B. Connell Fischer carbenes Chem 206 Recurring Themes The Wall of co Res O OCH3 OCH CO)5Cr (cO5Cr一 rotation about heteroatom carbene bond is restricted by 14-25 kcal'mol 53 Cr NMR is consistent with strong (CO)5Cr is sterically very larg resonance contribution Hegedus and Dotz JACS, 1988, 8413 Kinetic Electrophilicity HOCH (CO)5CI H .Formation of tetrahedral intermediate is 109 faster than CH3o- addition to BnO,C( enascon Chem. Soc. Rev., 1997. 299 JACs,1998,8632 pKa Data Thermodynamic Acidity 3C C (CO)sCr= (CO)cCra O= pKa(THF)=8 pKa(H2O)=12.3 quivalent to p-cyanophenol Casey, JACS, 1974, 1230 05/0612/20994:22PM
B. Connell Fischer Carbenes Chem 206 Recurring Themes OCH3 R CO CO OC OC CO Cr The Wall of CO • (CO)5Cr is sterically very large Resonance (CO)5Cr OCH3 R (CO)5Cr OCH3 R •Rotation about heteroatom carbene bond is restricted by 14-25 kcal/mol • 53Cr NMR is consistent with strong resonance contribution Hegedus and Dotz JACS, 1988, 8413. Bernasconi Chem. Soc. Rev., 1997, 299. JACS, 1998, 8632. Kinetic Electrophilicity (CO)5Cr OCH3 CH3 (CO)5Cr OCH3 CH3 •Formation of tetrahedral intermediate is 109 faster than CH3O– addition to BnO2CCH3. OCH3 H HOCH3 pKa Data (CO)5Cr OCH3 CH3 (CO)5Cr N CH3 H3C CH3 O N CH3 H3C CH3 • pKa = 20.4 (DMSO) • pKa = 35 (DMSO) Thermodynamic Acidity • pKa(THF) = 8 • pKa(H2O) = 12.3 equivalent to p-cyanophenol Casey, JACS, 1974, 1230. 05/06 12/20/99 4:22 PM
B. Connell Fischer carbenes Chem 206 ivity to Acid OCH3 pyridine (CO)5C (CO)5.pyr reductive el ⊙ pyridinium (CO)5CI (CO CH2 See Hegedus, JACS, 1990, 6255 Meta/ Removal and Functionalization CH3Li, CICH2l Barluenga, TL, 1994, 9471 80-90% CH2N2 OCH- Casey,TL,1973,1421 Ph3 PCH2 Casey, JACS, 1972, 65 (CO) Via similar intermediates OCH3 (CO)5Cr-y-Ar (CO)5Cl 070812/20/994:22PM
B. Connell Fischer Carbenes Chem 206 (CO)5Cr OCH3 CH3 pyridine H3CO + (CO)5Cr•pyr Sensitivity to Acid (CO)5Cr OCH3 CH2 (CO)5Cr OCH3 CH2 pyridinium pyridine H reductive elimination See Hegedus, JACS, 1990, 6255. (CO)5Cr OCH3 Ar CH3Li, ClCH2I O Ar CH3 80-90% Metal Removal and Functionalization Barluenga, TL, 1994, 9471. (CO)5Cr OCH3 R CH2N2 R OCH3 (CO)5Cr OCH3 Ar Ph3PCH2 H2C OCH3 Ar Casey, TL, 1973, 1421. Casey, JACS, 1972, 6543. Via similar intermediates: (CO)5Cr OCH3 Ar Cl (CO)5Cr OCH3 R N2 (CO)5Cr OCH3 Ar Ph3P 07/08 12/20/99 4:22 PM
