Phospholes oxaphosphole

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. 

A similar procedure was followed for the preparation of 2,5-dihydro-l,2-oxa-phosphole-2-oxide derivatives 134 possessing CH2OH group at C3 atom of the oxaphosphole ring. The oxaphosphole products were obtained as E/Z mixture from the reaction of l-substituted-l,2-alkadienephosphonic diethyl esters 135 with halogens (Scheme 54) [121, 122],... 

The phenylphosphonic acid 197 reacts with 5 equiv. of AgC104 to deliver the 1,2-oxa-phosphol-3-ene-2-oxide 198 in an 80% total yield of the Z- and E-isomers (Scheme 15.63) [127]. For related reactions, see also [128]. With a phosphonic acid and Hg(OAc)2, the mercurated intermediate, a 4-acetoxymercury l,2-oxaphosphol-3-ene and the corresponding chloride after ligand exchange were isolated [129]. 

The heterocycles that are discussed in this chapter are 1,3-heterophospholes (which include 1,3-diphospholes, by far the most studied) and 1,3-heteroarsoles, specifically 1,3-azaphospholes 1 and 5, 1,3-oxaphosphole 2, 1,3-thia-phosphole 3, 1,3-selenaphosphole 4, 1,3-diphosphole 6, the 1,3-diphospholyl anion 7, 1,3-azarsoles 8 and 12, 1,3-thiarsole 9, 1,3-selenarsole 10, and 1,3-phospharsoles 11 and 13. 

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