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43.6.1.4.5.4 Variation 4: Bestmann–Ohira Modification

DOI: 10.1055/sos-SD-043-00304

Griesbeck, A. G.; Soldevilla, A.Science of Synthesis, (200843383.

The introduction of the BestmannOhira reagent,[‌156‌‌158‌] dimethyl (1-diazo-2-oxopropyl)phosphonate (93) (see also Section 43.8.2.1.4), in a modification of the SeyferthGilbert process, allows the synthesis of terminal alkynes 95 directly from aromatic aldehydes at room temperature under mild conditions using mild bases (Scheme 48).[‌159‌] Synthesis of the reagent is most convenient on a multigram scale by diazo group transfer from 4-acetamidobenzenesulfonyl azide (preferred to tosyl azide) to dimethyl 2-oxopropylphosphonate (92) (Scheme 48).[‌160‌] Aldehydes can be generated from Weinreb amides or from esters by reduction with diisobutylaluminum hydride and directly used for further reaction with the BestmannOhira reagent.[‌161‌] Alternatively, benzylic alcohols 94 are converted by oxidation with activated manganese dioxide into the corresponding aldehydes and subsequently treated with the alkynylation reagent.[‌162‌]

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