Ring-Enlarging Annulatons. A One-Step Conversion of Cyclic Silyl Acyloins and ω-Alkynyl Acetals to Polycyclic Enediones

Article abstract of DOI:10.1021/jo00107a011

A new sequence of cationic reactions that converts cyclic silyl acyloins and ω-alkynyl acetals to polycyclic enediones is reported.For example, treatment of bis-1,2-((trimethylsilyl)oxy)cyclobutene and 2-(ethylenedioxy)-5-heptyne with excess boron trifluoride etherate in methylene chloride for 2 days provides 4-acetyl-3,5,6,6a-tetrahydro-6a-methyl-1-(2H)-pentalenone in 58percent yield.This product is formed via a sequence involving a Mukaiyama aldol reaction, a pinacol ring expansion, and a 5-exo-dig alkynyl ketone cyclization.In the case of terminal alkynes, the last cyclization occurs in a 6-endo-dig fashion.The scope and limitations of this process are studied, and a number of bi- and tricyclic ring systems are formed.