1994 Volume 52 Issue 6 Pages 498-509
The synthetic potential of 1-cyclobutenyl ketones (1) has been studied. First the ring expansion reactions of 1 to five-, six-, and eight-membered rings were examined. The reaction of 1 with 1, 3-dienes gave the Diels-Alder adducts (2), which were easily transformed to the hydrindanones by the treatment with ethylaluminum dichloride. The adducts (2) were also found to be good intermediates for the synthesis of 1-acetyl-1, 3, 5-cyclooctatrienes by the electrocyclic reaction. 1-Cyclobutenyl ketones (1) serve as diene components as well as dienophiles in Diels-Alder reaction : 1-acetyl-1-cyclohexenes were fomed when 1 were heated with various dienophiles at elevated temperatures. The alternative way to construct cyclohexenes using 1 as starting materials consists of the conjugate addition of 1-alkenylmagnesium bromides followed by the ethylaluminum dichloride-promoted ring enlargement reaction. Next the ring opening reactions of cyclobutanes derived from 1 were examined. 2- (Trimethylsilylmethyl) cyclobutyl ketones (3), which were prepared by the conjugate addition of trimethylsilylmethylmagnesium chloride to 1, were treated with a catalytic amount of triethylaluminum to give (Z) -6- (trimethylsiloxy) -1, 5-heptadienes stereoselectively.. Furthermore, the stereoselective addition of alkylmetals to 3 and the zinc bromide-catalyzed stereospecific ring opening reaction of the resulting alcohols or their methyl ethers gave (E) - and (Z) -1, 5-dienes with high stereoselectivity.. The highly stereoselective synthesis of various trisubstituted olefins using 2-phenylthiocyclobutyl ketones is also described.
