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Please login to access the full content or check if you have access via Variation 1: (Triphenylphosphoranylidene)ketene and (Triphenylphosphoranylidene)thioketene by Elimination with Sodium Hexamethyldisilazanide

DOI: 10.1055/sos-SD-027-00847

Schobert, R.; Gordon, G. J.Science of Synthesis, (2004271046.

When a solution of (methoxycarbonylmethylene)triphenylphosphorane[‌300‌] in benzene or toluene is mixed with an equimolar quantity of a strong base such as sodium hexamethyldisilazanide or crystalline sodium amide, deprotonation occurs at the ylidic α-carbon atom. After the immediate loss of methoxide ion (β-elimination), the cumulated ylide 146 (X=O) is released (Scheme 52).[‌186‌] If the cheaper sodium amide is used as the base, drastic reaction conditions (refluxing in benzene for several days) are required;[‌565‌] moreover, in this case the initial crude product must be purified by repeated crystallization. Addition of catalytic quantities of hexamethyldisilazane to the suspension of sodium amide in benzene or toluene distinctly improves the reaction time (24h at 60°C) and the product purity.[‌320‌] The pure ylide 146 (X=O) (see Section is obtained in good yield after separation of the byproduct, sodium methoxide. Analogously, (triphenylphosphoranylidene)thioketene 146 (X=S) is prepared from [(methyldithiocarbonyl)methylene]triphenylphosphorane and sodium hexamethyldisilazanide (Scheme 52).[‌186‌,‌565‌]

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