Chiral lithiated phosphoric triamides: Structure, reactivity, and salt effects

The theoretical structure of a cyclic phosphoric triamide 3 and of its mono lithiated isomers 4-6 was calculated by ab initio methods (Fig. 1, Tables 1 and 2). The global minimum in 4 consists of a five-membered Li-C-N-P-O che late. The intermediates 5 and 6 are, relative to 4, energetically unfavorab le by 15 and 18 kcal mol(-1), respectively, due to distortion in order to a ccommodate the N-complexation of the Li+ ions. NMR Investigations (H-1, C-1 3, P-31, and Li-7) of the lithiated bicyclic phosphoric triamide 1 were per formed (Tables 3-5). The lithium aminomethanide 2 is characterized by a sp( 3)-hybridized anion supporting Li-C contacts. The anions exist in a monomer -dimer equilibrium in solution (Scheme 2). Trapping reactions of rac-2 with carbonyl compounds generated the corresponding amino-alcohol derivatives w ith high diastereoselectivities (Scheme 3, Table 6). A rational for the ste reochemical outcome is given (Fig. 4). In the presence of LiBr, a P-N bond cleavage occurred on reaction of rac-2 with aldehydes, which allowed the sy nthesis of (1-hydroxylalkyl)phosphonic diamides (Scheme 5, Table 7).