The theoretical structure of a cyclic phosphoric triamide 3 and of its monolithiated 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 chelate. The intermediates 5 and 6 are, relative to 4, energetically unfavorable by 15 and 18 kcal mol−1, respectively, due to distortion in order to accommodate the N-complexation of the Li+ ions. NMR Investigations (1H, 13C, 31P, and 7Li) of the lithiated bicyclic phosphoric triamide 1 were performed (Tables 3 – 5). The lithium aminomethanide 2 is characterized by a sp3-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 with high diastereoselectivities (Scheme 3, Table 6). A rational for the stereochemical 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 synthesis of (1-hydroxylalkyl)phosphonic diamides (Scheme 5, Table 7).
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Müller et al. (1999) studied this question.