Syntheses of 3-substituted 2,3-dihydrobenzofuranes, 1,2-dihydronaphtho(2,1-b)furanes, and 2,3-dihydro-1H-indoles by tandem ring closure-S(RN)1 reactions.

Abstract

3-Substituted 2,3-dihydrobenzofuranes (7a-c), 1,2-dihydronaphtho(2,1-b)furanes (10a-c), and N-substituted 2,3-dihydro-1H-indoles (8a-c, 9a,b) are obtained in very good yields by S(RN)1 photostimulated reactions in liquid ammonia from adequate haloaromatic compounds ortho-substituted with a suitable double bond (3a,b; 4a,b; 5a; 6a,b) and Me3Sn-, Ph2P-, and -CH2NO2 anions. The novelty of the work involves the versatile application of a 5-exo ring closure process during the propagation cycle of the S(RN)1 reaction; the alkyl radical intermediates formed react with the nucleophiles to afford the ring closure-substituted heterocycles. The factors governing the observed product distribution are discussed.