Asymmetric Synthesis of Dihydrofurans via Rh(II)-Catalyzed Cyclopropanation-Rearrangement of Enol Ethers with 1-(Silanyloxy)vinyl Diazoacetates

Abstract

The cyclopropanation of dihydrofuran and dihydropy­ran with methyl 1-(silanyloxy)vinyl diazoacetates in the presence of chiral Rh(II)-catalysts affords cyclopropanes with high diastereo- and enantioselectivitiy. The cyclopropanes, in turn, rearrange to ­dihydrofurans upon desilylation with TBAF.

carbenes - catalysis - diazo compounds - transition ­metals - stereoselectivity

References

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10

Data of Methyl (1 R ^* ,5 S ^* ,6 S ^* )-6-{1-[( tert -Butyldi-methyl)silanyloxy]vinyl}-2-oxabicyclo[3.1.0]hexane-6-carboxylate ( 5a). [α]_D ¹⁸ -19 (c 1.12, EtOH, for 64% ee). IR (film): 2952 (w), 2855 (w), 1715 (s), 1632 (m), 1251 (s). ¹H NMR (500 MHz, CDCl₃): δ = 0.21 (d, J = 1.6 Hz, 6 H), 0.92 (s, 9 H), 2.14-2.19 (m, 1 H), 2.22-2.30 (m, 1 H), 2.41 (t, J = 6.0 Hz, 1 H), 3.65 (s, 3 H), 3.80 (dd, J = 8.5, 17.5 Hz, 1 H), 4.09 (ddd, J = 8.5, 10.1, 17.5 Hz, 1 H), 4.23 (d, J = 5.7 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = -5.3 (q), -4.7 (q), 18.0 (s), 25.5 (q), 26.0 (t), 32.4 (d), 39.5 (s), 51.9 (q), 70.7 (d), 71.8 (t), 96.0 (t), 150.5 (s), 171.2 (s). MS: m/z (%) = 298 (7)[M⁺], 242 (23), 241 (100), 209 (12), 166 (12), 89 (58), 75 (36), 73 (78), 59 (30). HRMS: m/z calcd for C₁₅H₂₆O₄Si⁺: 298.1601; found: 298.1642.

11

Data of Methyl (1 R ^* ,5 S ^* ,6 S ^* )-6-{1-[Tri(isopropyl)silanyl-oxy]vinyl}-2-oxabicyclo[3.1.0]hexane-6-carboxylate ( 5b).
[α]_D ²⁰ -8 (c 1.09, CHCl₃, for 82% ee). IR (film): 2946 (m), 2895 (w), 2867 (m), 1716 (s), 1631 (m), 1464 (m), 1331 (s), 1256 (s), 1181 (m), 1133 (m), 1113 (w). ¹H NMR (500 MHz, CDCl₃): δ = 1.10 (d, J = 7.3 Hz, 9 H), 1.11 (d, J = 7.4 Hz, 9 H), 1.25 (sept, J = 7.4 Hz, 3 H), 2.18-2.31 (m, 2 H), 2.43 (br t, J = 5.8 Hz, 1 H), 3.64 (s, 3 H), 3.85 (dd, J = 8.4, 17.1 Hz, 1 H), 4.10 (ddd, J = 8.4, 10.3, 17.1 Hz, 1 H), 4.22 (d, J = 5.7 Hz, 1 H), 4.36 (d, J = 1.0 Hz, 1 H), 4.39 (d, J = 1.0 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 12.7 (d), 17.9 (q), 18.0 (q), 26.0 (t), 32.4 (d), 39.8 (s), 51.8 (s), 70.8 (d), 71.9 (t), 95.3 (t), 150.6 (s), 171.3 (s). MS: m/z (%) = 340 (4)[M⁺], 297 (100), 117 (14), 115 (12), 89 (21), 87 (13), 77 (10), 75 (34), 73 (18), 61 (13), 59 (38). HRMS: m/z calcd for C₁₈H₃₂O₄Si⁺: 340.2070; found: 340.2062.

