D A Evans. D. Guterman Thermal Generation of carbene Intermediates Chem 206 Carbenes are Accessible via Sigmatropic Rearrangement The Automerization of Naphthalene(The Cume Question from Hell!) [1, 2] Shifts: Alpha-Alkynone Cyclizations H72 1 C-labeled Canh, at1035°c Conditions: 620C. 12-16 Torr, Quartz filled quartz Tube i Mechanism-1: L. T Scott, JACS 1977. 99, 4506 2s+2a S M 3 18 +2a 12s+r2a 1378% a For the azulene-naphthalene Isomerization: AG=-30.7 kcal/mol(298K The Activation energy for the isomerization: AG =+86 kcal/mol 89% I Mechanism-2, 3: L. T. Scot, JACS 1991, 113, 969 90% rpf, M tion -3 Karpf, M, Dreiding, A s, He/v. Chim. Acta. 67 1963(1984) A(HB-HA)=-34 kcal/mol (MNDO)D. A. Evans, D. Guterman Chem 206 Carbenes are Accessible via Sigmatropic Rearrangement O H O H H H O O O O O O O O O O O O O O Karpf, M., Dreiding, A.S., Helv. Chim. Acta. 67 1963 (1984) Clovene 80% (+ 19% isomers) 14 Torr N2 , 1 Hr 620° C Me Me O H H Me Me Me ■ [1,2] Shifts: Alpha-Alkynone Cyclizations Karpf, M., Dreiding, A., Helv. Chim. Acta. 65 13 (1982) Conditions: 620° C, 12-16 Torr, Quartz filled Quartz Tube [1,2] • • 90% 8 92 _ Recovery 54 46 _ 89% 78% 13 _ 87 80% 60 22 18 _ S.M. 3° 2° 1° The Automerization of Naphthalene (The Cume Question from Hell!) a– 13C-labeled C10H8 is isomerized into b– 13C-labeled C10H8 at 1035 °C D s 2s + s 2a p 2s + p 2a p 2s + p 2a s 2s + s 2a ■ For the azulene–naphthalene Isomerization: DG° = –30.7 kcal/mol (298K) ■ The Activation energy for the isomerization: DG ± = +86 kcal/mol H H ■ Mechanism-1: L. T. Scott, JACS 1977, 99, 4506; ■ Mechanism-2,3: L. T. Scott, JACS 1991, 113, 9692. H H •• H H H •• H H H •• H H H H X X B D(HB–HA) = –3.4 kcal/mol (MNDO) A BF BF B + A 900 °C 21%+ 79% Rationalize Thermal Generation of Carbene Intermediates Option–2 Option–3 O C-H insertion H D