Diversification reactions of γ-silyl allenyl esters: selective conversion to all-carbon quaternary centers and γ-allene dicarbinols

Allenoate Prenucleophiles: A Triply Diastereoselective Approach to β-Hydroxy Esters Containing All-Carbon α-Quaternary Centers

Allenyl esters activated by titanium(IV) underwent additions to a wide range of aldehydes in high regio- and diastereoselectivities leading to products containing an all-carbon quaternary center bearing an α-vinyl group that was installed with high selectivity for the Z-geometry. An aldol product was also converted to an indanone offering a new route to this important compound class. Product triple diastereoselectivity has been rationalized using a concerted transition-state model.

Synthesis of functionalized cyclopentenes through allenic ketone-based multicomponent reactions

A novel and efficient synthesis of diversely functionalized cyclopentene derivatives through the multicomponent reactions of 1,2-allenic ketones with 4-chloroacetoacetate and malononitrile/cyanoacetate under mild and metal-free conditions is presented. Mechanistically, the formation of title compounds involves a cascade process including nucleophilic substitution, Michael addition and intramolecular aldol type reaction. Interestingly, when 1-phenyl allenic ketones bearing electron-donating groups on the phenyl ring were reacted with 4-chloroacetoacetate and cyanoacetate, methylenecyclo-pentanes, the regioisomer of cyclopentenes, were formed with good selectivity and high efficiency.