Annulative ring expansions. Direct conversion of .omega.-alkynyl acetals to polycyclic unsaturated ketones
摘要:
Geminal acylation of omega-acetylenic acetals and bis(silyloxy)cycloalkenes under Lewis acid conditions preceded cationic cyclization of the alkyne onto the ketone to produce polycyclic unsaturated ketones.
Annulative ring expansions. Direct conversion of .omega.-alkynyl acetals to polycyclic unsaturated ketones
作者:Joseph Sisko、Aaron Balog、Dennis P. Curran
DOI:10.1021/jo00042a007
日期:1992.7
Geminal acylation of omega-acetylenic acetals and bis(silyloxy)cycloalkenes under Lewis acid conditions preceded cationic cyclization of the alkyne onto the ketone to produce polycyclic unsaturated ketones.
Ring-Enlarging Annulations. A One-Step Conversion of Cyclic Silyl Acyloins and .omega.-Alkynyl Acetals to Polycyclic Enediones
作者:Aaron Balog、Dennis P. Curran
DOI:10.1021/jo00107a011
日期:1995.1
new sequence of cationic reactions that converts cyclic silyl acyloins and omega-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 58% 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.