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DOI: 10.1055/sos-SD-021-00115

Judd, W. R.; Katz, C. E.; Aubé, J.Science of Synthesis, (200521145.

Rearrangement of cyclic α-diazo ketones affords ring-contraction products. The photochemical method of effecting rearrangement is especially useful for this purpose, as thermal or metal catalysis often promotes competing reaction pathways, probably as a result of the higher ring strain in the product. Diazo transfer from sulfonyl azides to enolates is the standard method for the preparation of cyclic α-diazo ketones.[‌18‌] Tosyl azide in the presence of a weak base (usually triethylamine) is most frequently used for the conversion of β-diketones into the corresponding 2-diazo-1,3-diketones (CAUTION: many azide transfer reagents are explosive and should be used with caution). Diazo transfer to cyclic mono­ketones is usually best accomplished by prior activation by the formation of α-formyl derivatives (the Regitz procedure)[‌33‌] or trifluoroacetyl derivatives (the Danheiser procedure).[‌34‌]

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