A study of the ring-opening of lactides and related cyclic esters by Ph2SnX2 and Ph3SnX compounds (X = NMe2, OR)

Ph3SnX reacts with L-lactide in the order X = NMe2 similar to OMe >> OPri > OBut in the initial ring-opening event. The rate of ring-opening of methyl substituted 1,4-dioxane-2,5-diones decreases with methyl substitution and ring-opening of 3,3,6,6-tetramethyl-1,4-dioxane-2,5-dione is not observed. From studies of the reaction between Ph3SnOPri and L-lactide the activation parameters DeltaH(not equal) 13(1) kcal mol(-1) and DeltaS(not equal) = -37(3) eu have been determined. Ph3SnNMe2 reacts with cyclic esters and propylene carbonate at low temperatures to give isolable ring-opened products. The compound Ph3Sn[OCHMeC(O)OCHMeC(O)X] ( where X = NMe2, OMe) are labile in solution at room temperature, yielding Ph3Sn[OCHMeC(O)X] and Ph3Sn[OCHMeC(O)](n)X, where n greater than or equal to 3, by transesterification, along with other minor products due to phenyl/OR group transfer (i.e., Ph4Sn). Ph2Sn(NMe2)(2) and L-lactide react to give Ph2Sn[OCHMeC(O)NMe2](2) by ring-opening of L-lactide followed by rapid amidation. A related compound, Ph2Sn[OCHMeC(O)OPri](2), is also formed in the reaction between Ph2Sn(OPri)(2) and L-lactide but is more labile toward further ring-opening of L-lactide.