1.3- Alkadienephosphonic dialkyl esters

On using 3,3-disubstituted-l,2-alkadienephosphonic dialkyl esters as the substrates in the above discussed reaction, a mixture of dialkyl esters of the 1,2-oxa-phospholic acid and 1,2-adducts was obtained. The products ratio depends on nature of the substituents at the substrate, and on the polarity of the solvent (Scheme 41) [103, 104],... 

The 1,2-alkadienephosphonic dialkyl esters react smoothly with dialkoxyphos-phonylsulphenyl chlorides, affording 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives 126 (Scheme 52) [117],... 

The target compounds were also obtained from the reaction of 2-chloro-l,3-alkadienephosphonic dialkyl esters with areneselenenyl chlorides (Scheme 82) [159],... 

Dihydro-l,2-oxaphosphole-2-oxide derivatives were the main products obtained from halogenation of dialkyl esters of 1,2-alkadienephosphonic acids (Scheme 37) [53, 69, 79, 81, 93-100],... 

As underlined above, formation of these compounds by halogenation of dialkyl esters of 1,2-alkadienephosphonic acids is the major direction of the reaction. Even in the case of dialkyl esters of propadienephosphonic acid, some 1,2-oxaphosphole derivatives could be detected [86], On using sulfuryl chloride as electrophilic reagent, only 3,3-disubstituted- and 3-monosubstituted substrates could be transformed in oxaphosphole derivatives [39], Thus, the main role of the substituent at the C3 atom of the allenephosphonate system, for the formation of 2,5-dihydro-l,2-oxa-phosphole-2-oxide derivatives, was demonstrated. 

Compounds 118 could be produced from the reaction of dialkyl esters of 3-monosubstituted-l,2-alkadienephosphonic acids with methylselenenyl chloride. It was established that, along with 118, 2,3-adducts were also formed [113]. Use of phenylsulphenyl chloride in this reaction leads exclusively to the formation of 2,5-dihydro- l,2-oxaphosphole-2-oxide derivatives 117 (Scheme 48) [113, 114]. 

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