- Preparation of α-haloacrylate derivatives via dimethyl sulfoxide-mediated selective dehydrohalogenation
-
(Chemical Equation Presented) Dimethyl sulfoxide causes α/β-dihalopropanoate derivatives to undergo efficient, selective dehydrohalogenation to form α-haloacrylate analogues. A variety of α-halo Michael acceptors were prepared in dimethyl sulfoxide under mild, base-free conditions, including the preparation of α-bromoacrolein and α-chloro- and bromoacrylonitriles. Synthesis of these molecules has been reported in the literature to be difficult. Among all the existing dehydrohalogenation procedures, this protocol is the most facile, practical, and environmentally benign process.
- Li, Wei,Li, Jianchang,Wan, Zhao-Kui,Wu, Junjun,Massefski, Walter
-
p. 4607 - 4610
(2008/03/13)
-
- AZOLE INHIBITORS OF CYTOKINE PRODUCTION
-
Compounds having the formula are useful for treating diseases that are prevented by or ameliorated with Interleukin-2, Interleukin-4, or Interleukin-5 production inhibitors.
- -
-
-
- Thienylpyrrole fungicidal agents
-
There are provided fungicidal thienyl- and furylpyrrole compounds of formula I STR1 Further provided are compositions and methods comprising those compounds for the protection of plants from fungal infestation and disease.
- -
-
-
- Thienyl-and furylpyrrole insecticidal and acaricidal agents
-
There are provided thienyl- and furylpyrrole compounds of formula I STR1 and their use for the control of insects and acarina. Further provided are compositions and methods comprising those compounds for the protection of plants from attack by insects and acarina.
- -
-
-
- Elimination reactions: Experimental confirmation of the predicted elimination of (β-cyanoethyl)sulfonium ions through a concerted, E2 mechanism
-
Extrapolation of the lifetimes of carbanion intermediates formed in the elimination reactions of a series of β-cyanoethyl thioethers with different leaving groups (J. Am. Chem. Soc. 1988, 110, 5087-5095) predicts that the carbanions will not have a significant lifetime for pKlg a 2SO/H2O, 25.0 °C). Values of βlg obtained from Br?nsted-type plots of log kB against the estimated pKa values of the leaving groups, decrease from 0.39 to 0.24 with increasing pKa of the base catalyst. The changes in β and βlg are described by the interaction coefficient pxy=d?βlg/?pK BH=?βlg/?KBH=0.026. The deuterium isotope effect for proton removal from Ph-S+(Me)-CH2CL2CN is kH/kD=4.4 and 4.9 for tris(hydroxymethyl)aminomethane and ethylamine buffers, respectively, and there is no detectable protium exchange into the deuterated substrate. The positive pxy coefficient provides evidence for coupling between proton abstraction and leaving group expulsion; it confirms the concerted AxhDHDN (E2) mechanism. The values of β and βlg indicate an imbalance in the transition state, in which proton transfer is ahead of leaving group expulsion. The change from a stepwise AxhDHH+DNN (ElcB) mechanism for thiophenoxide leaving groups to a concerted mechanism for sulfide leaving groups is consistent with the notion that the mechanism is determined solely by the lifetime of the carbanion; there is no evidence for the coexistence of stepwise and concerted mechanisms.
- Banait, Narinder S.,Jencks, William P.
-
p. 6950 - 6958
(2007/10/02)
-
- Elimination reactions of β-Cyano Thioethers: Evidence for a Carbanion Intermediate and a Change in Rate-Limiting Step
-
The addition reactions of thiol anions to form adducts with acrylonitrile (1), 1-chloroacrylonitrile (2), and fumaronitrile (3) and the corresponding elimination reactions were examined in aqueous solution, generally containing 8.3percent Me2SO at 25 deg C.Deuterium exchange into the methanethiol and thiosalicylate adducts of 1 is faster than elimination.Deuterium exchange causes biphasic kinetics for elimination reactions in D2O of the p-nitrothiophenol, but not of the pentafluorothiophenol, adducts 1 and 2.The kinetic solvent deuterium isotope effects of knHOH/knDOD = 2.0 for addition of thiosalicylate to form 3 and 1.1-1.2 for addition of β-mercaptoethanol and thioacetic acid anions to form 1 are smaller than the product discrimination isotope effects of kH/kD = 3.2, 2.8 and 3.2 for these reactions.These differences show that the reactions proceed through a carbanion intermediate that is protonated faster than it expels basic thiol anions.These results exclude a concerted mechanism for addition-elimination with a concurrent, separate exchange reaction.The solvent kinetic deuterium isotope effect is 3.9 for the addition of thionitrobenzoate dianion to form 3.Buffer catalysis of elimination becomes more significant with more acidic leaving groups and is larger for 3 than for 1 with a given leaving group.The results show that the rate-limiting step changes from addition-elimination of the thiol anion to proton transfer with decreasing pKa of the thiol; the same change is favored by addition of CN to the α-position for a given thiol.The effect of the α-CN group is attributed to conjugation with the developing double bond in the transition state for elimination.The Broensted slope is β = 0.90 for rate-limiting deprotonation of the pentafluorothiophenol adduct 3 and Broensted-type plots against the pKa of the leaving group have slopes of β1g = -0.25 and -0.54 for predominantly rate-limiting deprotonation and leaving group expulsion, respectively.
