NADH model studies. Part 2. Cationic hydrogenations using acridan derivatives as hindered NADH models

Abstract

Various aryl alcohols (5), arylethylenes (6), and trityl ethers (7) are found to undergo smooth reduction in dichloromethane at room temperature when treated with an equimolar amount of the acridans (3) and trifluoroacetic acid. The limiting acidity value (H₀) for the medium in which the compounds (3) are completely protonated and hence not suitable as NADH models was also determined spectrophotometrically. Kinetic studies of reduction of (5) with (3) in dilute sulphuric acid, or Hantzsch ester (2) in glacial acetic acid, indicated that during reduction steric hindrance is important in less acidic media whereas the reduction of cations performed with trifluoroacetic acid is not affected by steric factors.