No abstract

Assignments of relative configuration of the newly formed stereogenic center at the bridgehead carbon atom of bicyclic carbapenams obtained in Kinugasa reaction can be easily achieved by analyzing chemical shifts of the H-2 proton and geminal protons of the protected alkoxymethyl group at the C-2 carbon atom. The differences of 1 H NMR chemical shifts of these protons fall in two ranges of about 3.3-3.7 ppm, and 4.0-4.4 ppm. This observation can be attributed to the influence of the anisotropy of the neighboring carbonyl group and can be easily correlated with configuration at the bridgehead carbon atom.

The copper(I)-mediated reaction between five-membered cyclic nitrones and terminal acetylenes, leading to the assembly of the basic skeleton of carbapenem antibiotics is described. The diastereoselectivity of this cycloaddition-rearrangement cascade, a process known as the Kinugasa reaction, with respect to the structure and configuration of both substrates, as well as the reaction conditions, are discussed. Application of the described methodology to sugar-derived nitrones offers an attractive entry toward thienamycin and related compounds.