Photolytic Reaction of Hydroxy Fischer Carbene Complexes:  Synthesis of α-Hydroxy Esters

Abstract

Photolytic reaction of in situ generated pentacarbonyl(1-hydroxyalkylidene)chromium complexes in the presence of an alcohol, under 6 atm of carbon monoxide, affords R-hydroxysubstituted esters in low to moderate yield. Acetals, formed via thermal decomposition of the carbenes, are in some cases the major product.

Photoinduced Reactions of Metal Carbenes in Organic Synthesis

“…Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding "ate" complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals, presumably formed by thermal decomposition of the carbenes, were major by-products.…”

Photoinduced Coupling of CO and Vinylidene LigandsFormation of Cyclobutane-1,3-diones

“…The photolysis of heteroatom-stabilized carbene complexes of chromium and molybdenum (Fischer carbene complexes) in the presence of various substrates such as imines, olefins, aldehydes, amines, alcohols, CO, and isocyanides provides a convenient route to, for instance, β-lactams, imidazolines, azapenams, dioxocyclams, cyclobutanones, butenolides, β-lactones, 2-aminobutyrolactones, amino acid derivatives, α-hydroxy acid derivatives, and various other products . These reactions are assumed to be initiated by a photolytically induced coupling of a CO ligand with the carbene ligand to generate metal-coordinated ketenes.…”

Thermal Decomposition of Pentacarbonyl(1-acyloxyalkylidene)chromium(0) Complexes: Formation of Z-Enol Esters

“…( Z )-3-Phenyl-1-propen-1-yl Acetate (19). Reaction of tetramethylammonium pentacarbonyl(1-oxo-3-phenylpropyl)chromate(1−) ( 7 ) (798 mg, 2.00 mmol) with acetyl bromide (142 μL, 2.00 mmol) in CH 2 Cl 2 (40 mL) at −40 °C to ambient temperature (20 h), as described above, gave, after solvent removal at water aspirator pressure (0 °C) and chromatography (pentane−Et 2 O, 8:2), 19 (92 mg, 0.52 mmol, 26%, Z/E = 17:1) as a faint yellow oil …”