Rhodium-Catalyzed Alkene Difunctionalization with Nitrenes.

The Rh(II) -catalyzed oxyamination and diamination of alkenes generate 1,2-amino alcohols and 1,2-diamines, respectively, in good to excellent yields and with complete regiocontrol. In the case of diamination, the intramolecular reaction provides an efficient method for the preparation of pyrrolidines, and the intermolecular reaction produces vicinal amines with orthogonal protecting groups. These alkene difunctionalizations proceed by aziridination followed by nucleophilic ring opening induced by an Rh-bound nitrene generated in situ, details of which were uncovered by both experimental and theoretical studies.

Catalytic intermolecular alkene oxyamination with nitrenes.

The Rh(II)-catalyzed intermolecular addition of nitrenes to aromatic and aliphatic alkenes provides vicinal amino alcohols with yields of up to 95 % and complete regioselectivity. This 1,2-oxyamination reaction involves the formation of an aziridine intermediate that undergoes in situ ring opening. The latter is induced by the Rh-bound nitrene that behaves as a Lewis acid.

Gold (III) Chloride-Catalyzed 6-- Oxa-Michael Addition Reactions for Diastereoselective Synthesis of Fused Tetrahydropyranones.

Alkynones were treated with boron trifluoride diethyl etherate to generate β-iodoallenolates, which underwent intramolecular aldol reactions to produce cycloalkenyl alcohols. Diastereoselective oxa-Michael ring closure could then be induced by treatment with a catalytic amount of gold(III) chloride, affording highly functionalized tetrahydropyran-containing ring systems.

Cascade cyclizations of acyclic and macrocyclic alkynones: studies toward the synthesis of phomactin A.

A study of the reactivity and diastereoselectivity of the Lewis acid promoted cascade cyclizations of both acyclic and macrocyclic alkynones is described. In these reactions, a β-iodoallenolate intermediate is generated via conjugate addition of iodide to an alkynone followed by an intramolecular aldol reaction with a tethered aldehyde to afford a cyclohexenyl alcohol. The Lewis acid magnesium iodide (MgI2) was found to promote irreversible ring closure, while cyclizations using BF3·OEt2 as promoter occurred reversibly.

A macrocyclic β-iodoallenolate intermediate is key: synthesis of the ABD core of phomactin A.

An enantioselective strategy for the synthesis of phomactin natural products is described. The Lewis acid triggered cyclization of a β-iodoallenolate embedded in a 12-membered macrocycle was used to obtain a highly functionalized bicyclo[9.3.

Experimental and theoretical studies on the Nazarov cyclization/Wagner-Meerwein rearrangement sequence.

Highly functionalized cyclopentenones can be generated by a chemoselective copper(II)-mediated Nazarov/Wagner-Meerwein rearrangement sequence of divinyl ketones. A detailed investigation of this sequence is described including a study of substrate scope and limitations. After the initial 4π electrocyclization, this reaction proceeds via two different sequential [1,2]-shifts, with selectivity that depends upon either migratory ability or the steric bulkiness of the substituents at C1 and C5.

Beta-iodoallenolates as springboards for annulation reactions.

Beta-iodoallenolates II, generated from alkynones I with tetra-n-butylammonium iodide and a Lewis acid, underwent selective single or double annulation, depending on the Lewis acid promoter. Treatment with TiCl(4) gave cyclohexenyl alcohols III, whereas BF(3) x OEt(2) gave oxadecalins IV. The scope and limitations of the two annulation reactions are described.