Search

While the “normal” cycloaddition between dienes and alkynes leads to formation of six-membered Diels—Alder or hetero-Diels—Alder ring products, the reductive cycloaddition using BEt3 as the active reducing agent and MeOH as the proton donor allows the synthesis of either cyclopentenols (from enals and alkynes) or cyclopentenones (from enoates and alkynes).

Cyclizations of allenyl aldehydes and intermolecular couplings of allenes and aldehydes provide a direct procedure for the preparation of homoallylic alcohols. The couplings and cyclizations involve the use of diorganozinc reagents as reducing agents and Ni(COD) 2 as the catalyst.

The direct cyclization of allenyl aldehydes with organozincs in the presence of Ni(COD)(2) provides synthetically versatile homoallylic alcohols. Both monosubstituted and 1,3-disubstituted allenes participate in the process, with the latter allowing preparation of stereochemically defined trisubstituted alkenes. [reaction: see text]