Conformational Effects of Ring Fusion and Heteroatom Substitution in Six-Membered Rings of Spirocyclic Oxyphosphoranes

Abstract

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 1H 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 P212121 with a = 7.769 (2) Å,b= 10.191 (2) Å, c = 29.594 (5) Å, and Z = 4. The thiophosphorane 2 crystallizes in the orthorhombic space group P212121 with a = 7.696 (1) Å, b = 10.441 (2) Å, c = 30.130 (6) Å, and Z = 4. The diaminophosphorane 3 crystallizes in the triclinic space group P[formula omitted] with a = 10.078 (3) Å, b = 10.133 (3) Å, c = 12.253 (3) Å, a = 101.60 (2)°, β = 92.81 (2)°, γ = 105.00(2)°, and Z = 2. The fused-ring phosphorane 4 crystallizes in the monoclinic space group P21/c with a = 15.147 (3) Å, b = 9.092 (2) Å, c = 18.089 (4) Å,β= 108.92°, and Z = 4. The final conventional unweighted residuals are 0.037 (1), 0.036 (2), 0.040 (3), and 0.040 (4). © 1991, American Chemical Society. All rights reserved.