Acid‐Catalyzed Direct Conjugate Alkenylation of α,β‐Unsaturated Ketones

Abstract

Neue Kniffe, alte Reaktion: Ohne Übergangsmetalle und unter milden Bedingungen überführt die Titelreaktion eine Bandbreite von Substraten in γ,δ‐ungesättigte Ketone (siehe Schema; Tf=Trifluormethansulfonyl). Der Siliciumsubstituent in β‐Stellung am Enon ist entscheidend für die hyperkonjugative Stabilisierung des kationischen Intermediats.

Stereoselective Construction of 1,3‐Disilylcyclopentane Derivatives by Scandium‐Catalyzed [3+2] Cycloaddition of Allylsilanes to β‐Silylenones

“…The use of other triflate salts of transition‐metal or main‐group metals, such as indium, gallium, or bismuth, led to lower yields of cycloadduct 3 a than obtained with scandium (entries 5–7) 8. Trimethylsilyl triflate (Me 3 SiOTf) and triflic acid (HOTf) both showed very low catalytic activity, which is in contrast to the reported direct alkenylation reaction (entries 8 and 9) 9. 10 Surprisingly, the product selectivity changed dramatically with the use of a stoichiometric amount of titanium chloride (TiCl 4 ); under these conditions, allylation product 4 a was obtained as the major product in 76 % yield (entry 10).…”

Taming Living Carbocations in Catalytic Direct Conjugate Addition of Simple Alkenes to α,β‐Enones

“…Previously, a stoichiometric amount of Lewis acid was reported to promote the addition of alkenes to α,β‐enones to give also double‐bond‐shifted products 7. Recently, an intermolecular version was realized with a special class of enones and in this case a silyl group was introduced onto the β‐position of enones in order to facilitate β‐proton elimination 8. General methods for the intermolecular addition of simple alkenes to α,β‐enones remains elusive so far.…”

“…[7] Recently, an intermolecular version was realized with a special class of enones and in this case a silyl group was introduced onto the b-position of enones in order to facilitate b-proton elimination. [8] General methods for the intermolecular addition of simple alkenes to a,b-enones remains elusive so far.…”