Chemistry of the 2,3‐oxaphosphabicyclo[2.2.2]octene ring system: Extrusion of metaphosphates

Abstract

These fragmentations were accomplished thermally (110" in toluene). We later found that the fragmentations could be conducted at room temperature by subjecting the precursors to ultraviolet light (254 nm) [2], and we generated both alkyl metaphosphates and N,N-dimethylmetaphosphoramidate (Me2N-P02) by this method. Other studies have led to the generation of alkyl metathiophosphates [3]; applications of the 3-coordinate species for special phosphorylations have also been described [4]. We have continued to develop the chemistry of the 2,3-oxaphosphabicyclo[2.2.2]octene ring system, and we report in this paper some new observations on the synthesis and stereochemistry of the system, as well as on some kinetic studies of the thermal fragmentation that provide compelling proof that a free metaphosphate is indeed released. Additional proof for a free metaphosphatt, has come from the use of chiral P-alkoxy derivatives of the bridged ring system, which are useful in proving the planarity of the species, but also reveal that an oxy function properly placed may undergo anchimeric participation with the metaphosphate function.In Scheme 1 is outlined the general synthetic method used for the construction of the requisite ring system. Phosphole oxide intermediates are first generated and instantly trapped by Diels-Alder reaction with a maleimide derivative to give a product with the 7-phosphanorbornene framework. No other dienophile has yet been found to be superior 0 1991 VCH Publishei-s, Inc

Steric hindrance in the synthesis and properties of the dimer of 1-(2,4,6-Tri-tert-butylphenyl)phosphole 1-oxide

“…The 3,4-dimethylphosphole oxides seem to be more stable than the monomethyl species; the dimethyl-1-phenyl derivative remained unchanged for a few hours at room temperature [6].…”

Competitive [4 + 2] cycloadditions in equimolar mixtures of 1‐arylphosphole oxides

“…In some cases, especially those in which a sterically demanding trialkylphenyl substituent is bonded to the phosphorus atom, it was possible to detect the phosphole oxide intermediates in the reaction medium [6][7][8]. In the presence of dienophiles such as N-phenylmaleimide, the phosphole oxides were efficiently trapped [2].…”

Dimethyl Acetylenedicarboxylate and Phospholes: A Variety of Reaction Pathways

“…Indeed, when mixing the phosphole and the excess amount of DMAD in dichloromethane, two peaks appear in the 31 P NMR spectrum at δ = 19.6 and 40.7 ppm. The first one corresponds to 3a, whereas the second one corresponds to the monomeric phosphole oxide [7] that slowly disappears by [4+2] dimerization (δ = 52.5 and 74.1 ppm, J P,P = 39.6 Hz). To better understand the chemistry of initially formed [1+2] adduct 2a, we decided to perform a DFT study of model compound 4 at the B3LYP/6-311+G(d,p) level.…”