Tert-butyl thioacetate

C6H120S S-tert-butyl thioacetate 999-90-6 407.10 35.035 1,2 8540 C6H1203 ethyl 2-hydroxy-2-methylpropanoate 80-55-7 423.15 36.552 1,2... 

A related Mukaiyama aldol catalyst system reported by Keck prescribes the use of a complex that is prepared in toluene from (R)- or (S)-BINOL and Ti(0 Pr)4 in the presence of 4 A molecular sieves. In work preceding the aldol addition reaction, Keck had studied this remarkable catalyst system and subsequently developed it into a practical method for enantioselective aldehyde allylation [95a, 95b, 95c, 96]. Because the performance of the Ti(IV) complex as an aldol catalyst was quite distinct from its performance as a catalyst for aldehyde allylation, a careful examination of the reaction conditions was conducted. This meticulous study describing the use of (BINOL)Ti(OiPr)2 as a catalyst for aldol additions is noteworthy since an extensive investigation of reaction parameters, such as temperature, solvent, and catalyst loading and their effect on the enantiomeric excess of the product was documented. For example, when the reaction of benzal-dehyde and tert-butyl thioacetate-derived enol silane was conducted in dichlo-romethane (10 mol % catalyst, -10 °C) the product was isolated in 45% yield and 62% ee by contrast, the use of toluene as solvent under otherwise identical conditions furnished product of higher optical purity (89% ee), albeit in 54% yield. For the reaction in toluene, increasing the amount of catalyst from 10 to 20 mol %... 

To further exploit the potential usefiilness of this new family of clusters, monoadduct 54 was saponified into 55 (0.05 M NaOH, quant) and condensed to L-lysine methyl ester using 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline (EEDQ) to give extended dimer 56 in 50 % yield together with monoadduct in 15 % yield [75]. Additionally, tert-butyl thioethers 52 could be transformed into thiols by a two step process involving 2-nitrobenzenesulfenyl chloride (2-N02-PhSCl, HOAc, r.t, 3h, 84%) followed by disulfide reduction with 2-mercaptoethanol (60%). Curiously, attempts to directly obtain these thiolated telomers by reaction with thioacetic acid f ed. These telomers were slightly better ligands then lactose in inhibition of binding of peanut lectin to a polymeric lactoside [76]. 

Aggarwal and co-workers have used Jackson s metal peroxide oxidants for the epoxidation of ketene thioacetals. This resulted in highly diastereoselective epoxide formation (>20 1 selectivity).136 Carmen Carreiio and colleagues showed that epoxidation of (S)-(2-p-tolylsulfonyl)-2-cyclohexan-1 -ol and its OAc and OMOM derivatives, with lithium tert-butyl hydroperoxide, proceeds with high stereoselectivity to give the syn epoxy alcohols.137... 

Aldol additions to ethyl pyruvate 131 by silyl ketene thioacetals 132,133,134 have been shown to proceed in high yields and superb levels of induction (Eq. 13). This process represents an uncommon example of catalytic, asymmetric aldol additions to ketones, providing access to synthetically useful compounds such as 137. The remarkable ability of the catalyst to differentiate between subtle ster-ic differences of substituents flanking a 1,2-diketone was elegantly demonstrated in the highly enantioselective additions to 2,3-pentanedione 136 (Eq. 14). The aldol adduct of S-tert-butyl thiopropionate derived silyl ketene acetal afforded 2,3-a tz-aldol adduct (>99 1 anti/syn) in 98% ee and 97 3 chemoselectiv-ity for the methyl ketone [86]. 

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