The development of novel small molecules-based catalysts for organic transformations has increased noticeably in the last two decades. A very recent addition to this particular research area is cyclopropene- and...

A Pd-catalyzed direct method has been developed to access 1,3-disubstituted indolizines. This reaction proceeds through a regiospecific annulation of terminal alkynes with 2-pyridinyl-substituted p-quinone methides and, in most of the...

The catalytic application of the bis­(amino)­cyclopropenium ion has been investigated in conjugate addition reactions. The hydrogen atom, which is attached to the cyclopropene ring of bis­(amino)­cyclopropenium salts, is moderately acidic and can potentially serve as a hydrogen-bond donor catalyst in some organic transformations. This hypothesis has been successfully realized in the 1,6-conjugate addition reactions of p-quinone methides with various nucleophiles such as indole, 2-naphthol, thiols, phenols, and so forth. The spectroscopic studies (NMR and UV–vis) as well as the deuterium isotope labeling studies clearly revealed that the hydrogen atom (C–H) that is present in the cyclopropene ring of the catalyst is indeed solely responsible for catalyzing these transformations. In addition, these studies also strongly indicate that the C–H hydrogen of the cyclopropene ring activates the carbonyl group of the p-quinone methide through hydrogen bonding.