Stereoselective Synthesis of the Decahydroquinoline Alkaloid cis-

Chiral Spirophosphoric-Acid-Catalyzed Divergent Vinylogous Mannich and aza-Friedel-Crafts Reactions of 2-Methoxyfuran

The first enantioselective vinylogous Mannich reaction is developed using 2-methoxyfuran under chiral spirophosphoric acid catalysis. The strategy involves 4-isoxazoline derivatives as cyclic ketimine surrogates and provides γ-butenolide scaffolds (up to 97% ee and >20:1 dr). The mechanistic investigations suggest that an in situ generated water molecule plays a crucial role in delivering γ-butenolide, while the use of molecular sieves delivers aza-Friedel-Crafts products. The synthetic utility of γ-butenolide is shown toward obtaining piperidone skeleton via a lactone-lactam rearrangement.

Highly (E)-Selective Trisubstituted Alkene Synthesis by Low-Valent Titanium-Mediated Homolytic Cleavage of Alcohol C-O Bond

Ti-mediated homolytic C-O bond cleavage was useful for cascade radical-ionic reactions. Benzyl alcohols treated with TiCl₄(col) (col = 2,4,6-collidine) and Mn powder generated the corresponding benzyl radicals; in addition, their reaction with 2-carboxyallyl acetates and the subsequent elimination of the acetoxy group yielded α,β-unsaturated carbonyl compounds with exclusive (E)-stereoselectivity. The simplicity of the procedure and its wide substrate scope represent a solution to the drawbacks associated with the reactions.

A Low-Cost and Scalable Synthesis of a Cyclohexanone-Related Bifunctional Building Block

A practical route to 2-(2-(2-methyl-1,3-dioxolan-2-yl)ethyl)cyclohexan-1-one was developed, featuring the use of inexpensive starting materials/reagents and readily attainable reaction conditions. The overall transformation was achieved in 53% yield with one chromatographic purification via NaOH-mediated aldol condensation, ethylene glycol protection of the ketone group in the presence of HC(OEt)₃/concd HCl, saturation of the C=C bond and the benzene ring with Al-Ni alloy in aqueous KOH, and oxidation of the intermediate cyclohexanol with aqueous NaClO/TEMPO/KBr.