36566-80-0Relevant academic research and scientific papers
Thermal isomerisations, XXIV. Gas phase kinetics of the pyrolysis of some 3,3-dimethyl-1-alkyl-cyclopropenes: Some surprising substituent activation effects and the intramolecular trapping of vinylidene intermediates
Hopf, Henning,Plagens, Andreas,Walsh, Robin
, p. 825 - 835 (2007/10/03)
The gas phase pyrolyses of four 3,3-dimethyl-1-alkylcyclopropenes were studied for which the 1-alkyl substituents are ethyl- (6), isopropyl- (7), 1′-butyl- (8) and 1′-isoamyl- (9). Rate data over a 50°C temperature range were obtained and Arrhenius parameters are reported both for overall reactions and individual pathways for all compounds. Tests confirm all reactions to be unimolecular and homogeneous. For 8 and 9, noteworthy products are cyclopentenes, whose presence demonstrates the involvement of vinylidene intermediates. The substantial product yields of 2,4-alkadienes together with dramatic rate enhancement effects of these 1-alkyl substituents (relative to 1-methyl) are explained by the involvement of vinylcarbene intermediates in this pathway. Minor, transient products from 6, 8 and 9 are probably isomeric cyclopropenes. This suggests further pathways for vinylidene intermediates, whose reactivity pattern is briefly reviewed. VCH Verlagsgesellschaft mbH, 1996.
Synthetic Microbial Chemistry, XXVI. - Absolute Configuration of (+)-Xanthocidin as Determined by the Synthesis of Its Enantiomers of Known Stereochemistry
Mori, Kenji,Horinaka, Akio,Kido, Masaru
, p. 817 - 826 (2007/10/02)
The absolute configuration of the antibiotic (+)-xanthocidin (4,5-dihydroxy-5-isopropyl-4-methyl-2-methylene-3-oxocyclopentane-1-carboxylic acid, 1) was shown to be 1R,4S,5S by the synthesis of its enantiomers.Lipase AK (Amano) was used for the key resolution step, and the absolute configuration of the resolved intermediate (+)-16 was determined by X-ray analysis of its (1S)-camphanic ester (+)-20. - Key Words: Antibiotics / Asymmetric acylation / Lipases / Streptomyces xanthocidicus / Xanthocidin
Stereoselective synthesis of vicinal dilithioalkenes by addition of lithium metal, to carbon-carbon triple bonds
Maercker,Girreser
, p. 8019 - 8034 (2007/10/02)
The reaction of various cyclic and acyclic alkynes with lithium dust (2% sodium) to form vicinal dilithioalkenes has been investigated. Aliphatic alkynes, e.g. 3-hexyne (27a), exclusively afford the corresponding (E)-dilithioalkenes, insoluble solids which are stable at room temperature and allow access to a variety of tetrasubstituted olefins in acceptable yields.
THE ELECTRON SPIN RESONANCE SPECTRA OF THE ANNULENE (CYCLOBUTADIENE) RADICAL CATIONS, R4C4+.
Courtneidge, John L.,Davies, Alwyn G.,Lusztyk, Ewa,Lusztyk, Janusz
, p. 155 - 164 (2007/10/02)
A series of simple (R=R') and mixed (RR') cyclobutadiene radical cations, R2R'2C4+., have been prepared by photolysis of the alkynes, RCCR' or of mixtures of the alkynes RCCR and R'CCR', in dichloromethane in the presence of aluminium chloride, and the e.s.r. spectra have been recorded.The magnitude of the 13C hyperfine coupling in Et4C4+. confirms that it is a ?-radical, with no evidence for out-of-plane or in-plane (Jahn-Teller) distortion.The values of a(Hβ) for the radicals (RCH2)4C4+. and (RCH2)2R'2C4+. indicate that, as the bulk of the alkyl substituents increases, the group R is pushed out of the plane of the ring.Some unusual temperature effects on a(Hβ) are ascribed to interaction of the radical cation with the solvent or with the counterion.As the bulk of the alkyl groups increases, the g-value decreases from 2.0030 to about 2.0022. cis- and trans-Isomers of the radicals Me2tBu2C4+., Et2tBu2C4+., iBu2tBu2C4+., and propably Me2Et2C4+. have been identified, and the spectra of cis- and trans-Me2tBu2C+. are analysed in terms of breaking of the degeneracy of the molecular orbitals of the cyclobutadiene system by differential electron release by the alkyl groups (tBu > Me).
