Efficient synthesis of a small molecule, nonpeptide inhibitor of LFA-1

A three-stage process for the synthesis of LFA-1 inhibitor 1 from amine 4 with an overall yield of 65% is described. The key stage involves a Ph(3)PCl(2)-induced dehydration/cyclization of urea 6 followed by a regioselective bromination to give 1H-imidazo[1,2-a]imidazol-2-one 9. Br/Mg exchange of 9 followed by addition to SO(2) in THF and subsequent oxidation produces a sulfonyl chloride which is directly reacted with L-alaninamide using K(2)CO(3) as base in aqueous DMF/THF to give 1 in a one-pot operation. The process was implemented for the production of 1 on a metric ton scale.