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24.4.2.1.4.5 Variation 5: From Acetates

DOI: 10.1055/sos-SD-024-00925

Witulski, B.; Alayrac, C.Science of Synthesis, (200624942.

This method was designed for the synthesis of 13C-labeled alk-1-ynyl ethers but it can also be useful for the preparation of derivatives bearing labile groups such as a 6-chlorohexyloxy substituent.[‌57‌] Thus, the syntheses of alkoxyacetylenes 40 are achieved in two steps starting from an acetate 38. Enolization of the starting material by the action of lithium diisopropylamide and subsequent treatment of the enolate with phosphoryl chloride gives an enol phosphate 39, that is transformed via phosphate elimination into the alkoxyacetylene 40 (Scheme 11). Unfortunately, this transformation cannot be performed in a one-pot fashion, because side reactions, such as 1,2-phosphate migration or elimination of the alkoxy group, occur. However, enol phosphates 39 are selectively converted into the ethers 40 by performing the elimination reactions with tert-butyllithium at 100°C, in lithium chloride free pentane, followed by direct treatment of the intermediates with propan-2-ol at low temperature.

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