Davy s reagent methyl

Bis-(methylthio)-l,3,2X, ,4X, -dithiadiphosphetane-2,4-dithione (Davy s reagent methyl)... 

Bis(methylthio)-l,3,2X, 4A, -dithiadiphosphetane-2,4-dithione (Davy s reagent methyl) [82737-61-9] M 284.4, m 160°. It crystallises from C6Hg in yellow plates or from hot trichlorobenzene. The low melting point reported in the literature (112° with gradual softening at 68-102°) has been attributed to the presence of elemental sulfur in the crystals. It has a foul odour and is a suspected carcinogen. [Yousif et al. Tetrahedron... 

Conversion of propanoic acid into methyl propanedithioate with Davy s reagent (R2 = Me)... 

A solution of propanoic acid (5.92 g, 80mmol) in 1,2,4-trichlorobenzene (80 ml) was heated at 80-100°C. Davy s methyl reagent (12.6 g, 44 mmol), prepared according to [142], was added portionwise in 2 min. The mixture was heated at 140°C during 10 min (caution operate under a hood and trap obnoxious vapours by bleach). It was then cooled to room temperature. The liquid which separated was distilled to give yellow methyl propanedithioate (5.93 g, 49 mmol, 61%), b.p. 57°C/12 torr. 

S. Davies has used an iron complex as an auxiliary for the asymmetric cyclopro-panation of a,P-unsaturated carbonyls [105]. The iron acyl is most stable in the s-cis conformation, as illustrated in Scheme 6.27, in order to avoid severe interactions between the iron ligands and R. Coordination of the Simmons-Smith reagent to the carbonyl oxygen, anti to the iron, forces the alkene moiety out of conjugation and approximately orthogonal to the carbonyl. Because of the bulky triphenyl phosphine in the rear, this rotation can only be towards the front. Transfer of the methylene via the illustrated transition state accounts for the observed diastereoselectivity. Oxidation with bromine removes the iron acyl and derivatization with a-methyl-benzyl amine allowed evaluation of the stereoselectivity. 

---