PENTACOORDINATED MOLECULES .84. CONFORMATIONAL EFFECTS OF RING FUSION AND HETEROATOM SUBSTITUTION IN 6-MEMBERED RINGS OF SPIROCYCLIC OXYPHOSPHORANES

Spirocyclic oxyphosphoranes containing six-membered rings 1-5 were synthesized by oxidative addition of cyclic phosphites with phenanthrenequinone. Substituent variations in 1-5 allowed the examination of the conformational stability of the six-membered ring system. This ring in 4 was trans annelated with cyclopentane, established by X-ray analysis. The latter feature has relevance to c-AMP. A cis-fused phosphorinane derivative containing a furanose ligand 7 was also prepared. X-ray structures revealed trigonal-bipyramidal frameworks with the phosphorinane ring occupying apical-equatorial positions. The saturated six-membered ring was uniformly in a boat conformation. Despite considerable electronegativity and ring substituent effects, no diequatorial ring placement was evident. Variable-temperature H-1 NMR data indicated retention of solid-state structures in solution. Rapid pseudorotation is indicated for the various phosphoranes with the thio derivative 2 appearing more fluxional. Analogies with models for cyclic AMP action are discussed. Phosphorane 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 7.769 (2) angstrom, b = 10.191 (2) angstrom, c = 29.594 (5) angstrom, and Z = 4. The thiophosphorane 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 7.696 (1) angstrom, b = 10.441 (2) angstrom, c = 30.130 (6) angstrom, and Z = 4. The diaminophosphorane 3 crystallizes in the triclinic space group Pl with a = 10.078 (3) angstrom, b = 10.133 (3) angstrom, c = 12.253 (3) angstrom, alpha = 101.60 (2)-degrees, beta = 92.81 (2)-degrees, gamma = 105.00 (2)-degrees, and Z = 2. The fused-ring phosphorane 4 crystallizes in the monoclinic space group P2(1)/c with a = 15.147 (3) angstrom, b = 9.092 (2) angstrom, c = 18.089 (4) angstrom, beta = 108.92-degrees, and Z = 4. The final conventional unweighted residuals are 0.037 (1), 0.036 (2), 0.040 (3), and 0.040 (4).