Formation of anti‐Bredt‐type azabicyclo[4.2.0]octene frameworks through photochemical intramolecular [2+2] cycloaddition between indole and a distal double bond of allene

Abstract

Irradiation of 1‐(penta‐3,4‐dienoyl)indole derivatives in the presence of an aromatic ketone by a high‐pressure mercury lamp through Pyrex glass gave two types of cyclized products stereoselectively in high combined yields. The major product was a tetracyclic indoline derivative containing anti‐Bredt‐type azabicyclo[4.2.0]octene moiety produced via photo [2+2] cycloaddition between indole and a distal double bond of allene, accompanied by a small amount of proximal [2+2] adduct. Among a range of aromatic ketones screened, 3′,4′‐methylenedioxyacetophenone was found to sensitize the substrate most effectively.

Thermally-induced intramolecular [2 + 2] cycloaddition of allene-methylenecyclopropanes: expedient access to two separable spiropolycyclic heterocycles

“…Cyclobutane, as a special strained structure, exists in many natural products and pharmaceutical molecules. 1 In general, [2 + 2] cycloaddition is an extremely effective method for the construction of cyclobutane structural motifs 2,3 and it is regarded as a key step in the synthesis of many natural products and so on. 4 In addition, [2 + 2] cycloaddition reactions, which do not produce any waste, have attracted great attention from chemists in recent years as an ideal process in terms of atom economy.…”