Grignard Addition to Aldonitrones. Stereochemical Aspects and Application to the Synthesis of C2-Symmetric Diamino Alcohols and Diamino Diols

A new example of the stereoselective installation of the amino group at a saturated carbon center via organometallic addition of chiral aldehydes to nitrones is illustrated by the synthesis of 1,3-diamino propanol 1 and 1,4-diamino butandiol 2 units. Three diamino alcohol 1 stereotriads were obtained by stereoselective addition of alkylmagnesium halides (benzyl, cyclohexylmethyl, and metallyl) to the N-benzyl nitrones derived from β-amino-α-hydroxy aldehydes followed by reduction of the resulting N-benzylhydroxylamines. Three 1,4-dibenzyl substituted stereoisomers of type 2 with fixed S configuration at C2 and C3 were prepared by sequential and simultaneous amination in two directions starting from l-threose nitrone and l-tartraldehyde bis-nitrone, respectively. The R,S,S,R isomer obtained by the former route was converted into a seven-membered ring cyclic urea (1,3-diazapin-2-one), i.e., a compound that belongs to a class of nonpeptide HIV-1 protease inhibitors.