Model studies of the reduction of 3-phenyl-6H-1,2-oxazines, chemo- and stereoselectivity: synthesis of amino alcohols, amino acids, and related compounds

Synthesis of 1,2-amino alcohols via catalytic C–H amidation of sp3 methyl C–H bonds

A new route to 1,2-amino alcohols is presented by C–H amidation of sp³ methyl C–H bonds as a key step. Various alcohols were employed after converting them to removable ketoxime chelating groups. Iridium-catalyzed C–H amidation and following LAH reduction furnished β-amino alcohol products.

Palladium-catalyzed cross coupling reactions of 4-bromo-6H-1,2-oxazines

A number of 4-aryl- and 4-alkynyl-substituted 6H-1,2-oxazines 8 and 9 have been prepared in good yields via cross coupling reactions of halogenated precursors 2, which in turn are easily accessible by bromination of 6H-1,2-oxazines 1. Lewis-acid promoted reaction of 1,2-oxazine 9c with 1-hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines.

The first catalytic inverse-electron demand hetero-Diels–Alder reaction of nitroso alkenes using pyrrolidine as an organocatalyst

The first catalytic inverse-electron demand hetero-Diels-Alder reaction of nitroso alkenes has been developed. Nitroso alkenes were generated in situ from alpha-halooximes and underwent [4 + 2]-cycloadditions with enamines as dienophiles formed from aldehydes and pyrrolidine (10 mol%) as an organocatalyst. The presence of a suitable heterogeneous buffer system was found to be essential and best results were obtained with sodium acetate trihydrate. The resulting 5,6-dihydro-4H-oxazines were obtained in moderate to good yields under mild reaction conditions. A catalytic cycle has been proposed and evidence for the cycloaddition mechanism has been obtained. Moderate asymmetric induction (42% ee) was observed when a chiral secondary amine was used.