Phosphine-thiourea based-organocatalysts derived from l-proline promoted CÀN or CÀS bond formation of tert-butoxycarbonyloxy-Morita-Baylis-Hillman adducts with phthalimide or alkyl thiols, respectively. Good yields and enantioselectivities up to 93 % were achieved.Over the past decade, asymmetric Morita-Baylis-Hillman (MBH) and aza-MBH reactions have been studied intensively by many research groups owing to their advantages such as atom economy, non-metal catalyst, mild conditions, and especially ease of access to functionalized and complex molecules.[1] The transformations of MBH adducts have attracted considerable interest of organic chemists who focused on the development of new organocatalytic procedures, [2,3] in particular the allylic substitution.[3] The conversion of the allylic hydroxyl group of the MBH adduct into a better leaving group such as an acetate (OAc) or a tert-butoxycarbonyloxy (OBoc) group creates an electrophilic character at the allylic position of the MBH adduct. However, due to the steric hindrance at the allylic position, the nucleophilic substitution of MBH adducts proceeds through successive S N 2'-S N 2' reactions in the presence of a Lewis base (LB) catalyst (Scheme 1). [4] Chiral phosphine or amine-catalyzed asymmetric allylic substitution reactions have been powerful and versatile tools for the CÀC, CÀN, CÀO, and CÀP bond construction.[4] However, if several organocatalytic procedures exist for the CÀS bond formation, [5] examples including the allylic substitution of modified MBH adducts are very scarce.[6] To our knowledge, only one example of an asymmetric allylic substitution of alkyl thiols with MBH carbonate adducts catalyzed by a chiral amine has been reported. Indeed, Cheng and Zhu described the synthesis of a-methylene-b-mercapto esters in good yields and with excellent enantioselectivities.[DHQD] 2 PHAL was found to be the best catalyst and the presence of MgSO 4 is essential for increasing the reaction rate. [7] It should be noted that all catalytic systems used for the CÀS bond formation started from modified MBH adducts are tertiary amine-based organocatalysts. [5][6][7] No example of a phosphine-catalyzed allylic substitution of MBH acetate or carbonate adducts for CÀS bond 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, derived 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.[8] Herein, we report the use of these phosphine-thioureas in the asymmetric allylic substitu-

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