19756-08-2Relevant academic research and scientific papers
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.
Palladium(0)-catalyzed enantioselective O,S-rearrangement of racemic O-allylic thiocarbamates: A new entry to enantioenriched allylic sulfur compounds
Gais, Hans-Joachim,Boehme, Achim
, p. 1153 - 1161 (2007/10/03)
Reaction of (±)-(E)-pent-3-en-2-ol, (±)-(E)-hept-4-en-3-ol, (±)-(E)-2,6-dimethylhept-4-en-3-ol, (±)-cyclohex-2-en-1-ol, and (±)-cyclohept-2-en-1-ol with methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, and benzyl isothiocyanate gave the corresponding racemic O-allylic thiocarbamates of medium to good thermal stability in good yields. The palladium(0)-catalyzed rearrangement of the (±)-(E)-pent-3-en-2-ol-, (±)-(E)-hept-4-en-3-ol-, (±)-cyclohex-2-en-1-ol-, and (±)-cyclohept-2-en-1-ol-derived O-allylic thiocarbamates at room temperature in methylene chloride by using Pd2(dba)3·CHCl3 (dba = dibenzylideneacetone) as precatalyst and (+)-(1R,2R)-1,2-bis-N-((2-(diphenylphosphino)benzoyl)-1,2-diaminocyclohexane as ligand for the palladium atom proceeded quantitatively and gave the corresponding acyclic (R)-configured S-allylic thiocarbamates and the cyclic (S)-configured S-allylic thiocarbamates with ee values ranging from 85% to ≥99% in yields of 76-94%. Rearrangement of the O-allylic thiocarbamates carrying a methyl group at the N atom not only was the fastest but also proceeded with the highest enantioselectivity. No rearrangement was observed under these conditions in the case of the racemic N-methyl O-allylic thiocarbamate derived from (±)-2,6-dimethylhept-4-en-3-ol, which has a branched carbon skeleton. (S)-Cyclohex-2-enethiol of 97% ee was obtained through hydrolysis of the corresponding N-methyl S-allylic thiocarbamate. 2-((R)-(E)-1-Methylbut-2-enylsulfanyl)pyrimidine of 91% ee and 2-((S)-cyclohex-2-enylsulfanyl)pyrimidine of 97% ee were synthesized in one synthetic operation from the corresponding N-methyl S-allylic thiocarbamates and 2-chloropyrimidine. Similarly, (S)-cyclohex-2-enylsulfanyl)benzene of 97% ee was obtained in one synthetic operation from the corresponding N-methyl S-allylic thiocarbamate through a palladium(0)-catalyzed substitution of iodobenzene in the presence of a base. The palladium(0)-catalyzed enantioselective rearrangement of O-allylic carbamates to S-allylic carbamates has been extended from the solution phase to the solid phase by using a methyl thioisocyanate polystyrene resin. In the case investigated the enantioselectivity of the rearrangement on the solid phase was considerably lower than that in solution.
Synthesis of enantiomerically enriched tertiary 2-cyclohexene-1-thiols via configurationally stable α-thio-substituted allyllithium compounds
Marr, Felix,Hoppe, Dieter
, p. 4217 - 4220 (2007/10/03)
(Equation presented) (S)-S-(2-Cyclohexenyl) N,N-diisopropylmonothiocarbamate [(-)-(S)-8] was deprotonated by sec-butyllithium/TMEDA to form a configurationally stable lithium compound (S)-9, which is the first example of a new class of α-thio-substituted
The synthesis and configurational stability of enantioenriched α-thioallyllithium compounds and the stereochemical course of their electrophilic substitution
Marr, Felix,Froehlich, Roland,Wibbeling, Birgit,Diedrich, Christian,Hoppe, Dieter
, p. 2970 - 2988 (2007/10/03)
Deprotonation of enantioenriched S-allyl N-monoalkylmonothiocarbamates furnished the corresponding chiral lithium compounds. The α-thioallyllithium compounds 9 and 25 were found to be configurationally stable in THF solutions at -78 °C. These represent the first configurationally stable α-thio-substituted allyllithium compounds, and they can be utilized in asymmetric synthesis. Alkylations proceeded with stereo-inversion or in an anti-SE′ process, while addition to carbonyl compounds took place in a syn-SE′ process. Hydroxyalkylation products were employed as starting material for Ni0-catalyzed cross-coupling reactions.
Palladium(0) catalyzed enantioselective rearrangement of O-allylic thiocarbamates to S-allylic thiocarbamates: Asymmetric synthesis of allylic thiols
Boehme, Achim,Gais, Hans-Joachim
, p. 2511 - 2514 (2007/10/03)
The Pd(0) catalyzed rearrangement of the O-allylic thiocarbamates rac- 2a, rac-2b and rac-4 in the presence of the chiral bisphosphane 5 proceeded quantitatively and gave the S-allylic thiocarbamates 6a, 6b and 7, respectively, with 91, 92 and 97% ee, res
Flash vacuum thermolysis - Synthesis and characterization of unstabilized cycloalkenethiones
Briard, Emmanuelle,Levillain, Jocelyne,Ripoll, Jean-Louis,Dat, Yves,Marcual, Albert,Lange, Catherine
, p. 869 - 874 (2007/10/03)
The flash vacuum thermolysis (FVT) of cydoalkenyl allyl (or propargyl) sulfides 8, 9, 12, and 13 led, as the main thermal pathway, to the conjugated cycloalkenethiones 1, 3, and 5, resulting from a retro-ene reaction. These reactive thioketones, thus obtained in ca. 70% yield, have been characterized in the gas phase by mass spectrometry, and at low temperature by IR, UV/Vis and NMR spectroscopy. The polymerization of 1, 3, and 5 upon warming is generally more rapid than the other attempted reactions and only the [2 + 3] dipolar cycloaddition with diazomethane led in low yield, besides polymeric materials, to isomeric 1,3-dithiolanes 20 from cyclopentenethione 1. The obtention of the nonconjugated cycloalkenethiones 2 and 4, expected in the FVT of sulfides 10 and 11, has been confirmed only by UV/Vis spectroscopy at -196 °C, due to their rapid enethiolization. In the case of the large-ring sulfide 14, the (E) geometry of the double bond favoured the competitive retro-ene reaction yielding cyclododecene and propynethial; on the other hand, the FVT of the tricyclic gem-dithiol 15, a possible precursor of cyclobutenethione (7), led to vinyl thioketene (18), obtained by thermal ring opening of 7.
Investigation of the Chemo- and Stereoselectivity of the Ketene-Claisen Rearrangement
Ernst, Beat,Gonda, Jozef,Jeschke, Rainer,Nubbemeyer, Udo,Oehrlein, Reinhold,Bellus, Daniel
, p. 876 - 891 (2007/10/03)
A novel type of ketene-Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellen
STEREOSELECTIVE KETENE-CLAISEN REARRANGEMENT OF CHIRAL ALLYLTHIOETHERS
Oehrlein, Reinhold,Jeschke, Rainer,Ernst, Beat,Bellus, Daniel
, p. 3517 - 3520 (2007/10/02)
A new method for the preparation of chiral β-branched, γ,δ-unsaturated thioesters and derivatives is presented, which involves the ketene-Claisen rearrangement of chiral allylthioethers.A novel synthesis of the starting chiral allylthioethers is also desc