12 Davies HML. Churchill MR. J. Org. Chem.  1998,  63:  6586 

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14

Data of Methyl cis -2-Methyl-3a,4,5,6a-tetrahydro-furo[2,3- b ]furan-3-carboxylate ( 3).
[α]_D ¹⁸ +147 (c 1.12, EtOH, for 64% ee); [α]_D ¹⁸ +223 (c 1.13, for 84% ee). IR (film): 2952 (w), 1653 (s), 1641 (s), 1230 (s), 1080 (s). ¹H NMR (300 MHz, CDCl₃): δ = 2.06-2.13 (m, 2 H), 2.26 (d, J = 1.4 Hz, 3 H), 3.67-3.76 (m, 1 H), 3.76 (s, 3 H), 4.05-4.11 (m, 1 H), 6.12 (d, J = 6.2 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 14.2 (q), 31.7 (t), 47.0 (d), 50.9 (d), 67.1 (t), 103.4 (s), 109.7 (d), 165.9 (s). MS: m/z (%) = 184 (31)[M⁺], 153 (30), 152 (100), 125 (14), 124 (16), 110 (41), 109(16), 96 (17), 95 (15), 82 (29), 81 (14), 53 (18). HRMS: m/z calcd for C₉H₁₂O₄ ⁺: 184.0736; found: 184.0731. Enantiomer separation: GC (β-Dex, isothermal, 120 °C, τ₁ = 20.1 min, τ₂ = 22.0 min or β-Dex, isothermal, 130 °C, τ₁ = 12.6 min, τ₂ = 13.7 min). For data of ethyl ester corresponding to 3, see ref. [15]

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16

Data of Methyl (1 R ^* ,6 S ^* ,7 S ^* )-7-{1-[Tri(isopropyl)silanyl-oxy]vinyl}-2-oxabicyclo[4.1.0]heptane-7-carboxylate ( 9). Colorless oil. [α]_D ²⁰ -22 (c 1.07, CHCl₃, for 84% ee), [α]_D ²⁰ -32 (c 0.56, Et₂O, for 95% ee). IR (film): 2945 (m), 2866 (m), 1717 (s), 1633 (m), 1464 (m), 1390 (w), 1335 (m), 1282 (w), 1254 (s), 1237 (s), 1219 (m), 1204 (m), 1159 (m), 1133 (m), 1076 (s), 1042 (m), 1020 (s), 912 (w), 881 (m), 745 (s), 680 (s). ¹H NMR (500 MHz, CDCl₃): δ = 0.95-1.09 (m, 1 H), 1.22 (d, J = 6.6 Hz, 9 H), 1.23 (d, J = 6.6 Hz, 9 H), 1.24-1.31 (m, 3 H), 1.59-1.73 (m, 2 H), 1.96-1.99 (m, 1 H), 2.02-2.06 (m, 1 H), 3.11-3.17 (m, 1 H), 3.41 (s, 3 H), 3.51-3.56 (m, 1 H), 4.15 (d, J = 7.4 Hz, 1 H), 4.56 (d, J = 0.7 Hz, 1 H), 4.64 (d, J = 0.7 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 13.1 (d), 17.1 (t), 18.2 (q), 18.3 (q), 22.1 (t), 24.9 (d), 36.8 (s), 51.4 (q), 62.2 (d), 64.3 (t), 96.5 (d), 151.6 (s), 172.4 (s). MS: m/z (%) = 354 (2)[M⁺], 312 (23), 311 (100), 117 (10), 89 (15), 75 (23), 73 (10), 59 (26). HRMS: m/z calcd for C₁₉H₃₄O₄Si⁺: 354.2226; found: 354.2181.

