Scheme 15. An overview of the skeletal transformations applied by Schreiber in the preparation of >4000 skeletally diverse small molecules. Reagents and conditions: (1) amine, LiClO₄ (or thiol); (2) alkylation, acylation or oxazolidone formation [for X = NR²]; (3) R³COC≡CH, Et₂AlCl; (4) heat.