Highly Selective Preparation of Allenic and Homopropargylic Hydrazides through Regiospecific Addition of Propargyltrichlorosilane and Allenyltrichlorosilane to Various Types of N-Acylhydrazones

The highly selective preparation of various types of allenic and homopropargylic hydrazides through regiospecific allenylation and propargylation of the corresponding N-acylhydrazones is reported. These carbon-carbon bond-forming reactions employing in situ prepared propargyl- and allenyltrichlorosilanes proceed smoothly in N,N-dimethylformamide (DMF) without any metal catalysis (neutral Lewis base activation of nucleophiles). The use of Hünig's base as an additive is beneficial in terms of chemical yields.