Thioalkoxides

Alkoxide-Type Initiators. Using the guide that an appropriate initiator should have approximately the same stmcture and reactivity as the propagating anionic species (see Table 1), alkoxide, thioalkoxide, carboxylate, and sUanolate salts would be expected to be usehil initiators for the anionic polymeri2ation of epoxides, thikanes, lactones, and sUoxanes, respectively (106—108). Thus low molecular weight poly(ethylene oxide) can be prepared... 

Halide displacement by thioanions such as thioalkoxides, thiocyanate and sulfite, can be readily carried out under PTC conditions in activated arenes. The reaction of nitro- and dinitro-aryl halides with thiophenol and NaOH in the presence of an ammonium or phosphonium salt catalyst proceeds readily in toluene at room temperature to give the phenyl aryl sulfides in nearly quantitative yield.189 Excellent yields of thiocyanoarenes were obtained from the reaction of the 2,4-dinitrohalobenzenes with KSCN in toluene at 90 C with a tetraalkyl onium salt PTC catalyst.190... 

The usual substitution pathway for activated olefins is illustrated by Scheme 34 regarding anionic nucleophiles. In 73, R1 and R2 are electron-attracting groups L is the leaving group (usually a halogen atom) and Y is the charged nucleophile (in particular, alkoxides and thioalkoxides). 

The cyclic dialkyltin thioalkoxides, R2SnSC S, are, like their acyclic counterparts, unassociated monomeric species in solution and, accordingly, show high-frequency 1,9Sn signals. (63, 65, 71)... 

Here the subsequent oxidation can be neglected, and the products were readily separated by distillation. Again, low yields of triester were obtained when equivalent quantities of thioalkoxide and phosphorus were used. Evidence of incomplete conversion was obtained from the 31P NMR spectra of the reaction mixtures using... 

The two intermediates probably arise in the later stages of the reaction when the thioalkoxide concentration is low. The presence of these intermediates is evidence of the intermediate formation of the trichloromethyl anion, in reactions of the following kind. 

These reactions occur because the thioalkoxide is depleted by reaction with tetrachloromethane in the following side reactions ... 

With two equivalents of thioalkoxide, the triester only is produced and this can be distilled from the reaction mixture in high yield (e.g. 97% from ethanethiol and 82% from butanethiol). 

Intramolecular attack of a terminal thioalkoxide function, generated by the action of MeLi on the d -acetyl group, at the 4-position of the diastereomerically pure, TMS-protected 2-phenyloxetan-3-ol 468 results in cleavage of the 4-membered ring and formation of tetrahydrothiopyran-3-ol. The stereochemistry at C-2 and C-3 of the oxetane is retained in the product (Equation 154) <1996JOC7642, 1998JOC1910>. 

The semipolar Sb—S bond may easily allow formation of trimethylanti-mony halide thioalkoxide (XII) via a four-centered intermediate (XI). 

The difference in stability between compounds XII and XIII may be attributed to a less reactive Sb—S bond in XIII. This is consistent with the fact that trimethylantimony bis (thiocarboxylates) is thermally more stable than the bis(thioalkoxides) 33, 34). 

The ligands that have been used in the preparation of metal nitride complexes are quite varied. They include halides, carbogenic groups (alkyl moiety and Cp ), pnic-togens (amine, amide, imide, phosphine, and arsine), and chalcogens (ether, alkox-ide, oxo, thioalkoxide, and selenides). Chart 1 provides a listing of the various ligands and the associated nitrido metal complexes. 

Nitrido molybdenum complexes have been reported for MoVI, Mov, and MoVI. Among these, MoVI nitrides have been the most extensively studied. For the other two classes of nitrido molybdenum complexes, phosphine and thioalkoxide ligands are common, as they are suggested to stabilize the lower oxidation states through n-back bonding. 

Soft nucleophiles (Nu) generally give the best results so, for carbon-carbon bond formation, stabilized enolates such as malonates are best, but for C-X (X = O, N, S) bond formation the reaction is successful with alkoxides, amines, cyanide, and thioalkoxides. This example shows an amine attacking outside the ring probably because the alkene prefers to be inside the ring. 

The formation of enol ethers and thioethers via coupling between a vinyl bromide and a tin alkoxide or thioalkoxide has been reported by Rossi et al. [205J. Two detailed papers [206,207] have appeared concerning the formation of tertiary aromatic amines via coupling of Bu3SnNMe2 and aromatic systems mechanistic studies are reported. 

They also described the reaction of the diacetate (272) with base, to give (273), a reaction that emphasizes the powerful neighboring-group abihty of the thioalkoxide ion to eject acetate ion, a poor leaving-group. The conversion of the epoxide (268) into the episulfide (267) by thiourea was also reported.As was pointed out by Bordwell and Andersen, the... 

---