50592-72-8Relevant academic research and scientific papers
Mild TiIII- and Mn/ZrIV-catalytic reductive coupling of allylic halides: Efficient synthesis of symmetric terpenes
Barrero, Alejandro F.,Herrador, M. Mar,Quilez Del Moral, Jose F.,Arteaga, Pilar,Arteaga, Jesus F.,Dieguez, Horacio R.,Sanchez, Elena M.
, p. 2988 - 2995 (2007/10/03)
(Chemical Equation Presented) Two new efficient methods for the regioselective homocoupling of allylic halides using either catalytic Ti III or the combination Mn/ZrIV catalyst have been developed. The regio- and stereoselectivity of the process proved to increase significantly when the Mn/ZrIV catalyst is used as the coupling reagent and when cyclic substituted allylic halides are used as substrates. The use of Lewis acids such as collidine hydrochloride allowed the quantity of catalyst to be lowered up to 0.05 equiv. We have proved the utility of these protocols with the synthesis of different terpenoids such as (+)-β-onoceradiene (1), (+)-β-onocerine (2), squalene (5), and advanced key-intermediates in the syntheses of (+)-cymbodiacetal (3) and dimeric ent-kauranoids as xindongnin M (4a).
Radical-Stabilization-Energy - the MMEVBH Force Field
Roth, Wolfgang R.,Staemmler, Volker,Neumann, Martin,Schmuck, Carsten
, p. 1061 - 1118 (2007/10/02)
Making use of the VB method of Malrieu et al. a force field has been developed, which allows to calculate heats of formation of hydrocarbons (conjugated and non-conjugated olefins, radicals and diradicals) with high accuracy.With this method radical stabilization energies (RSE) for a great number of delocalized radicals are calculated and compared with experimental values, derived from shock-tube measurements of dissociation energies or from rotational barriers of substituted olefins.A detailed analysis of the RSE with respect to structure, substituents, strain, and aromaticity is presented. - Key Words: Resonance energy / Heats of formation / Single pulse shock tube / Intrisic rotational barrier
On the Regioselectivity of Coupling of Substituted Allyl Radicals. Steric Versus FMO Control
Pasto, Daniel J.,L'Hermine, Gael
, p. 3259 - 3272 (2007/10/02)
The photo-induced decomposition of substituted-homoallylic 4-nitrobenzenesulfenates produces substituted allyl radicals which undergo dimerization and coupling with the 4-nitrobenzenethiyl radical.The regioselectivity of the dimerization of the allyl redi
Evidence for a free radical mechanism in the decomposition of bis(but-2-enyl)tellurium
Stevenson, John,Bell, William,Ferry, Joseph,Cole-Hamilton, David J.,Hails, Janet E.
, p. 141 - 145 (2007/10/02)
Reactions of basic aqueous solution of Na2Te with MeCH=CHCH2Br or CH2=CHCHMeCl give ZZ-, ZE- and EE(MeCH=CHCH2)2.This is interpreted in terms of a mechanism involving attack of Na2Te on the 2-butenyl cation formed from the allyl halide under the basic reaction conditions.The rate of reaction to give the E-configuration is ca. 3 times that to form the Z.Decomposition of (MeCH=CHCH2)2Te in the liquid or gas phases gives all possible products arising from dimerization of the allyl group.This is interpreted in terms of homolytic fission of the Te-C bond followed by coupling of the allyl radicals formed, particularly as no compounds containing CH2-CHCHMeTe are recovered after partial pyrolysis.The products can be fitted to a purely statistical model in which the reactivity ratio of the primary to secondary allyl is ca. 0.63:0.37.The statistical fit is taken to indicate that mechanism other than that involving homolytic fission and free radical coupling play a negligible part.
SPECIFIC ALLYLIC-ALLYLIC COUPLING PROCEDURES EFFECTED BY LIGAND-INDUCED ELIMINATION FROM DI(ALLYLIC)PALLADIUM SPECIES
Goliaszewski, Alan,Schwartz, Jeffrey
, p. 5779 - 5790 (2007/10/02)
Bis(allylic)palladium complexes can be induced to undergo reductive elimination by replacement of phosphine ligands in the system with ?-acidic ligands.The product 1,5-dienes, formed in high yield, are predominantly the 'head-to-head' coupled isomers.The bis(allylic)palladium intermediates may be formed by addition of an allylic Grignard or trialkyl(allylic)tin reagent to an(η3-allyl)palladium chloride complex, or by 1,3-diene condensation.The latter process leads to cyclodimerization, 'unusual' for palladium catalysed reactions.
Reaction Of Allylic Boron and Aluminium "Ate" Complexes with Organic Halides and Carbonyl Compounds. Trialkylboranes as Regio-, Stereo-, and Chemoselective Control Elements
Yamamoto, Yoshinori,Yatagai, Hidetaka,Maruyama, Kazuhiro
, p. 1969 - 1975 (2007/10/02)
Lithium allylic boron ate complexes, prepared by the addition of trilakylboranes to an ether solution of allylic lithium compounds, regioselectively react with allylic halides to produce head-to-tail 1,5-dienes (eq 1).The ate complexes are also prepared from the reaction of allylic boranes with alkyllithium derivatives.Magnesium or copper allylic boron ate complexes are less effective.Lithium crotyl boron ate complexes undergo a rapid reaction with aldehydes with good threoselectivity (eq 2).The selectivity is affected by the steric hindrance of trialkylboranes, as explained by the steric parameters of the 6-membered transition state.The ate complexes react with α,β-unsaturated ketones in a competitive manner of 1,2 and 1,4 addition, while they add to cinnamaldehyde exclusively in a 1,2 manner.The chemoselective aspects are only investigated. 1H and 13 C NMR spectra of lithium allylic boron ate complexes clearly indicate (i) the prevention of allylic rearrangement, (ii) the predominant trans geometry of the crotyl unit in comparison with the corresponding trivalent crotylboron, and (iii) the relative importance of ?-? conjugation between the double bond and the carbon-boron bond (eq 3).
(Alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium Complexes
Lehmkuhl, Herbert,Fustero, Santos
, p. 1353 - 1360 (2007/10/02)
Bis(η5-cyclopentadienyl)titanium hydride (Cp2TiH), presumably formed in situ from bis(η5-cyclopentadienyl)titanium dichloride (1) and isopropylmagnesium bromide (2) adds to the conjugated C=C bonds of the alkatrienes 4, 5, 25, 36, and 45 to give the (alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium complexes 7 and 10, 8, 26, and 30, 37, 46.The complexes 7, 8, and 26 with the alkenyl group in position 1 isomerize to give the compounds 27, 28, and 29 in which the C=C bond is conjugated with the allyl group.Compound 37 which contains an alkenyl group in a meso-position does not isomerize.In the case of isomycoren (40), TiH addition occurs primarily to the isolated C=C bond followed by intramolecular cyclization to give the bis(η5-cyclopentadienyl)(1-cyclopentyl-η3-allyl)titanium complex 41.
