1.2- Oxaphospholenes formation

Treatment of the A -l,2-oxaphospholen (100 R ==OMe) with LiBr in MeOH yields the salt (101) together with the open-chain compounds (102) and (103) in the proportions 1 1 2. The formation of (102), and particularly the high yield of (103), has been advanced as good evidence for the participation of the intermediate (104), from which transfer of axial methyl group to Br occurs. ... 

The reaction of trimethyl phosphite with an allenic chloromethyl ketone proceeds with the formation of an oxaphospholene and not through the Michaelis-Arbuzov or Perkow rearrangements. ... 

A related route to 3-oxoalkylphosphonates involves the conjugate addition of trialkyl phosphites to a,P-unsaturated ketones and hydrolysis of the intermediate oxaphospholenes. The utility of this method is enhanced by the nucleophilic character of the intermediate oxaphosphorane, which facilitates the stereoselective aldol reaction resulting in the formation of p-substituted y-ketophos-phonates. - The pentacovalent oxaphospholene reacts with dialkyl azidocarboxylates to give P-hydrazido-y-ketophosphonates in excellent yields. ... 

Details have appeared of the formation of cyclopropanes from arylidene-malononitriles and the biacetyl-trimethyl phosphite adduct. 1,2-Oxaphospholens.— Among a 3-unsaturated ketones used in the formation of 1 1 adducts with tervalent phosphorus compounds are the sulphone (42) ... 

The usual product, after pyrolysis, is a 1,2-oxaphospholen 2-oxide (32), although an alcoholic work-up yields an acyclic phosphinate (33) (Scheme 10). Just in case these advances in our current mechanistic interpretation of these reactions (c/. ref. 40) leads to complacency, a further Russian paper has described the reactions of acetone and other simple ketones with chlorodiphenylphosphine or chlorodiethylphosphine. These yield the a-chloroalkylphosphine oxide (34), or the derived oxide (35), and not the oxide (36), which is known to be formed from mesityl oxide (28) and chlorodiethylphosphine. a-Halogenoalkylphosphine oxides are generally produced when aldehydes are heated with a wide range of halogenophosphines, and the formation of such an adduct from a ketone is a novel result. 

Reaction of the initially formed acylphosphonate with a second mole of trimethyl phosphite leads to the formation of a cyclic product with one pentacoordinated phosphorus atom. Further reaction of this oxaphospholene with a second molecule of butenoyl chloride, followed by the loss of methyl chloride, leads to the final product. ... 

Synthesis of Phosphonic and Phosphinic Acids and their Derivatives.—The usual batch of papers dealing with the C-phosphorylation of alkenes, 1,2-dienes, 2,3-dienes, and alkynes, - has appeared. Vacuum-dried sodium thiosulphate is an alternative to sulphur dioxide as the reagent for the decomposition of the intermediates formed in such reactions. Further examples of the formation of A -l,2-oxaphospholens from ketones and phosphonous dichlorides have been reported. ... 

Noteworthy, the formation of a six-membered ring is favoured over a seven-membered ring and the lack of rigidity in the substrate gave rise to oxaphospholenes (1). 

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