New approaches to the synthesis of vitamin D metabolites. 2. Effect of some substituents on stereochemistry in the intramolecular cycloadditions of nonatrienes
Abstract A simple one-pot process for in situ bromination of (ethoxycarbonylmethylene)-triphenylphosphorane 1 was carried out. This was followed by oxidation of alcohol using SO3. Pyridine complex as a mild oxidant and in situ trapping of the aldehyde. This process constitutes a stereoselective one-pot procedure for the preparation of Z-configured α-bromo-α, β-unsaturated esters in good yield. GRAPHICAL
in CH2Cl2 followed by the addition of an alcohol in the presence of manganese dioxide under ultrasonic irradiation constitutes a stereoselective one-pot procedure for the preparation of Z-configured α–bromo-α,β-unsaturatedesters in good to excellent yield.
Palladium-mediated reductive coupling, a stereoselective approach to the 8-dehydropumiliotoxin skeleton
作者:Stephanie A. Feutran、Helena McAlonan、Paul J. Stevenson、Andrew D. Walker
DOI:10.1016/j.tetlet.2009.03.122
日期:2009.7
Reductive cyclisation of an E-vinyl bromide with an allylic acetate proceeds under palladium catalysis to give the 8-dehydropumiliotoxin skeleton, a potential advanced precursor to 8-deoxypumiliotoxin alkaloids. Control of the stereochemistry of the E-vinyl bromide precursor is achieved readily using the Kogen or Bruckner bromophosphonate reagents and the reductive cyclisation proceeds with retention