Direct and efficient N-heterocyclic carbene-catalyzed hydroxymethylation of aldehydes
作者:Nadine Kuhl、Frank Glorius
DOI:10.1039/c0cc02416c
日期:——
The N-heterocyclic carbene-catalyzed coupling of several aldehydes with paraformaldehyde is reported, directly providing the corresponding valuable hydroxymethyl ketones. Results of first mechanistic experiments for this remarkably selective transformation are also provided.
Enantioselective 1,3-Dipolar (5+3) Cycloadditions of Oxidopyrylium Ylides and Vinylcyclopropanes toward 9-Oxabicyclononanes
作者:Yanfeng Gao、Yuanhao Mao、Zhiwei Miao
DOI:10.1021/acs.orglett.2c01037
日期:2022.4.29
We have developed an efficient and mild enantioselective palladium-catalyzed (5+3) cycloaddition of vinylcyclopropanes and oxidopyryliumylides generated in situ from benzopyranones, in the presence of a chiral PHOX ligand. These reactions afford various highly functionalized bridged oxa-[3.3.1]carbocycles with three stereogenic centers that are challenging to synthesize, in moderate to good yields
Silver-Catalyzed Tandem Cycloisomerization/[5 + 2] Cycloaddition of 3-Cyclopropylideneprop-2-en-1-ones with Oxidopyrylium Ylides to Form Bibridged Benzocycloheptanones
cycloisomerization/[5 + 2] cycloaddition reactions between readily accessible cyclopropyl-tethered allenyl ketones and benzopyranone-derived oxidopyrylium ylides. The reactions proceed via a cyclobutene-fused furan intermediate generated in situ by a cycloisomerization/1,2-carbene transfer/ring-expansion cascade. This method, which features an unprecedented formal [5 + 2] cycloaddition, delivers good to