Asymmetric Construction of Quaternary Carbon Centers by Regio- and Enantiocontrolled Allylzincation
摘要:
[GRAPHICS]An allylic zinc reagent bearing a chiral bisoxazoline ligand adds to a substituted cyclopropenone acetal to produce an optically active cyclopropanone acetal possessing a quaternary chiral center in high yield with 97.8-99.8% ee, The steric effects of the bulky bisoxazoline ligand overwhelm the regioselectivity inherent to the electronic property of the olefinic acceptor. High pressure exerts favorable effects on the reaction rate without affecting the high enantio- or regioselectivity.
A variety of substituted cyclopropanone acetals were prepared by the addition of an organozinc reagent or a Grignard reagent to a substituted cyclopropenone acetal. MnO2- or PbO2-mediated oxidative ringopening reaction of the substituted cyclopropanone acetals affords β-alkoxyesters and protected β-aminoesters with high efficiency.
General synthesis of cyclopropenones and their acetals
作者:Masahiko Isaka、Satoshi Ejiri、Eiichi Nakamura
DOI:10.1016/s0040-4020(01)88873-6
日期:——
Metalated cyclopropenone acetals 5 react with a variety of electrophiles, including alkyl halides, carbonylcompounds, vinyl iodides, vinyl triflates, and aryl iodides, to give substituted cyclopropenone acetals in high yield. Hydrolysis of the acetal under acidic conditions gives the corresponding cyclopropenone. The reaction sequence has realized an efficient synthesis of an antibiotic penitricin
Thermal reactions of substituted cyclopropenone acetals. Regio- and stereochemistry of vinylcarbene formation and low-temperature [3 + 2] cycloaddition
of diverse electronic character have been synthesized and examined for their thermal behavior toward water and electron-deficient olefins. The substituted cyclopropenes underwent regio- and stereoselective hydration to give acrylate derivatives via vinylcarbene species, providing new data on the regio- and stereochemistry of vinylcarbene species. The also underwent regioselective [3+2] cycloadditions
A new and simple method for the synthesis of highly functionalised pyrrolizidines, indolizidines and pyrroloazepines
作者:Paul A. O’Gorman、Ting Chen、Hannah E. Cross、Saleena Naeem、Arnaud Pitard、M. Ilyas Qamar、Karl Hemming
DOI:10.1016/j.tetlet.2008.08.061
日期:2008.10
The reaction of 5-, 6- and 7-membered cyclic thioimidates with cyclopropenones gives access to highly functionalised pyrrolizidines, indolizidines and pyrroloazepines via a formal [3+2] cycloaddition process.
[reaction: see text] Substituted cyclopentadienone acetals (CPDAs) were synthesized by a thermal or palladium-catalyzed [3 + 2] cycloadditionreaction of a substituted cyclopropenone acetal to an electron-deficientacetylene. The synthesis afforded di-, tri-, and tetra-substituted CPDAs of considerable structural varieties that undergo Diels-Alder reaction to produce bicyclo[2.2.1]heptenes.