Isothiourea-Mediated Asymmetric Functionalization of 3-Alkenoic Acids
摘要:
Isothiourea HBTM-2.1 promotes the catalytic asymmetric alpha-functionalization of 3-alkenoic acids through formal [2 + 2] cycloadditions with N-tosyl aldimines and formal [4 + 2] cycloadditions with either 4-aryltrifluoromethyl enones or N-aryl-N-aroyl diazenes, providing useful synthetic building blocks in good yield and with excellent enantiocontrol (up to >99% ee). Stereodefined products are amenable to further synthetic elaboration through manipulation of the olefinic functionality.
Exploiting the Imidazolium Effect in Base-free Ammonium Enolate Generation: Synthetic and Mechanistic Studies
作者:Claire M. Young、Daniel G. Stark、Thomas H. West、James E. Taylor、Andrew D. Smith
DOI:10.1002/anie.201608046
日期:2016.11.7
function as ammonium enolate precursors in the absence of base. Enantioselective Michael addition–cyclization reactions using different α,β‐unsaturated Michael acceptors have been performed to form dihydropyranones and dihydropyridinones with high stereoselectivity. Detailed mechanistic studies using RPKA have revealed the importance of the “imidazolium” effect in ammonium enolateformation and have highlighted