M. Tlahuextl et al., SYNTHESES, NMR-STUDY AND STEREOCHEMISTRY OF NEW P-H TRICYCLOPHOSPHORANES, Phosphorus, sulfur and silicon and the related elements, 123, 1997, pp. 5-19
Four new tricyclophosphoranes 1b-4b were synthesized derived from N,N'
-bis[2-hydroxy phenyl]ethylenediamine (1a), N,N'-bis[2-hydroxyphenyl]o
xamide (2a), N,N'-bis[(-)-norephedrine]ethylene (3a), N,N'-bis[(-)-nor
pseudoephedrine]oxalyl (4a), The syntheses of compounds 3b and 4b were
completely stereoselective giving only one epimer in each case (epime
r helix Delta, 3b; helix Lambda, 4b). For both the phosphorus configur
ation was established. The phosphorus atoms in 1b-4b adopt a trigonal
bipyramid geometry with an oxygen and a nitrogen atoms in apical posit
ions as deduced from P-31, C-13, H-1 and H-1/C-13 HETCOR NMR studies a
nd confirmed by the x-ray diffraction structure of 3b, Compound 1b rea
cts with BH3-THF giving the N-->BH3 adduct 1c; borane coordinates to t
he tetrahedral apical nitrogen atom. Compound 3b reacted with BH3 givi
ng two isomeric adducts, 3c and 3c'. The main product 3c came from att
ack of BH3 on the equatorial nitrogen followed by epimerization of the
phosphorus atom giving the molecule with the N-->BH3 group in an apic
al position and helicoidal structure Lambda. The minor isomer 3c' came
directly from addition of BH3 on an apical nitrogen atom giving the D
elta helix.