Synthesis of .beta.-Lactones by the Photochemical Reactions of Chromium Alkoxycarbene Complexes with Aldehydes

The Noncarbonylative Photochemistry of Group 6 Fischer Carbene Complexes

“…The noncarbonylative photochemistry of group 6 metal carbene complexes presented above clearly shows a strong dependence of the nature of the reaction products on the substituent on the nitrogen atom bonded to the carbene carbon atom 12,13. This fact clearly differentiates these photochemical reactions from the photocarbonylation pathway2,3,5 that either leads to ketene‐derived products or unreacted starting materials. Complexes 1 and tungsten(0)–carbene complexes 3a lead to syn‐N ‐metalated imine compounds 2 and 4 through 1,2‐dyotropic processes.…”

“…The irradiation of group 6 (Fischer) metal carbene complexes with visible light in the presence of nucleophiles leads to the formation of β‐lactams,1 cyclobutanones,2 amino acids and peptides,3 polynuclear hydrocarbons,4 and β‐lactones (Scheme ) 5. This rich and synthetically powerful photoreactivity6 has no parallel in the photochemistry of any other class of organometallic compounds.…”

Organometallic photochemistry at the end of its first century

“…For example, reactions with immines yield b-lactams [117], aldehydes yield lactones [118], alkenes yield cyclobutanones [119], and alcohols and amines yield substituted acids and amides, respectively [120]. These reactions have been extensively reviewed [121].…”

Formation of a Four‐Membered Ring

“…Under these reaction conditions (CO pressure), chromium can be recovered in up to 90% yield as chromium hexacarbonyl when the reaction solution is triturated with methanol (in which chromium hexacarbonyl is insoluble). A number of cyclization reactions have also been performed; upon irradiation of the aldehyde 97 an intramolecular addition of the carbonyl function to the intermediately generated ketene takes place, such that the bicyclic lactone 98 was isolated in good yield (reaction 40) [95]. A seven-membered ring was formed during this transformation.…”