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

Abstract

While B(C(6)F(5))(3) forms the adducts (CH(2))(4)CO(2)B(C(6)F(5))(3)1 and (CHMeCO(2))(2)B(C(6)F(5))(3)7 with δ-valerolactone and lactide, the frustrated Lewis pairs derived from B(C(6)F(5))(3) and phosphine or N-bases react with lactone to effect ring opening affording zwitterionic species of the form L(CH(2))(4)CO(2)B(C(6)F(5))(3) (L = tBu(3)P 2, Cy(3)P 3, C(5)H(3)Me(3)N 4, PhNMe(2) 5, C(5)H(6)Me(4)NH 6) while reaction with rac-lactide results in ring contraction to give salts [LH][OCCHMeCO(2)(CMe)OB(C(6)F(5))(3)] (L = tBu(3)P 8, Cy(3)P 9, C(5)H(3)Me(2)N 10, C(5)H(6)Me(4)NH 11). The mechanistic implications of these reactions are discussed.

Frustrated Lewis Pair Chemistry: Development and Perspectives

“…[176] In the case of lactone, ring opening affording zwitterionic species of the form L(CH 2 ) 4 CO 2 B(C 6 F 5 ) 3 …”

Ring‐opening of Epoxides Mediated by Frustrated Lewis Pairs

“…wB97X-D/6-31G(d,p) calculations for the formation of 5a revealed some interesting differences compared to the formation of 2a (see the Supporting Information). First, the activation barrierf or ring-opening is increased (TS 2 : DG°= 20.4 kcal mol À1 (5a)v s. 16.1 kcal mol À1 (2a)), due to the reduced P-nucleophilicity of 4.S econd, product formation by cyclization of intermediate III and elimination of the second FLP moiety is in this case amuch more facile process (TS 3 : DG°= 5.1 kcal mol À1 (5a) vs. 16.3 kcal mol À1 (2a)), likelyd ue to the reduced electrophilic- Figure 4. Plot of natural logarithm of FLP (1)concentration versus time determined by 31 P{ 1 H} NMR spectroscopy for the reaction of 1 (1 equiv) with 2phenyloxirane (1 equiv).…”

“…Reactionof1 with propylene sulfide (left) and molecular structure of 6 (right;ellipsoids are setat5 0% probability,h ydrogen atoms are omitted for clarity). Selectedb ond lengths []and angles [8]f or 6:P1 ÀS1 2.0280(5), S1ÀB1 2.1117 (19), B1ÀC1 1.670(2),C1 ÀP1 1.7875 (16); P1-S1-B1 75.48(5), S1-B1-C1 95.45(10), B1-C1-P19 4.23(10), C1-P1-S1 94.83(6);S 1-P1-C1-B1 0.92 (11). m-C 6 H 5 ), 7.09 (t, 3 J H,H = 7.5 Hz, 2H; m-C 6 H 5 ), 7.02 (t, 3 J H,H = 7.2 Hz, 1H; p-C 6 H 5 ), 6.92 (t, 3…”

“…19), a = 9.7345(5) , b = 11.9393(6) , c = 17.1612(8) , V = 1994,53(17) 3 , Z = 4, 1 = 1.187 Mg m À3 , m(Cu Ka ) = 2.166 mm À1 , F(000) = 768, 2q max = 144.28,2 4944 reflections, of which 3918 were independent (R int = 0.026), 218 parameters, R1 = 0.023 (for 3892 I > 2s(I)), wR2 = 0.062 (all data), S = 1.07, largest diff. peak/hole = 0.211/ À0.284 e À3 ,i nversion twin, x = 0.489 (16). CCDC 1827770 (2a), 1827771 (2b), 1827772 (3a), 1827773 (5a), 1827774 (5c), and 1827775 (6)contain the supplementary crystallographic data for this paper.T hese data can be obtained free of charge from The Cambridge Crystallographic Data Centre.…”

“…[15] Analogous reactions of 1,4-dioxane or 1,4-thioxane with B(C 6 F 5 ) 3 and an appropriate Lewis base result in CÀOb ond cleavage and the formation of ring-opened products of type B or C,r espectively. [14b] FLPs derived from P-or N-based Lewis bases andB (C 6 F 5 ) 3 also induce ring-opening of d-valerolactone to give zwitterionic species D, while the analogous reactions with rac-lactide result in ring contraction to give salts of type E. [16] Phosphine/borane FLPs also promote CÀCb ond scission of the three-membered cyclopropanes yieldingt he phosphonium borates F (Figure 1). [17] Commonly,t hese ring-opening reactions occurv ia nucleophilic attack by ab ase on aL ewis acid-activated cyclic molecule.…”