Asymmetric Synthesis of the Epimeric (3S)-3-((E)-Hex-1-enyl)-2-methylcyclohexanones

Abstract

Abstract:The asymmetric rhodium-catalysed 1,4-addition of alkenylzirconium reagents to 2-cyclohexenone can be useful in the synthesis of 3-alkenyl-2-methylcyclohexanones, provided that formaldehyde is used in trapping the intermediate zirconium enolates. In this manner a four-step sequence leading to the two epimeric 3-hexenyl-2-methylcyclohexanones in enantiomeric form was developed.

Asymmetric Transition-Metal Catalysis in the Formation and Functionalization of Metal Enolates

“… De Clercq has used gaseous formaldehyde as a trapping reagent for the Zr enolate 128 . The resulting products were obtained in 89% yield with a diastereoselectivity of 2.7:1 and an ee of up to 96% by using the catalytic system [Rh­(cod)­Cl] 2 / L21 …”

“…The resulting products were obtained in 89% yield with a diastereoselectivity of 2.7:1 and an ee of up to 96% by using the catalytic system [Rh(cod)Cl] 2 /L21. 131 Although indium enolates represent a less explored area in organic chemistry, there was a report of a Rh-catalyzed CA of diarylindium(III) hydroxides to various Michael acceptors. 132 ■ BASE-GENERATED ENOLATES Uncatalyzed reactions of enolates with alkyl halides are common, but the reaction with aryl or alkenyl halide is usually slow and needs a transition-metal catalyst to proceed efficiently.…”

Development of Analogues of 1α,25‐Dihydroxyvitamin D3 with Biased Side‐Chain Orientation: C20 Methylated Des‐C,D‐homo Analogues

“…The synthesis of cyclohexanone 10a (and 10b ) has been reported in detail and is summarized in Scheme 12. It features the highly enantioselective 1,4‐addition of an alkenylzirconocene chloride to 2‐cyclohexenone by a chiralrhodium(I) complex generated with BINAP as chiral ligand, a methodology which has led to the synthesis of enantiomerically pure 16 13.…”

Production of detoxified sorghum straw hydrolysates for fermentative purposes

“…Unfortunately, such zirconium enolates offer only a limited scope of subsequent transformations. Aldol reactions25 as well as α‐selenylation26 have been achieved, yet it is impossible to introduce an alkyl or allyl group by nucleophilic substitution 17d,25a,26. On the contrary, Oi, Inoue et al.…”

“…Under Rh catalysis, addition of alkenylboron14 and ‐silicon reagents15 is again performed in protic media which interferes with subsequent trapping reactions. On the contrary, alkenylstannanes16 and ‐zirconocenes17 have been employed under water‐free conditions, and conjugate addition of the latter ones has been coupled with subsequent aldol reactions, albeit with only moderate diastereoselectivities 17c,d…”