Secondary allylic alcohols, occasional

Sometimes, tertiary allylic alcohols interfere with the oxidation of primary and secondary alcohols with PDC, causing low-yielding transformations into the desired aldehydes and ketones.161 Secondary allylic alcohols occasionally suffer oxidative transposition to enones rather than a direct oxidation.162... 

Quite a number of transition-metal complexes are capable of isomerizing allyUc alcohols into transition-metal-enol complexes through an internal redox process. Those can then be trapped in situ with aldehydes in an aldol reaction. Motherwell and coworkers developed a RhClIPPhjIj-catalyzed domino isomerization-aldol reaction of secondary allyl alcohols, which gave rise to a mixture of syn- and owti-aldol products, with only small amounts of the regioisomeric aldol product occasionally being formed (Scheme 8.25) [42]. 

Yields of the primary alkyl acrylates vary somewhat, owing to occasional losses through formation of polymer, but are usually in the range of 85-99%. Some secondary alcohols react very slowly, others readily. The method has been applied to more than fifty alcohols, some of which (with percentage yields) are listed below ethyl, 99% isopropyl, 37% -amyl, 87% isoamyl, 95% -hexyl, 99% 4-methyl-2-pentyl, 95% 2-ethylhexyl, 95% capryl, 80% lauryl, 92% myristyl, 90% allyl, 70% fur-furyl, 86% citronellyl, 91% cyclohexyl, 93% benzyl, 81% (3-ethoxyethyl, 99% /S-(/3-phenoxyethoxy) ethyl (from diethylene glycol monophenyl ether), 88%. 

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