Methyl Alkenes Research Articles

Semiochemicals for intraspecific communication of the fig weevil Aclees sp. cf. foveatus (Coleoptera: Curculionidae): a first survey

The fig tree weevil Aclees sp. cf. foveatus (Coleoptera: Curculionidae), introduced in Italy in 2005, is currently causing significant economic and environmental losses to fig tree nurseries and orchards in Central Italy. Fig damages are due to the adults feeding on leaves and fruits, and to the galleries dug by the xylophagous larvae in the trunk, which lead the plants to death. To date, no chemical or biological control methods resulted to be effective against this invasive pest. In order to gain information about possible semiochemicals involved in mate recognition and choice, both the volatile organic compounds (VOCs) and the epicuticular lipids of male and female specimens were analysed. VOCs emissions of specimens were characterized essentially by monoterpenes, while epicuticular lipids contained long chained 2-ketones, alkanes, alkenes, including some methyl alkenes, and several fatty acid propyl esters. The attractiveness of reconstituted VOCs blends of the two sexes was tested in electrophysiological and behavioural assays in laboratory conditions. Both the male and the female reconstituted VOCs drove a significant response towards individuals of the opposite sex, thus demonstrating features of sexual attractants. Our results suggest a possible application of VOCs blends as pheromonic attractants in field monitoring and mass trapping of Aclees sp. cf. foveatus.

Remarkable Reactions and Intermediates in Titanocene(IV) Chemistry: Migratory Insertion Reactions of 2,2-Disubstituted-1-alkenes, Intramolecular 1,5-σ Bond Metathesis via ε-Agostic Interactions, and a Rare Example of a β-Agostic Alkyltitanocene Complex

The compound Cp(2)TiMe(2) reacts with [Ph(3)C][B(C(6)F(5))(4)] in CD(2)Cl(2) at 205 K to give, inter alia, [Cp(2)TiMe(CD(2)Cl(2))][B(C(6)F(5))(4)]. This solvent-separated ion pair reacts in turn with 2,4-dimethyl-1-pentene (DMP) to give a series of cationic species, the first being the alkene complex [Cp(2)TiMe(DMP)](+), which undergoes ready migratory insertion to form the σ-alkyl complex [Cp(2)Ti(CH(2)CMe(2)CH(2)CHMe(2))](+). The latter, which does not contain a β-hydrogen atom, rearranges rapidly via an unprecedented 1,5-σ bond metathesis reaction involving two isomeric ε-agostic species to give the σ-alkyl species [Cp(2)Ti(CH(2)CHMeCH(2)CMe(3))](+); this does contain a β-hydrogen atom and, in concurrent processes, eliminates H(2) or 2,4,4-trimethyl-1-pentene (a major product) to form respectively the allylic complex [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CMe(3)}](+) (a major product) or the hydride complex [Cp(2)TiH](+). The latter reacts reversibly with free DMP to give the insertion product [Cp(2)Ti(CH(2)CHMeCH(2)CHMe(2))](+) (V, a major product), in which the italicized hydrogen atom engages in a β-agostic interaction with the metal atom. Compound V is a rare example of both a β-agostic derivative of a group 4 metallocene and a β-agostic compound of any metal in which the (1)H resonance of the agostic hydrogen can be identified in the (1)H NMR spectrum (δ -3.43). Interestingly, a NOESY experiment on V indicates slow mutual exchange between the agostic hydrogen atom, the hydrogen atoms on C(1), and those of Me(2). These observations are consistent with the intermediacy of the allylic dihydrogen species [Cp(2)Ti(H(2)){η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+), which loses H(2) to form [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+) (a minor product). Support for all steps of the proposed reaction scheme comes from product distributions, from labeling studies utilizing [Cp(2)Ti(CD(3))(CD(2)Cl(2))](+), and from extensive DFT calculations. The observed titanocene-based chemistry stands in stark contrast to that of the analogous zirconium system, in which the unusual but well-characterized cationic methyl alkene complex [Cp(2)ZrMe(DMP)](+) does not undergo migratory insertion and subsequent reactions.

ChemInform Abstract: A New Asymmetric Synthesis of (+)-Grandisol via a Kinetic Resolution.

Abstract A novel approach to the asymmetric synthesis of (+)-grandisol involves the use of catalytic kinetic resolution of a primary allylic alcohol. The allylic alcohol is prepared in 4 steps from simple achiral materials and the resolved alcohol (95%e.e.) is reduced in 2 steps to the corresponding methyl alkene. This alkene is converted to (+)-grandisol (95%e.e.).

An asymmetric synthesis of (+)-grandisol, a constituent of the aggregation pheromone of the cotton boll weevil, via a kinetic resolution.

A novel approach to the asymmetric synthesis of (+)-grandisol, (1R, 2S)-isopropenyl-1-methylcyclobutaneethanol, involves the use of catalytic kinetic resolution of a primary allylic alcohol, [(1RS, 5SR)-5-methylbicyclo[3.2.0]hept-2-en-2-yl] methanol. The allylic alcohol is prepared in four steps from simple achiral materials involving the use of a modified Shapiro reaction. The resolved alcohol (95% ee) is then reduced in two steps to the corresponding methyl alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene. This alkene is converted to (+)-grandisol (95% ee), in three steps, by modified literature procedures.

A new asymmetric synthesis of (+)-grandisol via a kinetic resolution

A novel approach to the asymmetric synthesis of (+)-grandisol involves the use of catalytic kinetic resolution of a primary allylic alcohol. The allylic alcohol is prepared in 4 steps from simple achiral materials and the resolved alcohol (95%e.e.) is reduced in 2 steps to the corresponding methyl alkene. This alkene is converted to (+)-grandisol (95%e.e.).

Enthalpies of hydrogenation of the octenes and the methylheptenes

Enthalpies of hydrogenation are given for the octenes and methylheptenes. Results follow the same general pattern that was found for alkenes and methyl alkenes of lower molar mass. Terminal double bonds not adjacent to a methyl group have ΔhydHom = −(125.6 ± 0.7) kJ·mol−1. Unbranched cis-octenes have ΔhydHom = −(118.5 ± 0.8) kJ·mol−1, and the trans-isomers have ΔhydHom = −(115.4 ± 0.4) kJ·mol−1. The terminal methyl, ethyl, or propyl groups of the trans-octenes stabilize the double bond about as much as the methyl group of 2-methylhept-1-ene: ΔhydHom = −(115.1 ± 0.7) kJ·mol−1.