The Ligand‐Exchange Process of P–H_apical Phosphoranes and the Thermal Formation and Pseudorotation of Anti‐Apicophilic Spirophosphoranes

Abstract

Monocyclic P–Hapical phosphoranes 10 bearing a ring‐opened Martin ligand are formed upon treatment of the P–Hequatorial spirophosphorane 7 with more than 2 equiv. of alkyllithium compounds. A ligand‐exchange process of these phosphoranes 10 involving the interconversion of the bidentate Martin ligand with the monodentate Martin ligand was found to proceed, probably through a hexacoordinate phosphorus atom. Heating of 10 in nondonating solvents furnished alkylspirophosphoranes 5, whereas heating of 10 in donor solvents led to the formation of anti‐apicophilic phosphoranes 6, a new class of phosphoranes in which the less apicophilic carbon substituent occupies an apical position and the more apicophilic oxygen atom occupies an equatorial position. These phosphoranes 6 were found to completely convert into their energetically more stable Cequatorial,Oapical stereoisomers 5 upon heating. On the basis of kinetic examinations of the cyclization process of 10, the formation of 6 can be rationalized by the enhanced nucleophilicity of the hydroxy group in the donor solvents. The isomer 5b was estimated to be more stable than 6b (R = nBu) by 12 kcal mol–1 from kinetic studies on the pseudorotation of 6b to 5b. This is in good agreement with theoretical calculations with analogous 5a and 6a (R = Me), which estimate the difference in energy to be 14.1 kcal mol–1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A New Method for the Formation of Anti‐apicophilic (O‐cis) Spirophosphoranes – Kinetic Studies on the Stereomutation of O‐cis Arylspirophosphoranes to Their O‐trans Isomers

“…[5,7] However, for the O-cis 2,6-dialkylphenyl derivatives, 19 F NMR spectra of the crude products after workup at room temperature showed either three (2i-l) or four signals (2m, n), indicating the presence of a slower corresponding BPR process for the 2,6-dialkylphenyl derivatives. This should be a consequence of the steric hindrance exerted by the ortho alkyl groups as evident from the decelerated P-C bond rotation (vide supra).…”

“…[15] Additionally, the equatorial P-O bond of 2n (1.678 Å) was somewhat longer than those of alkyl derivatives 2b (1.658 Å) and 2c (1.652 Å), despite the apical P-O bond length of 2n (1.777 Å) being comparable to those of the alkyl derivatives 2b (1.773 Å) and 2c (1.771 Å). [7] Thus, the distortion from TBP geometry of 2n and 3n does not follow any pseudorotation process. This is [a] Pivot: C10.…”

“…and ∆S ‡ = -9.0 eu), [7] indicating that significant modification is required to make the apicophilicity of aryl groups comparable with alkyl groups. The use of AcOH as solvent did not lead to a significant increase in rate.…”

“…The synthesis of 2a-c was accomplished via thermal cyclization reactions of P-H (apical) monocyclic phosphoranes 1a-c (Scheme 1) in pyridine. [7] In order to gain a compreScheme 1.…”

Reaction of 5-oxo-2-phenyl-4,4-bis(trifluoromethyl)-4,5-dihydro-1,3,2-benzodioxaphosphepine with chloral. The synthesis and spatial structure of 5-carbaphosphatrane containing a four-membered ring

“…That is why their synthesis, reactivi ties, and configurational stabilities are under intensive study. [1][2][3][4][5][6][7][8][9][10][11][12] The benzodioxaphosphole fragment stabilizes the pentacoordinated state of phosphorus most efficient ly. 5 Taking this into account, we have proposed a new approach to the preparation of phosphoranes that involves reactions of activated carbonyl compounds with benzo dioxaphospholes containing the tricoordinated P atom and a carbonyl or imino group in the γ or δ position relative to the P atom in the endocyclic substituent.…”