4- Alkoxy-3-pyrrolin-2-ones

Reductive formation of pyrroles from pyrrolenones is also feasible. For example reduction of 4-alkoxy-3-pyrrolin-2-ones provides a route to <84JOC3222>. 

The regioselectivity of the 1,3-dipolar cycloadditions of azides to alkenes is usually difficult to predict due to the similar energies for the transition states which involve either the HOMO (dipole) or the LUMO (dipole). The results of a study which utilized 5-alkoxy-3-pyrrolin-2-ones as dipolar-ophiles in reactions with a variety of aryl azides seemed to reflect this problem the results suggested that the low regioselectivity observed was due to the frontier molecular orbital interactions between dipole and dipolarophile, and not any steric hindrance offered by the 5-alkoxy function <84H(22)2363>. 

In a similar fashion, 5-alkoxy-butyrolactones can undergo addition and elimination to give substituted 3-pyrrolin-2-ones. In 1973, Farina and coworkers found that 5-methoxyfuran-2-one 575 treated with aqueous ammonia gives 5-hydroxy-3-pyrrolin-2-one 576 (Scheme 165 1973S167). Ten years later. Farina and coworkers showed that primary amines, such as benzylamine, give 5-hydroxy-3-pyrrolin-2-ones when stirred with 2-chloro-5-methoxyfuran-2-one (1983H(20)1761). The transformation... 

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