A new one-pot approach to synthesize densely substituted racemic and enantiopure pyrroles from beta-lactams has been developed. The approach relies on the regiocontrolled cyclization of beta-allenamine intermediates derived from the ring opening of 2-azetidinone-tethered allenols. In this approach four points of diversity are introduced, one of which is the position of the allene moiety on the beta-lactam ring.

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo-, regio-, and stereocontrolled metal-catalyzed oxycyclization reactions of β,γ- and γ,δ-allendiols, which were readily prepared from (R)-2,3-O-isopropylideneglyceraldehyde. The application of Pd(II), Pt(II), Au(III), or La(III) salts as the catalysts gives controlled access to differently sized oxacycles in enantiopure form. Usually, chemoselective cyclization reactions occurred exclusively by attack of the secondary hydroxy group (except for the oxybromination of phenyl β,γ-allenic diols 3b and 3d) to an allenic carbon atom. Regio- and stereocontrol issues are mainly influenced by the nature of the metal catalysts and substituents.

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