Hydroxy amines from alkenes

The reaction of aryl azides with excess alkenes in the presence of trifluoroacetic acid proceeds by an analogous mechanism and afforded, after basic hydrolysis, /5-hydroxy amines together with byproducts. A diastereoselective reaction was observed only with cyclic and acyclic (Z/-alkenes, e.g., 12 and 1388. From methyl ( )-2-butenoate, A-phenylthreonine methyl ester was similarly prepared in 30% yield88. 

Acetals result from oxidative coupling of alcohols with electron-poor terminal olefins followed by a second, redox-neutral addition of alcohol [11-13]. Acrylonitrile (41) is converted to 3,3-dimethoxypropionitrile (42), an intermediate in the industrial synthesis of thiamin (vitamin Bl), by use of an alkyl nitrite oxidant [57]. A stereoselective acetalization was performed with methacrylates 43 to yield 44 with variable de [58]. Rare examples of intermolecular acetalization with nonactivated olefins are observed with chelating allyl and homoallyl amines and thioethers (45, give acetals 46) [46]. As opposed to intermolecular acetalizations, the intramolecular variety do not require activated olefins, but a suitable spatial relationship of hydroxy groups and the alkene[13]. Thus, Wacker oxidation of enediol 47 gave bicyclic acetal 48 as a precursor of a fluorinated analogue of the pheromone fron-talin[59]. 

A highly enantioselective Baylis-Hillman reaction based on the combined use of an activated alkene (23) and a chiral amine catalyst (QDA) derived from cincho-nane has been developed. The reaction permits the conversion of a wide variety of aldehydes to the corresponding a-methylene-jS-hydroxy esters (28) with high ee in reasonable yields. 

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