Synthesis of 1,2-Five-Ring-Annellated Barrelenes via the Intramolecular Diels-Alder Reaction of Acetylenic Derivatives

Article abstract of DOI:10.1002/hlca.19870700708

The intramolecular Diels-Alder reaction conducted with acetylenic acylureas, obtained from carbodiimides, and the acetylenic acid 5 and its derivatives 13 gave the 1,2-annellated barrelene 14 (from 13a) and the benzobarrelenes 8 (from 5) and 15 (from 13b); in the case of 3-butyinoic acid (1), <1,3>-H shifts were observed.The formation of the azabarrelenes 16 (from 13c) as an intermediate is postulated which looses HCN to afford the indolinone 17.The acylureas 6 and 9 underwent isocyanate cleavage instead of <4 + 2> cyclization.