Science of Synthesis

Kubik, S., Science of Synthesis, (2010) 41, 529.

The base-catalyzed decomposition of N-nitrosocarbamates is a general procedure for the preparation of diazo and diazonium species (see Section ‌41.7.1.1.3.2‌). Cyclic analogues of N-nitrosocarbamates, the N-nitrosooxazolidin-2-ones ‌47‌, exhibit the interesting feature that the alcohol portion of the carbamate remains part of the molecule containing the diazonium group after the ring is opened with a nucleophilic base such as an alkoxide. The subsequent mode of reaction is determined to a large extent by the ease with which the thus-generated intermediate ‌48‌ loses an alkyl carbonate to afford an alkenediazonium compound (e.g., ‌49‌ or ‌54‌) relative to the ease with which it loses nitrogen to produce an sp2-hybridized carbenium ion (e.g., ‌52‌).[‌147‌] As a consequence, the reaction course depends sensitively on the substitution pattern of the starting material. ‌Scheme 37‌ shows that if R1 = H, i.e. if 5,5-disubstituted N-nitrosooxazolidin-2-ones are used, the alkenediazonium intermediate gives mainly an unsaturated carbene ‌50‌[‌129‌] whose reaction with a nucleophile affords the final product, for example ‌51‌.[‌12‌] Depending on the type of nucleophile, basic cleavage of N-nitrosooxazolidin-2-ones has been shown to give access to vinyl halides,[‌148‌] vinyl ethers,[‌149‌,‌150‌] vinylsilanes,[‌148‌,‌151‌] aldehydes,[‌148‌,‌149‌,‌152‌] alkylidenecyclopropanes,[‌149‌,‌151‌,‌153‌] and other vinyl derivatives.[‌12‌,‌154‌–‌156‌] Because of the large migration tendency of aryl rings, 2,2-diaryl-substituted alkenediazonium compounds give diarylacetylenes without intermediate formation of a carbene.[‌152‌,‌157‌]

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References