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32.2 Product Class 2: Monofunctionalized Allenes and Higher Cumulenes

DOI: 10.1055/sos-SD-032-00025

Hashmi, A. S. K.Science of Synthesis, (20083223.

General Introduction

Allenes 1 with only one heteroatom on the cumulated diene core represent a large family of compounds which have found widespread use in synthesis. The related butatrienes are much less abundant and due to the synthetic routes to such systems, the unsymmetrical representatives of type 2 are an even smaller subgroup of the small butatriene family (Scheme 1).

Scheme 1 Heteroatom-Substituted Allenes and Butatrienes

While 1 and 2 possess no intrinsic stereochemical properties, with two different substituents at the other end of the cumulated system, allene 1 becomes chiral and two diastereomers of butatriene 2 exist, but examples for a stereoselective synthesis of such substrates are rare. In a number of reports, the allenes of type 1 cannot be isolated, they are only intermediates in reaction cascades, for example the Kanematsu furan ring-transfer reaction, where an alkoxy allene is formed by base-catalyzed isomerization of a propargyl ether and then immediately undergoes cycloaddition with a furan moiety.[‌1‌‌3‌]