Connell Fischer carbenes Chem 206 Selected Reactions of Unsaturated Fischer Carbene Complexes (CO)5CI (CO)5CI Nu H CH3 R2 R3 OCH3 OCH3 Selected Reactions of saturated Fischer Carbene Complexes H3 R6 (CO)5M RI OCHR R3 HR2R3 RCHO (CO)5M CH3 OCH3 XR6=OCH3, N(R5)2 R3 SnCI R2 091012/20993:51PM
B. Connell Fischer Carbenes Chem 206 (CO)5M OCH3 R3 R2 R1 R1 R3 R2 (CO)5Cr OCH3 R4 R4 Nu (CO)5Cr OCH3 R3 R2 R1 Nu R R2 = H OH OCH3 R1 R3 R R R2, R3 ≠ H O OCH3 R1 R3 R R2 R4 R1 R2 R4 OCH3 R3 Bu3SnH Bu3Sn OCH3 R3 R2 R1 R R2 = NR2 O R R OCH3 R3 N H3CO R4 R5 R2 R3 HN R4 R5 Selected Reactions of Unsaturated Fischer Carbene Complexes Selected Reactions of Saturated Fischer Carbene Complexes (CO)5M XR6 CH3 XR6 = OCH3, N(R5)2 (CO)5M XR6 R OH RCHO CH3 OCH3 R1 R1 O R1 OCH3 CH3 O O H3C R2 R3 OCHR2R3 OCHR2R3 R O O OCH3 CH3 R O N R2 R1 N R O 2 R1 CH3 XR6 R3SnCl R3Sn XR6 RX (CO)5M XR6 R R O (CO)5M XR6 O R 09/10 12/20/99 3:51 PM
B. Connell Fischer carbenes Chem 206 n-Bu (CO)5Mo THF,65°C 78% OCH Harvey, TL, 1990, 2529 OCH Wulff Chem,1988,137 OCH OCH 81% Harvey, JACS, 1992, 8424 (CO)5Cr Hoye, JACS, 1988, 2676 11/1212/20993:54PM
B. Connell Fischer Carbenes Chem 206 Cyclopropanation OCH3 (CO)5Mo n-Bu CO2CH3 THF, 65 °C 78% CO2CH3 n-Bu OCH3 E:Z 1.9:1 Harvey, TL, 1990, 2529. OCH3 (CO)5Mo CH3 OTBS 25 °C, 49% TBSO OCH3 CH3 >95% cis Wulff Pure Appl. Chem., 1988, 137. JACS, 1988, 2653. Cyclopropanation R OCH3 1 (CO)5Cr R2 M(CO)4 R2 OCH3 Reaction with Alkynes R1 M(CO)4 R2 OCH3 (CO)5Cr OCH3 PhH reflux 97% OCH3 Hoye, JACS, 1988, 2676. O OCH3 (CO)5Cr n-Bu PhH, 100 °C 81% O OCH3 n-Bu Harvey, JACS, 1992, 8424. R1 11/12 12/20/99 3:54 PM
B. Connell Fischer carbenes Chem 206 Selective Cyclopropanation Ph,OCH3 THF,80°C,3h t-B (CO)5Cr n-Bu △NcH n-Bu, DMF,152°C.4%BHT 30 min 88%,97%de mun,1995,665 997,7591 Cyclopropanation Reaction with Alkynes Phh CO2Et CO2E Harvey, JOC, 1992, 5559 13/1412/20993:55PM
B. Connell Fischer Carbenes Chem 206 Selective Cyclopropanation Barluenga Chem. Commun., 1995, 665. JACS, 1997, 7591. n-Bu Fe (CO)5Cr OCH3 88%, 97% de Fe OCH3 H n-Bu DMF, 152 °C, 4% BHT 30 min N Ph H t-Bu OCH3 (CO)5Cr Ph THF, 80 °C, 3 h Ph OCH3 Ph H H N t-Bu SiO2 Ph OCH3 Ph H H O H H O OCH3 H n-Bu H O3 Cyclopropanation Reaction with Alkynes Harvey, JOC, 1992, 5559. O CH3 Mo(CO)5 O CO2Et PhH 65 °C, 55% O CH3 O H CO2Et O O CH3 CO2Et H 13/14 12/20/99 3:55 PM