Optically active quaternary carbon centers from the photoaddition of chromium-alkoxycarbene complexes and optically active thiazolines

Abstract

desilylating agents gave mixtures of products of transannular cyclization (and protodesilylation) which, being all known compounds, could be identified and determined by quantitative 13C NMR without separation. At lower temperatures (Table II, runs 6-9) a new product was formed, 11, which was isolated from run 7 by chromatography (silica gel, ether) as the first eluted material; cryst hexane-benzene (80 mg, 33%), mp 110-111 °C. 13C NMR:

Construction of Quaternary Stereogenic Centers via [2 + 2] Cycloaddition Reactions. Synthesis of Homochiral 4,4-Disubstituted 2-Azetidinones and Imine Substituent Effects on β-Lactam Formation

“…Prior to the present study, no efficient strategies either for the creation of quaternary centers at the C(4) position of the β-lactam ring or for controlling the stereochemistry at the newly created stereogenic centers have been described in the literature . In a pioneering approach, Slusarchyk and Godfrey applied the well established hydroxamate methodology 13c to the formation of C(4) disubstituted β-lactams, but the method was overshadowed by rearrangement processes.…”

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

“…Benzyl 2-Hydroxyhexanoate (15) and 1, 1 ‘ - [Pentylidenebis(oxymethylene)]bis(benzene) (16). A solution of tetramethylammonium pentacarbonyl(1-oxopentyl)chromate(1−) ( 3 ) (351 mg, 1.00 mmol) and benzenemethanol (0.21 mL, 2.00 mmol) in Et 2 O (20 mL) was reacted with HCl (5.0 mL, 5.00 mmol, 1 M in Et 2 O) and CO as described above. Irradiation (20 h), extraction, and chromatography using, in sequence, hexanes−EtOAc (1:1) and hexanes−EtOAc (3:7) gave, in order of elution, 16 (59 mg, 0.21 mmol, 21%) and 15 (30 mg, 0.14 mmol, 14%) as colorless liquids.…”

Synthesis of Three‐Membered and Four‐Membered Heterocycles with the Assistance of Photochemical Reactions

“…The photochemical reaction of Fischer carbine complexes and olefins or imines was performed for efficient preparation of cyclobutanones and β-lactams [103][104][105][106][107][108][109][110][111][112][113][114][115][116][117], respectively, in high yields (Scheme 31). The topological indicator [2 + 1 + 1] connects the olefin cadmium-carbon or imine cadmium-nitrogen, two-atom fragments, one carbon monoxide, and the carbene carbon.…”