Ring openings of lactone and ring contractions of lactide by frustrated Lewis pairs

While B(C6F5)(3) forms the adducts (CH2)(4)CO2B(C6F5)(3) 1 and (CHMeCO2)(2)B(C6F5)(3) 7 with delta-valerolactone and lactide, the frustrated Lewis pairs derived from B(C6F5)(3) and phosphine or N-bases react with lactone to effect ring opening affording zwitterionic species of the form L(CH2)(4)CO2B(C6F5)(3) (L = tBu(3)P 2, Cy3P 3, C5H3Me3N 4, PhNMe2 5, C5H6Me4NH 6) while reaction with rac-lactide results in ring contraction to give salts [LH][OCCHMeCO2(CMe)OB(C6F5)(3)] (L = tBu(3)P 8, Cy3P 9, C5H3Me2N 10, C5H6Me4NH 11). The mechanistic implications of these reactions are discussed.