Chiral alkoxy-allenes synthesis

The first investigations in the 1960s [11,12] established the base-induced isomerization of alkyne precursors as the most practical and general route for the synthesis of alkoxy-and aryloxyallenes. In the meantime, a number of monosubstituted allenes 8 bearing an achiral or a chiral group R is smoothly accessible by this efficient procedure (Scheme 8.5) [1, 2,13-19]. Beside the most commonly used base potassium tert-butoxide, other bases, e.g. n-butyllithium, are also applicable for this isomerization. Recently, the yields of alkyne-allene isomerizations could be significantly increased, in particular with aryloxy-substituted allenes, by using microwave irradiation (Eq. 8.1) [20]. 

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