T-BuSH

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

By using 10 mol% of 51, MS4A, and t-BuSH, the desired product 52 was obtained in up to 98% ee in 80% yield. A complementary role by two metals (Ga and Li) in activating and positioning both of the substrates has been proposed. The MS4A (sodium aluminosilicate) accelerated the reaction however, the actual role of this additive was not clearly defined, although the possibilty that MS4A delivers Na ions was pointed out. Tomioka et al. reported the asymmetric Michael addition of an aromatic thiol to a,P-unsaturated esters in the presence of 8 mol% of 53 to provide 54 in up to 97% ee in 99% yield (Eq. 7.40) [47]. 

Koshakji, R.P., R.D. Harbison, and M.T. Bush. 1984. Studies on the metabolic fate of [14C]2,3,7,8-tetrachlo-rodibenzo-p-dioxin (TCDD) in the mouse. Toxicol. Appl. Pharmacol. 73 69-77. 

Table 9. Catalytic asymmetric ring openings of symmetrical epoxides with t-BuSH (90) catalyzed by (R)-GaLB with MS 4A.

Ar-Acrylamidohexanoyl -lactosylamine 51 was telomerized (AIBN, MeOH) in the presence of either tcrt-butylmercaptan or methyl mercapto-propionate to provide families of discrete telomers 52 and 53 separable by size-exclusion chromatography (Scheme 9) [74,75]. Using 5.5 equivalents of t-BuSH per monomer gave monoadduct (27%), dimer (14%), trimer (1%), and higher telomers 52 (45%) in 87% yield. When methyl mercaptopropionate was used (0.43 eq), monoadduct 54 (26%), dimer (22%), trimer (12%), tetramer (7%), and hi er telomers 53 (n > 5,31 %) were obtained. 

Garcia, A.D., Doan, N.B., Imura, T., Bush, T.G., Sofroniew, M.V. (2004). GFAP-expressing progenitors are the principal source of constitutive neurogenesis in adult mouse forebrain. Nat Neurosci, 1,1233-41. 

An /V-allylaminium cation radical undergoes an addition-cyclization reaction with vinyl ethers in the presence of t-BuSH to give 3-alkoxy-4-methylpyrrolidines 72 (Scheme 23) in fair to good yields (90TL1675). In addition to EVE, 2,3-dihydrofuran and 3,4-dihydro-(2//)pyran also undergo reactions to give bicycles 73 and 74, respectively, in reasonable yield. 

Trapping Reagent t-BuSH - BrCCIj CHI3(2 eq.) PhSSPh (2 eq.)... 

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