Synthesis of cyclopropanols
The reaction of bimetallic CH2(ZnI)2 with α-chloroaldehydes enables a diastereoselective synthesis of trans-2-substituted cyclopropanols in very good yields and dr’s. The high trans-selectivity resulted from equilibration of the cyclopropoxide intermediates.
K. Cheng, P. J. Carroll, P. J. Walsh, Org. Lett., 2011, 13, 2346-2349.
1-Substituted cyclopropanols are formed in high yields in the titanium(IV)isopropoxide-catalyzed reaction of esters with ethylmagnesium bromide.
O. G. Kulinkovich, S. V. Sviridov, D. A. Vasilevski, Synthesis, 1991, 234.
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.
A diastereofacial selective attack of epoxy ketones by bis(iodozincio)methane leads to 2-(1-hydroxyalkyl)-1-alkylcyclopropanols in good yields. The dizinc reagent, which acts as an effective bidentate Lewis acid, is easily prepared from diiodomethane and zinc powder.
K. Nomura, K. Oshima, S. Matsubara, Angew. Chem. Int. Ed., 2005, 44, 5860-5863.
A sequence of two gold(I)-catalyzed isomerization steps allows the synthesis of functionalized acetoxy bicyclo[3.1.0]hexenes from 5-en-2-yn-1-yl acetates. Acetoxy bicyclo[3.1.0]hexene products can be further transformed to 2-cycloalkenones by simple methanolysis.
A. Buzas, F. Gagosz, J. Am. Chem. Soc., 2006, 128, 12614-12615.
Regioselective dichlorocyclopropanation of 2-silyloxydienes furnishes vinylcyclopropanol silyl ethers in good yield. Treatment with silver(I) at room temperature effects disrotatory electrocyclic opening to a 2-chloro-3-silyloxypentadienyl cation, which then undergoes a Nazarov reaction to provide chlorocyclopentenones.
T. N. Grant, F. G. West, J. Am. Chem. Soc., 2006, 128, 9348-9349.