively catalyzed the reaction of beta-substituted alpha,beta-unsaturated aldehydes with silicon dienoates such as 3-bromo-2-TESO-furan to give the corresponding gamma-adducts with excellent 1,4-selectivity and good anti selectivity.
Highly Effective Vinylogous Mukaiyama−Michael Reaction Catalyzed by Silyl Methide Species Generated from 1,1,3,3-Tetrakis(trifluoromethanesulfonyl)propane
Silyl methide species in situ generated from 1,1,3,3-tetrakis(trifluoromethanesulfonyl)propane (Tf2CHCH2CHTf2) performed as an excellent acid catalyst for the vinylogous Mukaiyama-Michael reaction of alpha,beta-unsaturated ketones with 2-silyloxyfurans. Notably, the required loading of Tf2CHCH2CHTf2 to obtain the 1,4-adducts in reasonable yield was significantly low (from 0.05 to 1.0 mol %). This carbon acid-mediated VMM reaction provides a powerful synthetic methodology to construct highly substituted gamma-butenolide structure.
Catalytic Asymmetric Cascade Vinylogous Mukaiyama 1,6-Michael/Michael Addition of 2-Silyloxyfurans with Azoalkenes: Direct Approach to Fused Butyrolactones
作者:Jun Li、Rong Huang、Yi-Kang Xing、Guofu Qiu、Hai-Yan Tao、Chun-Jiang Wang
DOI:10.1021/jacs.5b06509
日期:2015.8.19
An unprecedented cascade vinylogous Mukaiyama 1,6-MA/MA of 2-silyloxyfurans and azoalkenes was realized with a Cu(II)/Bu-t-Box complex. An array of fused butyrolactones containing multiple stereocenters was generally obtained in good yield (up to 90% yield) with exclusive diastereoselectivity (>20:1 dr) and excellent enantioselectivity (up to 99% ee). Carbon isotope effects measured by C-13 NMR revealed a stepwise mechanism for this annulation process.