BF<sub>3</sub>-Catalyzed Reaction of Cyclobutene-1,2-dione Monoacetal and Its Vinylog with Allylsilanes. Regioselective Synthesis of 4-Allyl-4-ethoxycyclobutenones from Squaric Acid and Their Conversion to Bi- and Tricycloalkanones
作者:Yoshihiko Yamamoto、Masatomi Ohno、Shoji Eguchi
DOI:10.1246/cl.1995.525
日期:1995.7
Regioselective allylation of 2,4- and 4,4-diethoxycyclobutenones was performed with allylsilanes in the presence of BF3•Et2O via a common ethoxycarbenium ion intermediate. A merit of this reaction was demonstrated in an efficient conversion of the obtained 4-allyl-4-ethoxycyclobutenones to bi- and tricycloalkanones.
adjacent to an unsaturated four-membered ring are all possible to initiate ring-expansion reactions to five-membered rings including 2(5H)-furanones and cyclopentene-1,3-diones. In these cases, fruitful results were obtained by virtue of effective interaction of the reactive intermediates with the cyclobutenone ring and relief of strain existing in this ring (Scheme 1). Y*: Reactive Intermediate (radical
Formation of 2-[1-(Trimethylsilyl)alkylidene]-4-cyclopentene-1,3-dione from Lewis Acid-Catalyzed Reaction of Cyclobutenedione Monoacetal with Alkynylsilane: Novel Cationic 1,2-Silyl Migrative Ring Opening and Subsequent 5-<i>Exo</i>-<i>Trig</i> Ring Closure
An ethoxycarbenium ion intermediate, which was produced by the catalytic action of a Lewis acid on a cyclobutenedione monoacetal, reacted with phenyl(trimethylsilyl)acetylene to give a normal electrophilic substitution product. In sharp contrast, the same catalytic reaction with bis(trimethylsilyl)acetylene afforded a 2-methylene-4-cyclopentene-1,3-dione derivative as a ring expansion product instead of an alkynylation product. Butyl(trimethylsilyl)acetylene showed reactivity between the aforementioned compounds as a result of the formation of both types of products. In the reactions of such alkyl-substituted silylacetylenes, both E- and Z-isomers of 2-(1-silylalkylidene)cyclopentenediones were obtained in ratios dependent on the reaction temperature and the amount of Lewis acid. This rearrangement resulted from unprecedented cationic 1,2-silyl migration on the alkynylsilane and subsequent ring expansion promoted by the formed vinyl cation intermediate. A detailed mechanism of the novel ring-expansion route is discussed with the aid of PM3 calculations, especially for the reclosure step, which is explained by a 5-exo-trig cyclization rather than a pentadienyl cation electrocyclization.
BELLUS D.; MARTIN P.; SAUTER H.; WINKIER T., HELV. CHIM. ACTA, 1980, 63, NO 5, 1130-1140
作者:BELLUS D.、 MARTIN P.、 SAUTER H.、 WINKIER T.
DOI:——
日期:——
BELLUS D., J. AMER. CHEM. SOC., 1978, 100, NO 25, 8026-8028