Steric buttressing in the Pauson–Khand reactions of aryl enynes
摘要:
A variety of aryl enynes have been constructed from o-iodophenol derivatives containing ortho-tert-butyl groups via O-alkylation and a Sonogashira cross-coupling reaction. These substrates undergo efficient thermal and oxidative intramolecular Pauson-Khand reactions leading to the formation of sterically congested cyclopentenones, as well as the formation of medium-sized rings, although in the latter case with unusual regioselectivity. Incorporation of a TMS moiety on the alkyne group in a higher homolog led to cyclization via the normal mode, albeit in relatively low yield. (c) 2007 Elsevier Ltd. All rights reserved.
Synthesis of Bridged Medium-Sized Rings through the Intramolecular Pauson−Khand Reaction
摘要:
[GRAPHICS]A series of aromatic enynes containing steric buttressing elements were prepared and evaluated in the NMO-mediated Pauson-Khand cyclization. O-Allyl systems led to the expected angularly fused products, whereas the O-butenyl and O-pentenyl derivatives afforded the unprecedented bridge systems.
Steric buttressing in the Pauson-Khand reactions of benzyl enynes
作者:Christian E. Madu、H.V. Rasika Dias、Carl J. Lovely
DOI:10.1016/j.tet.2017.08.053
日期:2017.10
the former case, the diastereoselectivities are high. An investigation of the tolerance of this cycloaddition to substitution around the 1,8-enyne demonstrates that only 2,2-disubstitution does not result in productive cyclization. Cycloadditions with hydroxyl groups at the propargylic position while leading to fused rings are compromised by side reactions leading to reduction and in some cases tautomerization