Nickel boride desulfurization with

Aliphatic and aromatic sulfides undergo desulfurization with Raney nickel [673], with nickel boride [673], with lithium aluminum hydride in the presence of cupric chloride [675], with titanium dichloride [676], and with triethyl phosphite [677]. In saccharides benzylthioethers were not desulfurized but reduced to toluene and mercaptodeoxysugars using sodium in liquid ammonia [678]. This reduction has general application and replaces catalytic hydrogenolysis, which cannot be used [637]. 

Many other uses of a-sulfinyl carbanions are found in the literature, and in the recent past the trend has been to take advantage of the chirality of the sulfoxide group in asymmetric synthesis. Various ways of preparation of enantiopure sulfoxides have been devised (see Section 2.6.2) the carbanions derived from these compounds were added to carbonyl compounds, nitriles, imines or Michael acceptors to yield, ultimately, with high e.e. values, optically active alcohols, amines, ethers, epoxides, lactones, after elimination at an appropriate stage of the sulfoxide group. Such an elimination could be achieved by pyrolysis, Raney nickel or nickel boride desulfurization, reduction, or displacement of the C-S bond, as in the lactone synthesis reported by Casey [388]. 

Reduction and desulfurization of hetarenes with participation of nickel boride 970PP1. 

Thiophenes can also be desulfurized to alkenes (RCH2CH=CHCH2R from 115) with a nickel boride catalyst prepared from nickel(II) chloride and NaBILj in methanol.It is possible to reduce just one SR group of a dithioacetal by treatment... 

Partial desulfurization of disulfides to sulfides was accomplished by treatment with tris(diethylamino)phosphine in good yields [303]. 1,2-Dithiacy-clohexane was thus quantitatively converted to thiophane (tetrahydrothio-phene) at room temperature [303]. Complete desulfurization to hydrocarbons resulted when disulfides were refiuxed in ethanol with Raney nickel or nickel boride (yields 86 and 72%, respectively) [673]. 

Thiophenes can also be desulfurized to alkenes (RCH2CH=CHCH2R from 49) with a nickel boride catalyst prepared from nickel(II) chloride and NaBELj in methanol.It is possible to reduce just one SR group of a dithioacetal by treatment with borane-pyridine in trifluoroacetic acid or in CH2CI2 in the presence of AlCla. Phenyl selenides RSePh can be reduced to RH with Ph3SnH and with nickel boride. Cleavage of the C—Se bond can also be achieved with Sml2. ... 

A variation by Potts utilizes a-oxoketene ditioacetals in a condensation-cyclization bipyridine synthesis.49,50 For example, reaction of the Q-oxoketenc dithioacetal 3,3-bis(methylthio)-l-(2-pyridinyl)-2-propen-l-one with acetone and potassium /-butoxide, followed by treatment of the intermediate 1,5-enedione potassium salt, (9), with ammonium acetate produced the unsymmetric 6-methyl-4-(methylthio)-bpy, (10) (Scheme 5). Desulfurization with nickel boride afforded 6-methyl bipyridine in 72% yield. Various substituted bpys with alkyl and alkylsulfonyl groups were similarly produced in yields ranging from 37% to 94%. 

Truce has reported that a reagent prepared from nickel (II) chloride hexahydrate in ethanol by reduction with sodium borohydride and evidently similar to Brown and Brown s nickel boride can be used to effect desulfurization. Thus the diphenyl-... 

The subject of Raney nickel desulfurization has been exhaustively dealt with in CHEC-I. A few further interesting applications of this procedure will be presented in this section, along with the use of some nickel(O) complexes and nickel boride for this purpose. The major goal of understanding the mechanism of hydrodesulfurization by studying metal complexes as models is briefly dealt with in Section 2.10.6. 

Preferential desulfuration. In contrast to Raney-Ni, nickel boride permits preferential desulfuration with retention of sulfone groups. Despite lower yields nickel boride surpasses Raney-Ni in non-pyrophoric character and less hazardous use as well as in case of prepn. and accurate weighing. E. s. W. E. Truce and F. M. Perry, J. Org. Chem. 30, 1316 (1965). 

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