Five-membered heterocycles side-chain reactivity

Sheremetev and co-workers employed diazo compounds of type 60, prepared from the corresponding amines in moderate yields as alternative excellent precursors for the preparation of side-chain-functionalized derivatives (Scheme 29). Several furazans bearing reactive groups or cyclopropyl or five-membered heterocyclic substituents have been prepared by standard procedures (99MI6). 

P-Values for Side-Chain Reactivities of Five-Membered Heterocycles... 

The potential for interaction of the heteroatom (electron donation) with positive charge on a side-chain, especially at an a-position, has a number of effects amongst the most important is the enhanced reactivity of side-chain derivatives carrying leaving groups. Similarly, carbonyl groups attached to five-membered heterocycles have somewhat reduced reactivity, as implied by the resonance contributor shown. 

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