Stereoselective Synthesis of Unnatural β-Amino Acids from Nitroethane via 5,6-Dihydro-4H-1,2-oxazin-3-ylacetates

Abstract

The reduction of easily available methyl 5,6-dihydro-4H-1,2-oxazin-3-ylacetates provides an efficient route to different diastereomerically pure unnatural β-amino acids. A two-step protocol including reduction of the C=N bond of the initial oxazine with sodium cyanoborohydride during the first step and hydrogenation of the N-O bond during the second step produced the target β-amino acid esters with higher stereoselectivity than obtained with conventional catalytic hydrogenation.

Key words

β-amino acids - 5,6-dihydro-4H-1,2-oxazines - reduction - hydrogenation - nitroethane

References

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12

When hydrogenation of 2a-g is carried out under milder conditions, significant amounts of products of partial reduction are formed; see ref. 11.