Asymmetric radical cyclization leading to β-lactams: Stereoselective synthesis of chiral key intermediates for carbapenem antibiotics PS-5 and thienamycin

Catalytic, asymmetric reactions of ketenes and ketene enolates

“…Commonly, the lactam ring is formed through either ketene–imine cyclizations (another ketene application pioneered by Staudinger)58 or ester enolate–imine condensations59 (the Gilman–Speeter reaction). However, other notable methods are sometimes employed, including photoinduced rearrangements60 and radical cyclizations 61. Despite all of these synthetic methods for obtaining achiral or racemic β-lactams, until the last decade asymmetric methodology has remained scarce, largely limited to chiral auxiliary based systems 62.…”

Stereoselective synthesis of 3,4-diaryl β-lactams

“…18,19 Other methods are sometimes reported for preparing the b-lactam nucleus, including the isocyanate-ketone cycloaddition, 20 the chromium carbene-imine reaction, 21 the hydroxamate cyclization 22 and the radical photocyclizations. 23, 24 Alper et al reported the stereoselective synthesis of b-lactams by the rhodium-or cobalt-catalyzed expansion of the aziridinic ring. [25][26][27][28][29] The palladium-catalyzed cyclocarbonylation of allyl phosphates in the presence of imines under strong CO pressure leads to the stereoselective synthesis of b-lactams.…”

Functionalised Oximes: Emergent Precursors for Carbon-, Nitrogen- and Oxygen-Centred Radicals

“…Note the rate constants ( k c ) for 4- exo -closure of the but-3-enyl 43 and ring opening ( k d ) of the cyclobutylmethyl radical 44 in Scheme 8. The 4-member azetidinone ring system has proved to be exceptional because β-lactams have been prepared by cyclisations of carbamoyl radicals [63,64,65], of amidoalkyl radicals [66,67,68,69,70] and of amidyl radicals [71]. This topic has been reviewed in the context of homolytic ring closures in general [72].…”