Synthesis of cyclobutanones
Hydroboration of 1-alkynyl-1-boronate esters and in situ transmetalation furnishes 1-alkenyl-1,1-borozinc heterobimetallic intermediates. Reaction with aldehydes and in situ cyclopropanation generates B(pin) substituted cyclopropyl carbinols with excellent diastereoselectivities. Oxidation provides trisubstituted α-hydroxycyclopropyl carbinols, that allow access to both cis- and trans-2,3-disubstituted cyclobutanones via a facile pinacol-type rearrangement.
M. M. Hussain, H. Li, N. Hussain, M. Ureņa, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc., 2009, 131, 6516-6524.
Oxidative ring expansion of methylenecyclopropanes with CAN under oxygen atmosphere was investigated. A facile conversion affording 2,2-diarylcyclobutanones occurred in good yields.
V. Nair, T. D. Suja, K. Mohanan, Synthesis, 2006, 2531-2534.
A stereospecific gold(I)-catalyzed rearrangement of 1-alkynyl cyclobutanols and cyclopropanols provides alkylidene cycloalkanones. The reaction tolerates terminal alkynes as well as alkyl, aryl, and halo-substitution at the acetylenic position and substituents on the ring.
J. P. Markham, S. T. Staben, F. D. Toste, J. Am. Chem. Soc., 2005, 127, 9708-9709.
Halocycloalkenones are potent dienophiles in Diels-Alder cycloadditions. 2-Brominated cycloalkenone dienophiles are highly endo selective and significantly more reactive than their nonhalogenated parent compounds. A base-mediated reaction enables the facile conversion of brominated cyclobutanone Diels-Alder adducts to synthetically useful cyclopropyl derivatives.
A. G. Ross, S. D. Townsend, S. J. Danishefsky, J. Org. Chem., 2013, 78, 204-210.