Reactivity of Functionalized N,S-Ketene Acetal: Regioselective Construction of Tetrahydrobenzo[b]pyran and Chromeno[2,3-b]quinoline Derivatives

Regioselective synthesis of functionalized tetrahydrobenzo[b]pyrans has been developed by multi-component reactions (MCRs) and tandem [3 + 3] annulations of beta-benzoylthioacetanilides or beta-(2-haloaroyl)thioacetanilides as valuable sources with aromatic aldehydes and 5,5-dimethy1-1,3-cyclohexanedione catalyzed by triethylamine. This MCR followed by a postcondensation cyclization via an intramolecular SNAr in the presence of K2CO3 led to an unprecedented novel chromeno-[2,3-b]quinoline framework containing an important chromene moiety in good yields. The reactions were very mild, convenient, and o-selective to form new fused tetracyclic target molecules.