Furo[2,3-g]thieno[2,3-e]indole: Application of an Ynamide-Based Benzannulation Strategy to the Synthesis of a Tetracyclic Heteroaromatic Compound

Abstract

The first synthesis of the tetracyclic aromatic compound furo[2,3-g]thieno[2,3-e]indole ("FTI") is described. The synthetic strategy features a photochemical benzannulation based on the reaction of an α-diazo ketone and ynamide which assembles a benzothiophene equipped with substituents that enable subsequent cyclizations to generate the nitrogen and oxygen heterocyclic rings.

Ring forming transformations of ynamides via cycloaddition

“…Further, the colorless FTI 108 was afforded by passing through several steps such as oxidative cleavage via modied Lemieux-Johnson conditions, deprotection of silyl ethers, and one-pot double cyclization (Scheme 51). 122 2.12.1.2. Total synthesis of anticancer agents (+)-FR66979 and (+)-FR900482.…”

“…Vinyl ketene intermediate reacted with highly substituted benzene in a regioselective [2 + 2]-cycloaddition, 4π-electron electrocyclic ring-opening, and 6π-electrocyclization manner to afford vinylcyclobutenone intermediate, dienylketene intermediate, and tetracyclic aromatic benzannulation product respectively. 122 The synthetic transformation involves the benzannulation of ynamide 1v and diazo ketone 105 via regioselective [2 + 2]-cycloaddition, 4π-electron electrocyclic ring-opening, and 6π-electrocyclization reaction sequence in two steps. The reaction was carried out by irradiation of the degassed solution in dichloromethane at room temperature followed by reflux in toluene as solvent.…”