Synthesis of Aldehydes

The synthetic routes to aldehydes are probably more diverse and numerous than those to any other class of carbonyl compound, reflecting not only the intrinsic value of aldehydes as synthetic intermediates but also the scarcity of truly general routes to aldehydes themselves. As a result, a great number of relatively specific syntheses have been devised, often relying on partial oxidation or reduction procedures in which the danger of overreaction is always present. In contrast to such redox-based procedures, carbonylation chemistry offers a limited number of general synthetic routes to aldehydes which are both selective and high yielding, and often use readily accessible starting materials. The two must generally useful substrates for carbonylative aldehyde synthesis are halocarbons and alkenes, and a number of catalytic or stoichiometric reactions will be described that allow the synthesis of a wide variety of functionalized aldehydes under relatively mild conditions.