31001-80-6Relevant academic research and scientific papers
Highly enantioselective synthesis of 3-substituted furanones by palladium-catalyzed kinetic resolution of unsymmetrical allyl acetates
Mao, Bin,Ji, Yining,Fananas-Mastral, Martin,Caroli, Giuseppe,Meetsma, Auke,Feringa, Ben L.
supporting information; experimental part, p. 3168 - 3173 (2012/05/05)
Resolving the issue: A near-perfect Pd-catalyzed kinetic resolution of 1,3-disubstituted unsymmetrical allylic acetates uses silyl enol ethers as nucleophiles to access the important 3-substituted-furanone scaffold (see scheme; DACH=diaminocyclohexyl, dba=dibenzylideneacetone). The reaction proceeds under mild conditions and provides the desired products with excellent chemo-, regio-, and enantioselectivity. Copyright
Multiphoton infrared initiated thermal reactions of esters: Pseudopericyclic eight-centered cis-elimination
Ji, Hua,Li, Li,Xu, Xiaolian,Ham, Sihyun,Hammad, Loubna A.,Birney, David M.
supporting information; experimental part, p. 528 - 537 (2009/06/28)
Multiphoton infrared absorption from a focused, pulsed CO2 laser was used to initiate gas-phase thermal reactions of cis- and trans-3-penten-2-yl acetate. By varying the helium buffer gas pressure, it was possible to deduce the product distribution from the initial unimolecular reactions, separate from secondary reactions in a thermal cascade. Thus, trans-3-penten-2-yl acetate gives 54 ± 5% of β-elimination to give trans-1,3-pentadiene, 40 ± 3% of [3,3]-sigmatropic rearrangement to give cis-3-penten-2-yl acetate and 6 ± 4% of cis-1,3-pentadiene. Similar irradiation of cis-3-penten-2-yl acetate gives 45 ± 1% of β-elimination to give cis-1,3-pentadiene, 32 ± 2% of [3,3]-sigmatropic rearrangement to give trans-3-penten-2-yl acetate and 23 ± 2% of trans-1,3-pentadiene. The latter process is an eight-centered δ-elimination, which is argued to be a pseudopericyclic reaction. Although β-eliminations have been suggested to be pericyclic, B3LYP/ 6-31G(d,p), MP2 and MP4 calculations suggest that both β- and δ-eliminations, as well as [3,3]-sigmatropic rearrangements of esters are primarily pseudopericyclic in character, as judged by both geometrical, energetic and transition state aromaticity (NICS) criteria. Small distortions from the ideal pseudopericyclic geometries are argued to reflect small pericyclic contributions. It is further argued that when both pericyclic and pseudopericyclic orbital topologies are allowed and geometrically feasible, the calculated transition state may be the result of proportional mixing of the two states; this offers an explanation of the range of pseudopericyclic and pericyclic characters found in related reactions.
Palladium-catalyzed enantioselective allylic alkylation of thiocarboxylate ions: Asymmetri synthesis of allylic thioesters and memory effect/dynamic kinetic resolution of allylic esters
Luessem, Bernhard J.,Gais, Hans-Joachim
, p. 4041 - 4052 (2007/10/03)
The palladium-catalyzed allylic alkylation of KSAc and KSBz with racemic cyclic and acyclic allylic esters by using N,N'-(1R,2R)-1,2-cyclohexandiylbis[2-(diphenylphosphino)-benzamide] as ligand frequently gave the corresponding allylic thioesters with high ee values and yields. The reaction of the cyclic allylic carbonates with KSAc in the presence of H20 was accompanied by a partial palladium-catalyzed enantioselective "hydrolysis" of the substrates with formation of the corresponding enantioenriched allylic alcohols. The degree of the "hydrolysis" was strongly dependent on the solvent and the thiocarboxylate ion. Highly selective kinetic resolutions (KRs) were observed in the palladium-catalyzed reaction of the racemic cyclohexenyl and cycloheptenyl acetates with KSAc. While the KR of the cyclohexenyl acetate is characterized by a selectivity factor S = 72 ± 19, that of the cycloheptenyl acetate afforded (R)-cycloheptenyl acetate of ≥ 99% ee in 48% yield and (S)-cycloheptenyl thioacetate of 98% ee in 50% yield. The palladium-catalyzed reaction of the racemic cyclopentenyl acetate with KSAc showed a strong "memory effect" (ME), that is, both enantiomers reacted with different enantioselectivities. The ME was probed by studying the palladium-catalyzed reactions of both the matched acetate of ≥ 99% ee and the mismatched acetate of ≥ 99% ee with KSAc. The acetates not only reacted with different enantioselectivities and rates but also suffered an unexpected and concomitant palladium-catalyzed racemization in the presence of the chiral ligand. This led in the case of the mismatched acetate to a temporary dynamic kinetic resolution (DKR) that featured a racemization of the mismatched acetate by the chiral catalyst. Studies of the palladium-catalyzed reaction of the racemic cyclopentenyl acetate, carbonate, and naphthoate with KSAc in the presence of the chiral ligand also showed the ME to be strongly dependent on the nucleofuge. This also allowed the synthesis of (S)-cyclopentenyl thioacetate of 92% ee in high yield from the racemic cyclopentenyl naphthoate.
