93222-97-0Relevant academic research and scientific papers
Preparation of tert-Butyl-Capped Polyenes Containing up to 15 Double Bonds
Knoll, Konrad,Schrock, Richard R.
, p. 7989 - 8004 (2007/10/02)
7,8-Bis(trifluoromethyl)tricyclo2,5>deca-3,7,9-triene (TCDT) can be ring-opened in a controlled manner by W(CH-t-Bu)(NAr)(O-t-Bu)2 (Ar = 2,6-C6H3-i-Pr2) to give living oligomers from which the metal can be removed in a Wittig-like reaction with pivaldehyde or 4,4-dimethyl-trans-2-pentenal.Heating the oligomer yields a distribution of tetr-butyl-capped polyenes, (t-Bu)(CH=CH)n(t-Bu), where n is odd if pivaldehyde is used in the cleavage reaction or even if 4,4-dimethyl-trans-2-pentenal is used.Mixtures of odd and even polyenes have been analyzed byreserved-phase HPLC methods, and those having as many as 13 double bonds have been isolated by column chromatography on silica gel under dinitrogen at -40 deg C and characterized by (1)H and (13)C NMR and UV-vis studies.The 17-ene has been observed by HPLC.Polyenes containing more than 17 double bonds are relatively unstable under the reaction and subsequent isolation conditions; those containing between 11 and 15 double bonds decompose thermally progressively more readily.The initial isomer in the odd-ene series has largely the trans(cis,trans)x geometry as a result of stereospecific trans initiation, stereoselective trans propagation, stereospecific trans cleavage, and stereospecific cis retro-Diels-Alder reactions.The even-ene series is more complex since the Wittig-like reaction involving 4,4-dimethyl-trans-2-pentenal is not selective.UV-vis and (13)C and (1)H NMR data have been collected and analyzed in detail for the trans(cis,trans)x isomers for x = 1-5 (up to 11 double bonds) and for the odd and even all-trans forms containing up to nine double bonds.Extrapolation of a plot of the energy of the 1Bu 1Agg(0-0) transition versus 1/n (for up to the 13-ene) predicts that the HOMO-LUMO gap will be 1.79-1.80 eV for an infinite all-trans-polyene; in carbon disulfide it will be 1.56 eV.For the trans(cis,trans)x forms the 1Bu 1Agg(0-0) energy gap is predicted to be 1.95 eV for an infinite polyene in a mixture of acetonitrile, dichloromethane, and water (90:5:5).The ease of thermal cis-to-trans isomerization (ultimately to the all-trans form) correlates directly with chain length, isomerization to the all-trans form being especially facile for the 13-ene and beyond.The all-trans-polyenes are significantly less soluble than forms that contain one or more cis double bonds, although cross-linking cannot be ruled out as a contributor to insolubility for polyenes longer than the 13-ene.The retro-Diels-Alder reaction in the first unit away from the metal in living polyTCDT is accelerated 10 times relative to that in the second unit away from the metal.Heating polyTCDT gives living polyenes that are stable at 50 deg C for 45 min in solution; no benzene is formed.
Palladium- or Nickel-Catalyzed Reactions of Alkenylmetals with Unsaturated Organic Halides as a Selective Route to Arylated Alkenes and Conjugated Dienes: Scope, Limitations, and Mechanism
Negishi, Ei-ichi,Takahashi, Tamotsu,Baba, Shigeru,Horn, David E. Van,Okukado, Nobuhisa
, p. 2393 - 2401 (2007/10/02)
Stereo- and regiodefined alkenylmetals containing Al, Zr, and Zn react with aryl and alkenyl iodides and bromides in the presence of catalytic amounts of Pd or Ni complexes containing phosphine ligands, such as PPh3, to give the corresponding cross-coupled products.Palladium catalysts permit nearly 100 percent stereospecificity in both alkenyl-aryl and alkenyl-alkenyl coupling reactions, whereas nickel catalysts lead to partial stereochemical scrambling in the alkenyl-alkenyl coupling.Although many other metals including Li, Mg, Cd, Hg, B, Si, Sn, Ti, and Ce were also used, the results were inferior to those obtained with Al, Zr, and Zn under the conditions used in the present study.The turnover numbers for the palladium-catalyzed reactions of PhI with (E)-1-octenylmetals containing Al, Zr, and Zn were 2,3, and > 2000 mmol of (E)-1-octenylbenzene (8) per mmol of Pd(PPh3)4 per hour at room temperature, respectively.The stoichiometric reaction of PhPd(PPh3)2I (6) with 1.2 equiv of (E)-1-octenylzinc chloride (7) in a 2:1 mixture of CD2Cl2 and THF was examined in detail.The reaction follows second-order konetics (k2 = 2.9 L/(mol.min) at 0 deg C) to give 8 without the buildup of any intermediate.The results are consistent with a slow formation of 9 via transmetalation followed by its rapid reductive elmination to give 8 and "Pd(PPhe3)2".Addition of PhI to the reaction mixture rapidly gives 6 in 98 percent yield, supporting the plausibility of the proposed oxidative addition step.These results are consistent with the proposed mechanism consisting of oxidative addition of Pd(0) complexes, rate-determining transmetalation involving Pd(II) complexes, and rapid decomposition of diorganopalladium(II) species to produce the coupling products in one or more subsequent steps.The rate-determining transmetalation step provides an explanation for the effect of metals in organometallic reagents used stoichiometrically.
Hydroboration. 69. Hydroboration Characteristics of Lithium Borohydride/Ethyl Acetate in Ethyl Ether. A New System for Controlled Hydroboration of Alkenes and Alkynes
Brown, Herbert C.,Somayaji, Vishwanatha,Narasimhan, S.
, p. 4822 - 4827 (2007/10/02)
Alkenes and alkynes, which are normally inert to lithium borohydride, are readily hydroborated by this reagent in ethyl ether in the presence of carboxylic esters at 25 deg C.Alkenes form dialkylborinates while alkynes give rise either to vinylboranates or divinylborinates, depending upon the structure and reactivity of the alkyne and the stoichiometry of the reagent.This valuable intermediates are readily transformed into other organic derivatives, thus making this controlled hydroboration procedure a practical, valuable procedure in organic synthesis.
