Fit-for-Purpose Synthesis of a KRASG12C Covalent Inhibitor, via a Diastereoselective Hayashi Arylation

An enabling, fit-for-purpose synthesis of stereochemically pure KRASG12C covalent inhibitor 1, a potential new treatment for cancer, is described. The synthetic route provided 1 in 13 steps from commercially available 2-fluoro-5-methylaniline (2), tert-butyl (S)-3-methylpiperazine-1-carboxylate (8) and (S)-(1-methylpyrrolidin-2-yl)methanol (10). A key transformation in this sequence was the diastereoselective 1,4-addition of an aryl boronate derived from 2 with rac-4-methylcyclohex-2-en-1-one (rac-4) in a Hayashi arylation that sets two relative stereocenters of the target molecule. This in turn inspired the development of an improved synthesis of (R)-4-methylcyclohex-2-en-1-one ((R)-4) via optimized methodology for the asymmetric monohydrogenation of 1,4-dienes, thus setting the stage for a fully asymmetric synthesis of inhibitor 1.