Synthesis of 1,4‐Cyclohexadiene Carboxylates through a Formal [2+4]‐Cycloaddition of Propiolates under Cobalt Catalysis

Chemodivergent, Regio- and Enantioselective Cycloaddition Reactions between 1,3-Dienes and Alkynes

Alkynes and 1,3-dienes are among the most readily available precursors for organic synthesis. We report two distinctly different, catalyst-dependent, modes of regio- and enantioselective cycloaddition reactions between these classes of compounds providing rapid access to highly functionalized 1,4-cyclohexadienes or cyclobutenes from the same precursors. Complexes of an earth abundant metal, cobalt, with several commercially available chiral bisphosphine ligands with narrow bite angles catalyze [4+2]-cycloadditions between a 1,3-diene and an alkyne giving a cyclohexa-1,4-diene in excellent chemo-, regio- and enantioselectivities. In sharp contrast, complex of a finely tuned phosphino-oxazoline ligand promotes unique [2+2]-cycloaddition between the alkyne and the terminal double bond of the diene giving a highly functionalized cyclobutene in excellent regio- and enantioselectivities.

Synthesis of Cyclic Fragrances via Transformations of Alkenes, Alkynes and Enynes: Strategies and Recent Progress

With increasing demand for customized commodities and the greater insight and understanding of olfaction, the synthesis of fragrances with diverse structures and odor characters has become a core task. Recent progress in organic synthesis and catalysis enables the rapid construction of carbocycles and heterocycles from readily available unsaturated molecular building blocks, with increased selectivity, atom economy, sustainability and product diversity. In this review, synthetic methods for creating cyclic fragrances, including both natural and synthetic ones, will be discussed, with a focus on the key transformations of alkenes, alkynes, dienes and enynes. Several strategies will be discussed, including cycloaddition, catalytic cyclization, ring-closing metathesis, intramolecular addition, and rearrangement reactions. Representative examples and the featured olfactory investigations will be highlighted, along with some perspectives on future developments in this area.

Crystal structure of 2,6-di-tert-butyl-4-(4-chlorobenzylidene)cyclohexa-2,5-dien-1-one, C21H25ClO

C21H25ClO, orthorhombic, Pna21 (no. 33), a = 14.152(2) Å, b = 22.112(3) Å, c = 6.0109(7) Å, V = 1880.9(4) Å3, Z = 4, R gt (F) = 0.0586, wR ref(F 2) = 0.1227, T = 150 K.