Science of Synthesis

Mérour, J.-Y.; Joseph, B., Science of Synthesis Knowledge Updates, (2017) 1, 257.

General Introduction

All four isomeric systems, often referred to as “azaoxindoles”, 1,3-dihydro-2H-pyrrolo[3,2-b]pyridin-2-one (‌1‌, 4-azaoxindole),[‌1‌,‌2‌] 1,3-dihydro-2H-pyrrolo[3,2-c]pyridin-2-one (‌2‌, 5-azaoxindole),[‌3‌,‌4‌] 1,3-dihydro-2H-pyrrolo[2,3-c]pyridin-2-one (‌3‌, 6-azaoxindole),[‌1‌,‌5‌,‌6‌] and 1,3-dihydro-2H-pyrrolo[2,3-b]pyridin-2-one (‌4‌, 7-azaoxindole) have been described (‌Scheme 1‌).[‌3‌] The stable form is the carbonyl tautomer; the hydroxy tautomer is predominant where alternative factors favor it, for example with an ester group at C3, which allows stabilization via an intramolecular hydrogen bond. For the most part, there is nothing remarkable about the reactions of azaoxindoles in that they behave as typical five-membered lactams, except that deprotonation α to the carbonyl group, i.e. at C3, occurs more readily than with simple amides. Thus, all isomers will react at C3 in the presence of base with electrophiles such as alkyl halides and aldehydes, the last generally with spontaneous dehydration to form 3-alkylidene-1,3-dihydro-2H-pyrrolopyridin-2-ones.

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References