Synthesis of syn- and anti-1,2-amino alcohols by regioselective ring opening reactions of cis-3-aminooxetanes

N-t-Butyloxycarbonyl (Boc) substituted cis-2-phenyl-3-aminooxetanes 3 undergo a ring expansion to oxazolidinones 5 upon treatment with trifluoroacetic acid. The reaction occurs at the C(2) position under inversion of configuration. Alternatively, 3-aminooxetanes can be ring-opened at the less substituted C(4) position with retention of the relative configuration between C(2) and C(3) as exemplified by the synthesis of (+)-pseudoephedrine (2). The cis3-aminooxetanes serve as precursors for either syn- or anti-1,2-amino alcohols.