An asymmetric intramolecular Cannizzaro reaction of aryl and alkyl glyoxals with alcohols has been realized with an unprecedented high level of enantioselectivity, on the basis of a newly developed congested TOX ligand and a gradual liberation protocol of active glyoxals from glyoxal monohydrates. Preliminary results suggested a mechanism of enantioselective addition of alcohols to glyoxals contributing
[3+2]-annulation reaction in the presence of a base. Compounds 6 were easily converted to 2-substituted cyclopent-2-en-1-ones by deethoxycarbonylation. An application of the annulation to synthesis of cis-jasmone is also described.
An environmentally benign catalyst, the N,N′-dioxide–FeCl3 complex, has been developed for the asymmetric intramolecular Cannizzaro reaction with high yields and enantioselectivities.
Brønsted acid activation of α-diazo imide: a syn-selective glycolate Mannich reaction
作者:Timothy L. Troyer、Hubert Muchalski、Jeffrey N. Johnston
DOI:10.1039/b913785h
日期:——
A novel α-diazo imide reagent and its activation by strong Brønsted acid is shown to produce the product of a syn-glycolate Mannich transform with high diastereoselection.
3-Ethoxycarbonyl-2-oxo-propylidenetriphenylphosphorane undergoes a [3+2]-annulation reaction with a variety of glyoxals to give 4-hydroxycyclopentenones in good to moderate yields.