
Journal of Organic Chemistry p. 299 - 308 (1989)
Update date:2022-08-05
Topics: NMR spectroscopy Catalyst Ketone Stereoselective Diazo compound Intramolecular Reaction Conditions Chemical Reaction Cyclopropane Experimental Intramolecular cyclopropanation
Padwa, Albert
Wisnieff, Thomas J.
Walsh, Edward J.
α-Diazo ketones derived from furanyl- and benzofuranylpropionic acids were prepared, and their rhodium(II) acetate catalyzed behavior was studied.The results are consistent with a mechanism in which the key step involves addition of a keto carbenoid intermediate on to the furanyl ?-bond followed by an electrocyclic ring-opening reaction.In the case of the benzo-substituted furanyl system, the suspected bicyclic intermediate was isolated in high yield and its chemistry was subsequently investigated.The bicyclic ketone derived from 1-diazo-4-(2-benzofuryl)-2-butanone undergoes a novel thermal rearrangement to a benzopyranone derivative.This unexpected transformation can be rationalized in terms of a <4 + 2>-cycloreversion reaction to give an ortho-quinoidal intermediate, which undergoes a subsequent electrocyclic ring closure followed by a 1,3-hydrogen shift.Furans with side chains of various lengths containing a diazomethyl keto group were also studied.The cyclization chemistry of the closely related diazothienylalkanone system was investigated and found to give products derived from an analogous intramolecular cyclopropanation reaction.
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