Catalytic Cyclooligomerization of Enones with Three Methylene Equivalents
摘要:
Cyclic structures are highly represented in organic molecules, motivating a wealth of catalytic methods targeting their synthesis. Among the various ring-forming processes, cyclooligomerization reactions possess several attractive features but require addressing a unique challenge associated with controlling ring-size selectivity. Here we describe the catalytic reductive cocyclooligomerization of an enone and three carbene equivalents to generate a cyclopentane, a process that constitutes a formal [2 + 1 + 1 + 1]-cycloaddition. The reaction is promoted by a (quinox)Ni catalyst and uses CH2Cl2/Zn as the C-1 component. Mechanistic studies are consistent with a metallacycle-based pathway, featuring sequential migratory insertions of multiple carbene equivalents to yield cycloalkanes larger than cyclopropanes.
Phase-Transfer-Catalyzed Asymmetric Synthesis of Chiral<i>N</i>-Substituted Pyrazoles by Aza-Michael Reaction
作者:Su-Jeong Lee、Ju-Yeon Bae、Chang-Woo Cho
DOI:10.1002/ejoc.201500940
日期:2015.9
cinchona-based phase-transfer-catalyzed asymmetric aza-Michael reaction of pyrazole with various α,β-unsaturated ketones has been developed for the preparation of chiral N-substituted pyrazoles. This reaction provided the desired products in good yields (up to 99 %) with excellent enantioselectivities (87–94 % ee). In addition, the reaction of 3-methyl-1H-pyrazole, an unsymmetrically substituted pyrazole
The reaction of terminal acetylenes with Bu3SnMgMe, Bu3SnA1Et2, or (Bu3Sn)2Zn in the presence of various transition-metal catalysts provides vinylstannanes in good yields. Whereas copper catalysed stannylmagnesation of 4-benzyloxy-1-butyne gives (E)-4-benzyloxy-1-tributylstannyl-1-butene exclusively, palladium catalysed stannylzincation affords 4-benzyloxy-2-tributylstannyl-1-butene preferentially