Tertiary arsine sulphides

The tetrahedral stereochemistry of a tertiary arsine sulphide was first established in 1925, when p-carboxyphenylethylmethylarsine sulphide (7) was resolved . Unlike hygroscopic tertiary arsine oxides, arsine sulphides are air-stable non-basic compounds with 

Some years later, two isomers of ethylene-l,2-bis(n-butylphenylarsine sulphide) (156) were isolated and were considered to be the racemic (R, R ) and the meso R, S ) 

The first synthesis of an optically active tertiary arsine sulphide from an optically active tertiary arsine was reported in 1962 , compounds 157 and 158 being prepared by heating the respective optically active tertiary arsines with sulphur in benzene. Along similar lines, arsine sulphides 136,159-164 were prepared and isolated (Table 8). The sulphurization of the tertiary arsines occurs with retention of configuration at arsenic. 

The optically active arsine sulphides 115, 119 and 121 (Table 8) were prepared by reactions between appropriate menthyl esters of thioarsinic acids and Grignard or alkyllithium reagents, which proceed with inversion of configuration at the arsenic(V) stereocentre. 

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TABLE 6. Tertiary arsines via esters of arsenic(V) acids and arsine sulphides... 

The optically active arsinous acid esters 128-134 and the arsinthious acid ester 135 have been used to prepare optically active tertiary arsines (Table 7). When the arsine sulphide 136 was heated in benzene with n-butyl or -propyl bromide, ethyl bromide was eliminated and there was a reversal in the sign of the rotation, which was attributed to the formation of the inverted n-butyl and n-propyl esters of (p-carboxyphenyl)phenyl-arsinthious acid, 137a and 137b, respectively (equation 18) . 

Under anhydrous conditions, however, optically active tertiary arsine oxides can be prepared from optically active tertiary arsines and dinitrogen tetraoxide. Thus, (-f- )-(p-carboxyphenyl)ethylphenylarsine [(-l-)-36] reacts with N2O4 in nitromethane to give a solution of (-I-)-(p-carboxyphenyl)ethylphenyIarsine oxide [(-l-)-147], which lost its optical activity over 1.5 h. The optically active arsine oxides 145,146,153 were similarly generated in solution (Table 8), but only racemates or racemic hydrochlorides were isolated . The oxides can also be prepared from the corresponding arsine sulphides... 

TABLE 8. Optically active tertiary arsine oxides and sulphides... 

The present phase in the development of the complex chemistry of the tertiary organic phosphines started in the early 1930s and was interrupted by the second World War. It is intimately connected with that of the corresponding arsines and sulphides and less so with the stibines, selenides, and tellurides—all being easier to prepare than the phosphines. 

Neutral nucleophiles are also alkenylated to give alkenylonium salts (Scheme 6). Examples include secondary amines (with concomitant deprotonation to afford enamines) and tertiary amines, acetic acid (with deprotonation to give alkenylacetates) formamides (that give alkenylformates), " sulphur-centred nucleophiles such as sulphides,thioamides (to give thioalkenes), thioureas and heterocyclic thiols group 15 nucleophiles triphenylphosphine, -arsine... 

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