Science of Synthesis

Koo, S., Science of Synthesis, (2010) 45, 1405.

Thermal or photochemical decomposition of ethyl diazoacetate in benzene produces transient (ethoxycarbonyl)carbene, which undergoes addition to benzene to give the unstable norcaradiene intermediate ‌195‌ that is in equilibrium with the more stable cycloheptatriene tautomer ‌196‌ (‌Scheme 43‌).[‌187‌] The kinetic nonconjugated isomer ‌196‌ undergoes thermally or photochemically induced sigmatropic rearrangement to three conjugated cycloheptatriene tautomers. The thermal or photochemical Buchner reactions are thus characterized by the formation of inseparable mixtures of cycloheptatrienyl esters. This problem can be solved by the use of an electron-poor rhodium(II) carboxylate catalyst at room temperature for the generation of (ethoxycarbonyl)carbene.[‌188‌] The kinetic product, ethyl cyclohepta-2,4,6-triene-1-carboxylate (‌196‌) can be obtained quantitatively with rhodi­um(II) trifluoroacetate in a large excess of benzene. The rhodium(II)-catalyzed decomposition of α-diazoamide ‌197‌ leads to a transient metal–carbenoid which may undergo two different intramolecular reactions: either addition to the aromatic ring to afford cycloheptapyrrolone ‌198‌ or insertion into the benzylic C—H bond to give β-lactam ‌199‌ (‌Scheme 43‌).[‌189‌] The chemoselectivity can be controlled by the ligand in the rhodium(II) catalyst. Thus, the perfluorobutanamide ligand favors attack on the aromatic ring to give cycloheptapyrrolone ‌198‌ in 70% yield together with some cis-β-lactam ‌199‌ (12% yield).

‌Meeeee 88‌ Meeeeee-Meeeeeeee Meeeeeee ee Meeee Meeeeeeee[‌888‌,‌888‌]

Mee eeeeeee(MM) eeeeeee eeeeeeeee eeeeeeeeeeeeee Meeeeee eeeeeeee ee eeeee eeeeeee ‌888‌ eeeeeeee eeee eeeeeeeee eeeeeeeeeeeeeeeeeeee ee eee eeeee-eeeeeeeeeee eeeeeeeeee, eeeee eeeee ee e eeeeeee eeeeeeeeeeeee eeeeeee ee eeeeeeeeeeee ‌888‌ eee eeeeeeeeeeeeeeee ‌888‌ (‌Meeeee 88‌).[‌888‌] Mee β-eeeee eeeeeeeeeee M8 ee eeeee eeeeeee ‌888‌ eeeeeeeeeee eee eeeeeeeeeee eeeeeeee eeeeeeeee ee eeeeeeeee eeeeee eeeeeeee ee eee eeeeeeeeeeeee eeee (M8 = M). 8M MMM eeeeeeeeeeeee eeeeeeee ee eeeeeeeeee eeeeeeeee eeee eee eeee ee eee eeeee-eeeeeeeeeee eeeeeee eee eeeeeeeeeeee eeeeeeee ‌888‌ ee eeeeeeeeeee ee eeeeeeeeeee ee eeee eeeeeeeeeee, eeeeeee eee eeeeeeee ee eee eeeeeeeeeee ee eee eeeee eee-eeeeeee eeee eeee eeeeee eee eeeeeeeeeeeeeeee ‌888‌.

‌Meeeee 88‌ Meeeeeeeeeeeeeeee ee eee Meeeeee-Meeeeeeee Meeeeeeeeeeeee Meeeeee Meeeeeee[‌888‌]

‌Meeeeeeeeee 88‌

e Meeeeeeeeeeeee eeeeee eeee eeeeeeeeee ee 8M MMM eeeeeeeeeeee ee eee eeeee eeeeeeee.

e Mee eeeeeee ee eee eeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeeeee eee eeee eeeeeeee ee 88% eeeee.

Meeeeeeeeeee Meeeeeeee

eeeee-(8M*,8eM*)-8e-Meeeee-8,8e-eeeeeee-8-eeeeeeeeeeee-8(8M)-eee (‌888‌/‌888‌, M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

8-Meeee-8-eeeeeeeeeee-8-eee (‌888‌, M8 = Me; 88 ee, 8.888 eeee) ee MM8Me8 (888 eM) eee eeeee eeeeeeee eeee 8 e ee e eeeeeeeee eeee ee Me8(MMe)8 (8.8 ee) ee MM8Me8 (888 eM), eeeee eeeeeeee eeeee M8. Mee eeeeeeee eee eeeeeeeee ee MMM eee eee eeeeeeee eeee eee eeeee eeeeee eee eeee eeeee. Meeeeee ee eee eeeeeee eeeee eeeeeee eeeeeeee eeee eee eeeee eeeeeee ee e eeeeee eee. M 8M MMM eeeeeeee ee eee eeeee eeeeeee eee eeeeeeee ee eeeeeeeee eee eeeeeeeeee ee eee eeeeeeeeeee eee eee eeeeeeeeeeeeee eeeee ee eee eeeeeeeeee eeeeee [eeeee-‌888‌/‌888‌ (δM8-M 8.88–8.88)/eee-‌888‌/‌888‌ (δM8-M 8.88–8.88) = 88:8]. Meeeeeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MeMMe/eeeeee eeeeeeee) eeee e eeeeee eeeeeeeeeeee ee eee eeeeeeeee; eeeee: 88 ee (88%).

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88e8, 8888.
• 8.Meeeee-Meee, (8888) M 88e8, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 888.