Bis(amino)cyclopropenium Ion as a Hydrogen-Bond Donor Catalyst for 1,6-Conjugate Addition Reactions.

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 -quinone methides with various nucleophiles such as indole, 2-naphthol, thiols, phenols, and so forth.