Methyleneketenes and methylenecarbenes. IV. Pyrolysis of 5-Heteroarylmethylene-2,2-dimethyl-l,3-dioxan-4,6-diones to give phenolic benzothiophens, benzofurans and indoles

Abstract

The synthetic sequence leading from o-tolualdehyde to 2-naphthol¹ has been applied to seven five membered heterocyclic aldehydes bearing adjacent methyl substituents. Flash vacuum pyrolysis of the corresponding 5-heteroarylmethylene-2,2-dimethyl-1,3-dioxan-4,6-diones gave hydroxy derivatives of the benzologous systems benzothiophene, benzofuran, dibenzofuran, indole and carbazole in 54-98% yield.