Science of Synthesis

Griesbeck, A. G.; Soldevilla, A., Science of Synthesis, (2008) 43, 382.

The Seyferth–Gilbert 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 Wittig–Horner-type alkenation to give a diazo intermediate that eliminates dinitrogen with formal formation of a vinylidene carbene. The Bestmann–Ohira 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 Seyferth–Gilbert reagent is more conveniently available from dimethyl methyphosphonate by diazo group transfer.[‌155‌]

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References

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• 8.Meeeee-Meee, (8888) M 88e8, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 8888.