- Fishbein, James C.,Jencks, William P.
-
p. 5075 - 5086
(2007/10/02)
-
- Elimination Reactions of β-Cyano Thioethers: Internal Return and the Lifetime of the Carbanion Intermediate
-
The E1cB elimination reaction of the pentafluorothiophenol adduct of fumaronitrile (3) in water containing 8.3percent Me2SO shows strong buffer catalysis and primary deuterium isotope effects of kH/kD = 4-5.In contrast, hydrogen exchange of the methanethiol adduct of 3 shows little or no buffer catalysis.There is no incorporation of deuterium that gives an inverse solvent isotope effect in the buffer-catalyzed elimination of the thionitrobenzoate adduct of 3 in D2O and H2O, although thiol anion expulsion is partly rate limiting for this reaction.These observations are consistent with internal return of the abstracted proton from the protonated buffer base that is competitive with the expulsion of leaving groups with pKa > 4.The primary deuterium isotope effects for elimination catalyzed by hydroxide ion are kH/kD = 4.9 +/- 0.4, 4.2 +/- 0.1, 4.2 +/- 0.3, and 3.1 +/- 0.1 for the pentafluorothiophenol and thionitrobenzoate adducts of 3, the N-methyl-2-mercaptopyridinium ion adduct of acrylonitrile (1), and the pentafluorothiophenol adduct of chloroacrylonitrile (2), respectively.These isotope effects are significantly larger than values of kH/kD = 2.6 +/- 0.3, 2.2 +/- 0.1, and 2.1 +/- 0.1 for buffer-catalyzed elimination from the adducts of 1 and 3.They are also larger than (1) the primary isotope effects of kH/kD = 2.5 +/- 0.3, 2.3 +/- 0.2, and 2.3 +/- 0.2 for the p-nitrothiophenol adducts of 1 and 3 and the thiophenol adduct of 2 that were obtained from the biphasic kinetics for elimination of these compounds in D2O and (2) the product discrimination isotope effects of ca. 3 for the addition of thiol anions to 1 and 3.These observations are consistent with the formation of an unstable carbanion intermediate that undergoes competitive reprotonation by solvent, k-1, exchange of the abstracted proton with the bulk solvent, ks, and elimination, k2.Ratios of k-1/ks and k-1/k2 that were obtained from the results give values of k-1 ca. 1E11 s-1 and k2 = 1E10-1E13 s-1, assuming a value of ks = 1E11 s-1.Estimated pKa values in aqueous solution include 26.8 for NCCH2CH2SPh, 22.0 for NCCH(Cl)CH2SPhNO2, and 23.2 for NCCH2CH(CN)SCH3.
- Fishbein, James C.,Jencks, William P.
-
p. 5087 - 5095
(2007/10/02)
-
- Rearrangement Approaches to Cyclic Skeletons. IV. The Total Synthesis of (+/-)-Pinguisone and (+/-)-Deoxopinguisone Based on Photochemical Acyl Migration of a Bicyclonon-6-en-2-one
-
The total synthesis of (+/-)-Pinguisone (2) and (/-)-deoxopinguisone (3), fused ring sesquiterpenes, has been achieved starting from 1-methoxy-3,4,5-trimethylbenzene. 1-Methoxy-4,5,endo-8-trimethylbicyclonon-5-en-2-one (9) was prepared selectively via facial selective Diels-Alder reaction of the diene derived from the benzene and 2-chloroacrylonitrile.Ring enlargement of 9 using (CH3)3SiCHN2 and BF3 etherate gave the corresponding bicyclooct-en-2-one (8).The photochemical acyl migration of 8 gave the fused-ring compound (7).The fourth methyl was introduced selectively by the conjugate addition of (CH3)2CuLi to the spironon-8-ene-3,2'-dioxolan>-7-one prepared from 7.Each furan ring of 2 and 3 was constructed via the corresponding butenolide derived from the γ-keto acid by acid-catalyzed dehydration.
- Uyehara, Tadao,Kabasawa, Yasuhiro,Kato, Tadahiro
-
p. 2521 - 2528
(2007/10/02)
-
- (E-Z) ISOMERIZATION OF UNSATURATED NITRILES
-
Equilibrium data of the title isomerization of X-CH=CH-CN nitriles (X=Cl, CN, OR, SR) have been measured , and the respective ΔG values have been compared with the energy difference calculated by the CNDO/2 method.
- Prochazka, Milos,Zaruba, Arno
-
-
- Process for producing 2,3-dihalopropionitrile
-
A process for producing a 2,3-dihalopropionitrile is provided which comprises directly halogenating acrylonitrile with a halogenating agent in the presence of a carbonate, hydrogen carbonate or hydrogen phosphate of an alkali or alkaline earth metal and in the absence of positive irradiation of light.
- -
-
-
