Utility of α-halodicyclopentadienones for the synthesis of novel fused heterocycles

Abstract

A base-mediated Michael addition of amidines, oxindoles and thio-oxindoles to α-halodicyclopentadienones (halo-DCPD-enones) followed by cyclization of the intermediate Michael adducts leads to linear fused tetracycles to hexacycles with complete diastereoselectivity. While amidines and thio-oxindoles react with halo-DCPD-enones to deliver fused imidazoles and thienoindoles via 1,3-addition–cyclization, oxindole takes part in a 1,1-addition–cyclization to produce spirocyclopropyl oxindoles in good to excellent yields. The divergent reactivity of oxindoles and thio-oxindoles with α-halodicyclopentadienones was rationalized by DFT calculations. Our method is operationally simple and suitable for the gram-scale synthesis of the title polycycles.