A Photochemical Two-Step Formal [5+2] Cycloaddition: A Condensation/Ring-Expansion Approach to Substituted Azepanes.

Seven-membered nitrogen-containing heterocycles are considerably underrepresented in the literature compared to their five- and six-membered analogues. Herein, we report a relatively understudied photochemical rearrangement of N-vinylpyrrolidinones to azepin-4-ones in good yields. This transformation allows for the conversion of readily available pyrrolidinones and aldehydes to densely functionalized azepane derivatives in a facile two step procedure.

Stereoselective Synthesis of Dioxolanes and Oxazolidines via a Desymmetrization Acetalization/Michael Cascade.

The desymmetrization of p-quinols using a Brønsted acid catalyzed acetalization/Michael cascade was achieved in high yields and diastereoselectivities for aldehydes and imines. Use of a chiral Brønsted acid allowed for the synthesis of 1,3-dioxolane and 1,3-oxazolidine products in modest enantioselectivity.

An asymmetric synthesis of 1,2,4-trioxane anticancer agents via desymmetrization of peroxyquinols through a Brønsted acid catalysis cascade.

The desymmetrization of p-peroxyquinols using a Brønsted acid-catalyzed acetalization/oxa-Michael cascade was achieved in high yields and selectivities for a variety of aliphatic and aryl aldehydes. Mechanistic studies suggest that the reaction proceeds through a dynamic kinetic resolution of the peroxy hemiacetal intermediate. The resulting 1,2,4-trioxane products were derivatized and show potent cancer cell-growth inhibition.

Photochemical synthesis of 3-alkynals from 1-alkynoxy-9,10-anthraquinones.

Photolysis of 1-(3-alkynoxy)-9,10-anthraquinones in deoxygenated methanol leads to moderate yields (35-45%) of 3-alkynals along with the unexpected formation of diacetals. Reaction of these 3-alkynals with Grignard and Wittig reagents occurs nearly quantitatively without rearrangement to their 2,3-dienal isomers.