2,3-Diaza-1,3-dienes (azines) as substrates for the Staudinger reaction. Synthesis and reactivity of N-imino-β-lactams

Article abstract of DOI:10.1021/jo00105a014

The reaction of aromatic and aliphatic azines with different ketene precursors, such as the acid chloride/Et₃N system, alkoxychromium(0) carbenes, and free diphenyl ketene, gives N-imino-β-lactams in good to excellent yields, with good levels of cis,trans-selectivity. A wide variety of symmetrically-substituted azines derived from aldehydes and ketones are compatible with the Staudinger reaction. Chiral N-imino-β-lactams derived from symmetrically or unsymmetrically (mixed) chiral azines are also obtained in good yields as essentially single enantiomers (de > 95%). Different reaction intermediates, including hemiaminals, oxadiazols, and hydrazides have been isolated. Free diphenyl ketene forms Diels-Alder adducts and N-acylazadienes in addition to the previously reported N-imino-β-lactams. The usual reactivity of the β-lactam ring is modified in N-imino-β-lactams by the presence of the imino group. Thus, β-hydrazonoesters, N-alkylamino-β-lactams, and NH-β-lactams can be efficiently obtained by base-catalyzed 2-azetidinone ring opening, catalytic hydrogenation, and ozonolysis, respectively.