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43.6.1.4.5.3 Variation 3: Seyferth–Gilbert Modification

DOI: 10.1055/sos-SD-043-00304

Griesbeck, A. G.; Soldevilla, A.Science of Synthesis, (200843382.

The SeyferthGilbert reagent, dimethyl diazomethylphosphonate (90), is a valuable reagent for the efficient one-carbon homologation of aldehydes and ketones 89 to alkynes 91 (Scheme 47). The mechanism of its reaction with carbonyl compounds involves WittigHorner-type alkenation to give a diazo intermediate that eliminates dinitrogen with formal formation of a vinylidene carbene. The BestmannOhira reagent, diethyl (1-diazo-2-oxopropyl)phosphonate, reacts by a similar mechanism, but is easier to handle (see Section 43.6.1.4.5.4). In the presence of groups with high migratory ability, alkynes are formed by 1,2-shift. Potassium tert-butoxide is most commonly used to deprotonate the reagent.[‌153‌,‌154‌] The SeyferthGilbert reagent is more conveniently available from dimethyl methyphosphonate by diazo group transfer.[‌155‌]

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