Phospholene 2-sulphides

The A3-phospholen sulphides (44), bearing reactive functional groups, may be reduced to the phosphine using nickelocene in the presence of allyl iodide.37 The intermediate nickel complex is decomposed with cyanide to free the functionalized A3-phospholen (45). 

Endocyclic enamines may be combined with / -functional groups leading to cyclic /2-phospholene sulphide enamines130 (60), cyclic /2-ketoenamines131,132 (61), 3-(pyrrolidi-n-l-yl)-5,6-dihydro-4//-thiopyran 1,1-dioxide133 (62) and 3-amino-5,6-dihydro-4//-pyran134 (63). 

The dibenzophosphonin (332) has been synthesized by the oxidative photo-cyclization of l,3,4-triphenyl-3-phospholene oxide (333). Photofragmentation is observed, however, on irradiation in methanol of 3,4-dimethyI-3-phospholene sulphide (334) to give the diene (335) and 0-methyl phenylphosphinothioate (336)... 

Assignments. - Electric modulation of vibrational rotational bands of polar molecules included a study of phosphine.120 Ringbending (puckering) transition frequencies have been measured for the phospholene (42) for the ground and excited states.121 The PD deformation band for the sulphide (43) has been assigned.122... 

Further examples of deoxygenation of epoxides by phosphine sulphides or selenides have appeared,41 as shown in Scheme 6 for simple epoxides (50). Incorporation of phosphorus into a five-membered ring appears to be responsible for the relatively rapid deoxygenations by the phosphole and A3-phospholen derivatives.41... 

Hydrolysis of the cycloaddition products of chlorophosphines with dienes has been a popular route to phospholen 1-oxides. " These sequences usually lead > to epimeric mixtures (at phosphorus), as illustrated for the preparation of the oxides (8), (9), (10), (13), and (14) shown in Schemes 2 and 4 . When hydrogen sulphide is used as a quenching agent, forming the sulphides (11) and (12), much greater stereoselectivity is observed (Scheme 3). ... 

PhosphoIene sulphides (IS) and oxides have been prepared by [1+4] cycloaddition reactions of (14) with various dienes. Phosphorus analogues (17) and (19) of erythrofuranose have been prepared by stereospecific ci.y-hydroxylation of the 2-phospholene-l-oxides (16) and (18), respectively.Compounds (17) and (19) readily epimerise at C-2 on treatment with base. 

Other reactions between cyclic phosphorochloridites or cyclic esters and dienes are summarized in Scheme here, A and B are O, S or Se, and may be different or identical, and X = Cl, Br, NCS, or OR, and the conversion is brought about when mixtures of reactants are heated together in sealed tubes for extended time periods. As in the many examples known in which the reacting system, as a whole, is sulphur-free, the nature of the intermediate can be in doubt, and probably depends on the nature of the substituents, particularly those directly connected to phosphorus thus some reactants may interact through a covalent, pentacoordinate species 27, whereas others form a pseudoquatemary intermediate 28. It may also be that one intermediate structure is transformed into the second before the ultimate formation of the 3-phospholene (29). Also, in accord with these ideas, thiophosphorus(III) halides have been obseved to react with a,j5-unsaturated ketones to give, ultimately, l,2-oxa-4-phospholenes as their 2-sulphides (30) (Scheme 3)45 8. reactions carried out in acetic acid solution the products are said to be the esters... 

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