Organocatalytic Asymmetric CS Bond Formation: Synthesis of α‐Methylene‐β‐mercapto Esters with Simple Alkyl Thiols

Abstract

A highly efficient organocatalytic enantioselective C À S bond formation reaction between simple alkyl thiols and Morita-Baylis-Hillman (MBH) carbonates is described. The optically active a-methylene b-mercapto esters could be obtained under mild reaction conditions with excellent enantioselectivities (up to 97% ee). The broad scope and simple operation make this methodology very practical.

Phosphine–Thiourea‐Organocatalyzed Asymmetric C−N and C−S Bond Formation Reactions

“…Some complementary experimentsw ere carriedo ut in the case of cyclohexyl thiol. As reportedb yZ hu and Cheng, [7] using MgSO 4 ,a sa na dditive, in 1,4-dioxanec ould accelerate the reaction rate of the allylic substitution with thiols. On the contrary,inour studies, enantiomeric excess decreased dramatically,w ithoute ffect on reactivity,w hen adding 20 mol %o f MgSO 4 was employed (Table 4, entries 18-20).…”

“…[7] It should be noted that all catalytic systems used fort he CÀSb ond formations tartedf rom modified MBH adducts are tertiarya mine-basedo rganocatalysts. [5][6][7] No example of ap hosphine-catalyzed allylic substitution of MBH acetate or carbonate adducts for CÀSbond formation has been reported so far.In continuation of our research on the design and synthesis of new chiral organocatalysts, we have recently reported the synthesis of new bifunctional chiral phosphine-thiourea organocatalysts A, B and C,d erived from l-proline ( Figure 1). We have also described their applications in the asymmetric[ 3 + +2] cyclization between ethyl-butan-2,3-dienoate and N-benzylidene-p-toluenesulfonamide.…”

“…[ DHQD] 2 PHAL was found to be the best catalysta nd the presence of MgSO 4 is essential for increasing the reactionr ate. [7] It should be noted that all catalytic systems used fort he CÀSb ond formations tartedf rom modified MBH adducts are tertiarya mine-basedo rganocatalysts. [5][6][7] No example of ap hosphine-catalyzed allylic substitution of MBH acetate or carbonate adducts for CÀSbond formation has been reported so far.…”

“…1,4-Dioxane did not give good results, in contrast to that reported in the literature (Table 1, entry 3). [7] However,w hen benzene was used as as olvent, the reactionl ed to the formation of product with as light increasei ne nantiomeric excess, albeit al ower yield was recorded (Table 1, entry 4). The best yield (92 %) and enantioselectivity (65 % ee)w ere obtained when the reaction was carried out in toluene at 25 8Cf or 1day (Table1,e ntry 5).…”

Asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with α-fluoro-β-keto esters

“…Lewis base-catalyzed asymmetric allylic alkylations (AAA) of Morita–Baylis–Hillman (MBH) adducts [5–6], such as acetates and carbonates, have become an attractive option to access various chiral C - [7–19], N - [20–25], O - [26–30], P - [31–33] and S -allylic [34] and spirocyclic compounds [35–37]. Several protocols have been established to introduce fluorine atoms in AAA of MBH adducts.…”