Photoinduced Reactions of Metal Carbenes in Organic Synthesis

Abstract

The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cycloaddition reactions presented include reaction with imines to form b-lactams, with alkenes to form cyclobutanones, with aldehydes to form b-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations.

Carbene Radicals in Cobalt(II)–Porphyrin‐Catalysed Carbene Carbonylation Reactions; A Catalytic Approach to Ketenes

“…[1, 4, 5] The synthesis of medicinally important β-lactams by [2+2] ketene–imine cycloaddition reactions is especially important in this perspective. [5] Carbonylation reactions of Fischer carbene complexes have indeed been applied successfully to synthesise β-lactams. [5a, b] However, these are stoichiometric transformations, which hamper efficiency.…”

“…[5] Carbonylation reactions of Fischer carbene complexes have indeed been applied successfully to synthesise β-lactams. [5a, b] However, these are stoichiometric transformations, which hamper efficiency. Following the discovery of stoichiometric carbonylation reactions of Fischer-type carbene complexes, thus far only a few transition-metal-catalysed processes have been developed.…”

“…Following the discovery of stoichiometric carbonylation reactions of Fischer-type carbene complexes, thus far only a few transition-metal-catalysed processes have been developed. [5, 6] While interesting results have recently been obtained with a noble (palladium) metal catalyst, [5c] carbene carbonylation by base-metal catalysts reported thus far were associated with low efficiencies and required quite harsh reaction conditions (elevated temperatures and high CO pressures). [6] Therefore, we focused on the development of new catalytic carbene carbonylation processes by catalysts based on abundant first-row transition metals that operate under comparably mild reaction conditions.…”

“…Since ketenes are highly reactive [5, 6] and can generally only be trapped in the presence of a strong nucleophile, we first evaluated the activity of [Co II ( P1 )] ( P1 = tetraphenylporphyrin; Figure 1) in the catalytic carbonylation of ethyl diazoacetate (EDA; 1 ) in presence of aniline ( 2a ) under 10 bar CO at 50 °C. Under these conditions, (ethoxycarbonyl) ketene was formed and trapped by aniline to produce ethyl 2-(phenylcarbamoyl)acetate ( 3a ) in 57% isolated yield (Table 1, entry 1).…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…as Cr(CO) 5 CR 1 (R 2 ), leads to products consistent with the reactivity expected from ketenes [218][219][220]. For example, the carbenes readily react with imines after visible photoexcitation to form β-lactams, the four-membered ring common to all penicillin antibiotics, as shown in Figure 6.1.…”