Reductive desulfurization Thioethers

Controlled reductive desulfuration Thioethers from mercaptals C(SR)2 -> CH(SR)... 

Controlled reductive desulfuration Thioethers from mercaptals... 

An interesting Fe-catalyzed SN2 -like carbene insertion reaction using diazo compounds and allyl sulfides (the Doyle-Kirmse reaction) was reported by Carter and Van Vranken in 2000 [20], Various allyl thioethers were reacted with TMS-diazomethane in the presence of catalytic amounts of Fe(dppe)Cl2 to furnish the desired insertion products with moderate levels of stereocontrol [Equation (7.6), Scheme 7.14]. The products obtained serve as versatile synthons in organic chemistry, e.g. reductive desulfurization furnishes lithiated compounds that can be used in Peterson-type oleftnations to yield alkenes [Equation (7.7), Scheme 7.14] [21]. 

Reductive desulfurization of the dithioketals 5.14 and 5.15 is performed under the same conditions as for thioethers [G02] LAH in the presence of copper salts or borohydrides in the presence of nickel salts (Figure 5.8). The deoxygenation of tertiary amine-oxides such as 5.16 and 5.17 can be performed with borohydride exchange resin-copper sulfate in methanol at room temperature or under reflux. This reaction tolerates other functional groups such as carbon-carbon double bonds, chlorides, epoxides, esters, amides, nitriles, sulfoxides, and sulfones [SA4] (Figure 5.8). 

Julia-Lythgoe olefination with, 34 reduction to thioethers, 115 reductive desulfurization, 70 synth. by oxn. of thioethers, 80, 216-217 Sulfonic adds catalysts for cationic reactions acetal hydrolysis, 337 acetafixations and transacetalizations,... 

Desulfurization (13, 158-159).1 In addition to desulfurization of thiols, thioethers, sulfoxides, and sulfones, Cp2Ni-LiAlHi (1 1) can serve as a hydrogenation catalyst for reduction of alkenes it also reduces enones to ketones, but in low yield. In general, it is similar in reactivity to Raney nickel and to (2,2 -bi-... 

An interesting feature is that the reductive desulfonylation can be carried out in the presence of thioethers and no desulfurization is observed (Eq. 69).125 This reagent also tolerates isolated and conjugated double bonds, ketones, acetals, and Boc carbamates. Sulfonamides, however, are not tolerated, and even at low reaction temperatures give the corresponding amines. 3-Elimination of arylsulfinates is also observed (Eq. 70).126... 

Autrey and Scullard used this fragmentation in a synthesis of corynantheine (11) from yohimban-l7-one (7). The synthesis also involved a novel desulfurization of the enol thioether (9) without reduction of the vinyl group. This step... 

Two syntheses of the trail pheromone, neocembrene (435), of Nasu-titermes spp. termites have been reported. Kodama et al. 185) (Scheme 78) prepared the allylic phenyl thioether (430) from trans,trans-gQX iny linalool (429). Terminal epoxidation of (430) followed by intromolecular cyclization, desulfurization, and dehydration led to (435). Kitahara et al. 186) cyclized fra 5-geranylgeranic acid chloride (436) with SnCU to afford chloroketone (437) (Scheme 79). Dehydrohalogenation of (437) and subsequent reduction of ketone (438) via acetate (441) gave neocembrene (435). 

Raney nickel is a highly active, finely divided form of the metal prepared by reaction of a nickel/aluminum alloy with concentrated sodium hydroxide, which removes most of the aluminum as Na[Al(OH)4], Although active for a very wide range of reductions, it has been particularly widely used for the reduction of nitriles, and the desulfurization of thioacetals, thioethers, and dithianes (see Section 19.3.3) (Figure 23.22). The careful disposal of the catalyst after use is very important once it has dried out, the metal is highly pyrophoric. 

Reduction. Raney Nickel desulfurization of 1,3-dithiolanes effects overall reduction of C=0 to CH2, as does Sodium-Ammonia in THF (eqs 4 and 5). Na/hydrazine is an alternative reagent (eq 6). Peptidic sulfoxides are reduced to thioethers with (1) and an electrophilic catalyst. ... 

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