Catalytic cyclopropanation of electron deficient alkenes mediated by chiral and achiral sulfides: scope and limitations in reactions involving phenyldiazomethane and ethyl diazoacetate
作者:Varinder K. Aggarwal、Helen W. Smith、George Hynd、Ray V. H. Jones、Robin Fieldhouse、Sharon E. Spey
DOI:10.1039/b004367m
日期:——
Phenyldiazomethane reacts with electron deficient alkenes in the presence of catalytic amounts of transition metal catalyst [Rh2(OAc)4 was better than Cu(acac)2] and catalytic amounts of sulfide to give cyclopropanes. Pentamethylene sulfide was found to be superior to tetrahydrothiophene and the optimum solvent was toluene. Under these optimised conditions a range of enones were cyclopropanated in
A general method for the preparation of α-phenylselanyl enones is described. Phosphorus ylides react with these α-phenylselanyl enones in a 1,4-addition, leading to cyclopropanes and/or dihydrofurans, depending on the substitution pattern. This unusual reactivity is due to the phenylselanyl moiety, hindering the carbonyl of the enone and making it less prone to 1,2-additions or promoting conjugate
Catalytic asymmetric cyclopropanation of electron deficient alkenes mediated by chiral sulfides
作者:Varinder K. Aggarwal、Helen W. Smith、Ray V. H. Jones、Robin Fieldhouse
DOI:10.1039/a704214k
日期:——
Catalytic asymmetric cylopropanation of enones has been achieved using
diazo compounds, catalytic quantities of a metal catalyst and a
camphor-derived thioacetal; this sulfide shows exceptionally high levels
of enantioselectivity.
aziridines and cyclopropanes (see scheme, PTC=phase-transfer catalyst, Ts=toluene-4-sulfonyl) in good yield with moderate to high d.r. and high ee values using tosylhydrazone salts with catalytic quantities of chiral sulfide (5-20 mol %) and metal catalyst (1 mol %). The process is particularly suited to the synthesis of conformationally locked cyclopropyl amino acids, which can now be prepared in only