80251-68-9Relevant academic research and scientific papers
Photochemical Organocatalytic Regio- and Enantioselective Conjugate Addition of Allyl Groups to Enals
Berger, Martin,Carboni, Davide,Melchiorre, Paolo
, p. 26373 - 26377 (2021/11/16)
We report the first catalytic enantioselective conjugate addition of allyl groups to α,β-unsaturated aldehydes. The chemistry exploits the visible-light-excitation of chiral iminium ions to activate allyl silanes towards the formation of allylic radicals, which are then intercepted stereoselectively. The underlying radical mechanism of this process overcomes the poor regio- and chemoselectivity that traditionally affects the conjugate allylation of enals proceeding via polar pathways. We also demonstrate how this organocatalytic strategy could selectively install a valuable prenyl fragment at the β-carbon of enals.
The reactivity of epoxides with lithium 2,2,6,6-tetramethylpiperidide in combination with organolithiums or grignard reagents
Hodgson, David M.,Fleming, Matthew J.,Stanway, Steven J.
, p. 4763 - 4773 (2008/02/04)
(Chemical Equation Presented) The scope and limitations of lithium 2,2,6,6-tetramethylpiperidide (LTMP)-modified reductive alkylation of epoxides is detailed. A variety of organolithiums are added to terminal and 2,2-disubstituted epoxides in the presence of LTMP to generate alkenes in a completely regio- and highly stereoselective manner. Arylated alkenes, dienes, allylsilanes, and enynes are accessed using this procedure. The methodology is applied in the synthesis of the roller leaf moth pheromone, (3E,5Z)-dodecadienyl acetate. The corresponding reaction without LTMP has also been examined, and a study using deuterated epoxides provides insight into the mechanism. In the presence of LTMP, Grignard reagents are also shown to produce E-alkenes directly from epoxides.
Stereoselective Synthesis of (E)- and (Z)-2-Alkenyltrimethylsilanes from 1,2-Epoxy-1,3-bis(trimethylsilyl)propane
Shimizu, Nobujiro,Imazu, Sachiko,Shibata, Fumihiro,Tsuno, Yuho
, p. 1122 - 1128 (2007/10/02)
Stereoselective synthesis of various (E)- and (Z)-2-alkenyltrimethylsilanes (RCH=CHCH2SiMe3; R=Me, Et, n-Bu, i-Pr, c-hexyl, t-butyl, and phenyl) has been accomplished by a reaction of 1,2-epoxy-1,3-bis(trimethylsilyl)propane with Grignard reagents (RMgX) followed by subsequent Peterson olefination reactions of resulting 1,2-bis(trimethylsilyl)-3-alkanols ; the acid (BF3OEt2 or HClO4)-catalyzed olefination yields the (E)-isomer, while the base (KH or NaH)-induced olefination yields the (Z)-isomer in more than 95 percent stereochemical purity in most cases.
Photochemical reactivity of α-phenyl β,γ-enones. Singlet 1,3-acyl shift, triplet aromatic di-?-methane (DPM) rearrangement and triplet aryl-carbonyl bridging
Koppes, Margareth J. C. M.,Beentjes, Peter C. J.,Cerfontain, Hans
, p. 313 - 324 (2007/10/02)
The photochemistry of the series of α-phenyl β,γ-enones 6-10 has been studied under conditions of both direct (λ 300 nm) and triplet-sensitized irradiation with the aim of determining the reactivity patterns of these "multi"-chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ-enones, viz. the 1,3-acyl shift, affording the corresponding (E)- and (Z)-5-phenyl-4-hexen-3-ones, decarbonylation of the radicals formed by α-cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet-excited state yielding small amounts of the corresponding acetophenones.The acetophenones are thought to be formed by initial β-bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4- or 1,3-oxa-diradical.Upon sensitized irradiation, the o-methoxy- and p-cyano-substituted reactants 9 and 10 exhibit the di-?-methane rearrangement, leading to mixtures of the corresponding cis- and trans-1-acetyl-1-methyl-2-phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively.The formation of the 1,3-AS and decarbonylation products illustrates the occurrence of α-cleavage, whereas the acetophenones and di-?-methane products are formed via initial aryl-carbonyl and aryl-vinyl bridging, respectively.The inability of the other α-phenyl β,γ-enones to undergo photocyclopropanation is discussed in terms of excitation-energy partition.In the o-methoxy and p-cyano-substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ-enone moiety.Subsequent triplet-energy dissipation by a free-rotor mechanism would then account for the stability of these systems.This was observed for (E)-7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