17

Data of Methyl cis -6-Tri(isopropyl)silanyloxy-2,3,4,4a,7,7a-hexahydrocyclopenta[ b ]pyran-5-carboxylate ( 10).
IR (film): 2944 (m), 2866 (m), 1716 (w), 1693 (s), 1614 (s), 1463 (w), 1437 (m), 1383 (s), 1287 (w), 1233 (s), 1212 (s), 1188 (m), 1141 (m), 1105 (m), 1082 (s), 1050 (m), 1009 (w), 996 (w), 881 (s), 843 (w), 807 (s), 781 (s), 682 (s). ¹H NMR (500 MHz, CDCl₃): δ = 1.10 (d, J = 7.3 Hz,¹ 9 H), 1.11 (d, J = 7.5 Hz, 9 H), 1.17-1.25 (m, 3 H), 1.39-1.47 (m, 1 H), 1.54-1.62 (m, 1 H), 1.86-1.98 (m, 2 H), 2.53 (dd, J = 0.6, 5.5 Hz, 2 H), 2.85 (dd, J =12.1, 6.0 Hz, 1 H), 3.49-3.54 (m, 1 H), 3.66-3.73 (m, 1 H), 3.69 (s, 3 H), 4.15 (dd, J = 11.0, 5.5 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 12.9 (d), 17.7 (q), 17.8 (q), 22.2 (t), 24.0 (t), 40.4 (d), 40.6 (t), 50.4 (q), 64.4 (t), 72.9 (d), 109.4 (s), 163.9 (s), 165.5 (s). MS: m/z (%) = 354 (1)[M⁺], 312 (22), 311 (100), 89 (10), 75 (14), 59 (18). HRMS: m/z calcd for C₁₉H₃₄O₄Si⁺:354.2226; found: 354.2255.

18 Claridge TD. In High Resolution NMR Techniques in Organic Chemistry   Vol. 19:  Tetrahedron Organic Chemistry Series, Pergamon; Amsterdam: 1999. 

19 Fresenium W. Huber JFK. Pungor E. Rechnitz GA. Simon W. West TS. In Tables of Spectral Data for Structure Determination of Organic Compounds   2nd ed.:  Springer; Berlin: 1989. 

20

Crystal data for (C₂₅H₃₆N₂O₈Si), rac-13: M = 520.7, triclinic, P, a = 10.0195 (7), b = 13.3063 (8), c = 21.6204 (14)Å, α = 81.287 (7), β = 85.175 (8), γ = 75.576 (7)°, U = 2756.2 (3)ų, T = 200 K, Z = 4, µ (MoK_α) = 0.133 mm^-1 . The final R(F) = 0.047, wR(F)= 0.043 and S = 1.05. Both molecules of the asymmetric unit show similar conformations. CCDC-258850.

21

Data of Methyl cis -2-Methyl-3 a ,5,6,7 a -tetrahydro-4 H -furo[2,3- b ]pyran-3-carboxylate ( 11).
[α]_D ¹⁸ +144 (c 1.06, CHCl₃, for 95% ee). IR (film): 2950 (w), 1693 (s), 1633 (w), 1436 (m), 1381 (m), 1359 (w), 1333 (m), 1311 (w), 1259 (m), 1222 (w), 1187 (m), 1163 (m), 1139 (m), 1117 (m), 1085 (s), 1041 (w), 993 (m), 922 (m), 893 (m), 852 (s). ¹H NMR (400 MHz, CDCl₃): δ = 1.56-1.67 (m, 3 H), 1.92-1.98 (m, 1 H), 2.23 (d, J = 1.4 Hz, 3 H), 2.96-3.01 (m, 1 H), 3.70 (s, 3 H), 3.74-3.81 (m, 2 H), 5.77 (d, J = 7.6 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 14.3 (q), 19.8 (t), 22.1 (t), 37.9 (d), 50.8 (q), 60.8 (t), 104.1 (d), 106.7 (s), 166.2 (s), 167.7 (s). MS: m/z (%) = 198 (18)[M⁺], 167 (20), 166 (100), 139 (10), 138 (15), 124 (45), 110 (14), 96 (16), 95 (16), 82 (13), 67 (11). HRMS: m/z calcd for C₁₀H₁₄O₄ ⁺: 198.0892; found: 198.0903. Enantiomer separation: GC (β-Dex, isothermal, 130 °C, τ₁ = 19.0 min, τ₂ = 19.7 min). For data of ethyl ester corresponding to 11 see ref. 1, 15, 22.

22 Kraus GA. Johnston BE. Applegate JM. J. Org. Chem.  1991,  56:  5688