Diastereofacial Selectivity in the Cycloaddition of Nitrones to (E)-γ-Oxygenated α,β-Unsaturated Esters
摘要:
The 1,3-dipolar cycloadditions of nitrones 1 and 2 to a series of 1,2-disubstituted electron-deficient olefins bearing an allylic stereocenter, 4-8, are reported. The synlanti stereochemistry of the major endo adducts may be rationalized through the Houk transition-state model, but the possibility of intramolecular hydrogen bonding must be taken into account. In the case of the minor exo adducts the syn stereochemistry always predominates.
Synthesis of (+)-Methyl (R,E)-6-Benzyloxy-4-hydroxy-2-hexenoate and Its Mesylate Derivative
摘要:
Methyl (E)-6-benzyloxy-4-hydroxy-2-hexenoate is prepared in both racemic and enantiopure form through reaction between (2-benzyloxy)ethyloxirane and the dianion of phenylselenoacetic acid followed by esterification with diazomethane, oxidation to the selenoxide and subsequent pyrolysis in 72% overall yield.