Diphosphane dioxide

An intense search for further three-membered rings with two heteroatoms has been successful during recent years. 1,2-Di-r-butyldiphosphirane (10) was synthesized from the potassium compound of a diphosphane with 2,2-dichloropropane <78ZN(B)1208). Azaphos-phiridine (11) (81AG(E)385) and oxaphosphirane (12) (78CB3105) have been described, as was the thiaziridine dioxide (13) which wafs stable at — 30 °C (80H(14)1677). A C—P—S three-membered ring (1,2A 5-thiaphosphirante) was also obtained recently (81CC72). 

The turnover frequency (TOF = mole of product per mole of catalyst per hour) of this rapid reaction is rather high, with values up to 1400. This reaction, carried out at 50 °C in SC-CO2, is 18 times faster than in conventional tetrahydrofuran under otherwise identical reaction conditions. This formic acid synthesis can be coupled with subsequent reactions by addition of methanol or dimethylamine, this supercritical reaction system provides a highly efficient one-pot route to methyl formate and A,A-dimethylforma-mide, respectively [918]. Another example of a reaction in which carbon dioxide acts as both reactant and reaction medium is the formation of tetraethyl-2-pyranone from hex-3-yne and CO2 in the presence of an Ni(II)-diphosphane catalyst at 102 °C under supercritical reaction conditions [919]. 

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