反应详情

A synthetic scheme that is particularly useful for preparation of aldehydes of formula III where n is 3 or 4 and A is 2,5-thienylene or 2,5-furylene is illustrated by the method of synthesis of methyl 5-(4-oxobutyl)thiophene-2-carboxylate (XXII): ##STR36## an aldehyde of formula II where A is 2,5-thienylene, n is 3, and R8 is methyl. Here, the dianion prepared by the action of lithium diisopropylamide on 5-methylthiophene-2-carboxylic acid is alkylated with 3-(tetrahydro-2H-pyran-2-yloxy)propyl iodide. The product of alkylation is esterified with methyl iodide and potassium carbonate and the THP protecting group removed by acid-catalyzed hydrolysis to give methyl 5-(4-hydroxybutyl)thiophene-2-carboxylate. Oxidation of the primary alcohol functional group with chromium trioxide affords the aldehyde intermediate XXII.

1. customremoved by acid-catalyzed hydrolysis