Oxidative Dimerization of Primary Alcohols

When the oxidation of a primary alcohol with PCC results in the formation of an aldehyde, activated with an electron withdrawing group at the a-position sometimes, a stable dimeric hemiacetal is formed that is further oxidized to a dimeric ester.331 This reaction, that can also happen with other chromium-based reagents (see page 42), can be minimized by adjusting the reaction conditions. 

The aldehyde reacts with the starting alcohol, yielding a stable hemiacetal that can be further oxidized to a dimeric ester. The formation of the dimeric ester can be minimized by the use of high dilution and the slow addition of the alcohol to the oxidant, resulting in a reaction giving an optimized 5 2 ratio of aldehyde to dimeric ester. 

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