Pyranyl lactols

The reactivity of alkynylstannanes toward electrophiles is one element in the oxygen-to-carbon rearrangement of alkynylstannane derivatives of furanyl and pyranyl lactols (e.g., Equation (85)). The cleavage of the anomeric C-O bond is assisted by the Lewis acid to give an oxonium ion, which is trapped in situ by the nucleophilic stannylalkyne. The utility of this process has been demonstrated in the synthesis of the natural product muricatetrocin C, and the drug substance CMI-977.246... 

This reagent has been shown to be particularly effective for the net O to C rearrangement of alkynyl tributylstannane derivatives from mixed acetals derived from furanyl and pyranyl lactols (eq 61). Attempts to accomplish the same transformation with other Lewis acids (TiCLj, SnCLj, EtAlCl2, Me2AlCl) were not successful. 

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