3-Phenylpropene, hydrogenation

A significant modification in the stereochemistry is observed when the double bond is conjugated with a group that can stabilize a carbocation intermediate. Most of the specific cases involve an aryl substituent. Examples of alkenes that give primarily syn addition are Z- and -l-phenylpropene, Z- and - -<-butylstyrene, l-phenyl-4-/-butylcyclohex-ene, and indene. The mechanism proposed for these additions features an ion pair as the key intermediate. Because of the greater stability of the carbocations in these molecules, concerted attack by halide ion is not required for complete carbon-hydrogen bond formation. If the ion pair formed by alkene protonation collapses to product faster than reorientation takes place, the result will be syn addition, since the proton and halide ion are initially on the same side of the molecule. 

Reaction of AT-fluorobis(trifluoromethylsulfonyl)amine (Id) with alkenes gives various products, depending on the reaction conditions and the structure of the substrate. In solvents of higher nucleophilicity such as water, acetic acid, aqueous hydrochloric acid, and 70 % hydrogen fluoride/pyridine, a-fluorohydrins or their acetates, a-chloro-fl-fluoroalkanes or a,/ -difluoroal-kanes, e.g. 14. are obtained.146 Reaction of styrene and ( >l-phenylpropene with Id in dich-loromethane/acetic acid gives l-acetoxy-2-fluoro-l-phenylethane and -propane, in 92 and 99 % yield, respectively, the latter product in a ratio (erythrojthreo) 1 l.146... 

IEs were used to verify a tautomeric equilibrium in 2-phenylpropenal-c/ (47 + 48) and to distinguish this mixture from a symmetric structure with a hydrogen centered within the hydrogen bond.120 According to 13C and H chemical shifts, the equilibrium favors 48. From the temperature dependence AH° was estimated as -27 cm-1, or -0.08 kcal mol-1. Because both tautomers have the same conjugate base, 47, which is less stable, must be the stronger acid, owing to a secondary deuterium IE. 

This is not the precise value for the hydrogenation enthalpy as reported by Abboud and coworkers94, 105.9 1.2 kJmol-1, but, as indicated above in the text, a composite value was used to generate the enthalpy of formation of the unsaturated hydrocarbon. As such, the hydrogenation enthalpy employed here was the difference of the suggested enthalpy of formation of ( )-l-phenylpropene from this source and the archival value for propylbenzene. 

Phenylpropenal reacted with ethylamine in the presence hydrogen and Pt as catalyst and BaS04 and N-ethyl-3,3 -diphenyldipropylamine (alverine) was obtained. 

Cabaleiro and Johnson (1967) report that the addition of chlorine to -methyl cinnamate in chloroform or acetic acid is syn-selective, SS 0-75, in chloroform and acetic acid acetoxychloro derivatives are produced as well. Again, Dewar and Fahey (1964) argue that the normal course of addition of hydrogen halides onto olefins is a polar electrophilic process involving classical carbonium ions as intermediates and leading mostly but not exclusively to cis-adducts. A syn-preference was found in the additions of deuterium bromide to acenaphthylene, indene, and cis- and fraws-phenylpropene. In the case of indene, phenylpropene and methyl cinnamate, which are styrene analogs, concerted syn addition is symmetry-allowed (see bottom of p. 273). 

When allylic hydrogens are present in the alkene, A-allyl hydrazine derivatives are formed preferentially by the ene reaction (Section 7.6.). Furthermore, the reaction of styrenes, (Ey -phenylpropene, and stilbenes with diazenedicarboxylates (traditionally known as azodicar-boxylates) and triazolediones affords products involving double Diels-Alder or Diels-Alder-ene reactions (Section 7.2.10.3.3.). 

Chloro-l-phenylpropene (cinnamyl chloride) was reductively dehalogenated in water/n-heptane biphasic systems by hydrogen transfer from formates using Pd(II) complexes with sulfonated phosphine ligands of the type 21 (Scheme 3.38) [271], Addition of polyether detergents increased the rate of hydrogenolysis and supressed the formation of alcohol... 

Hydrogen-abstraction Reactions.—The main product from the irradiation of the ene-ol (6) in hexane or benzene is the tetrahydrofuran (7).B This arises from the singlet state of the olefin, probably by intramolecular protonation and cycliza-tion. In benzene the tetrahydrofuran is accompanied by 2-phenylpropene and acetophenone. These products arise from the triplet state (their formation is suppressed by the addition of cyclohexa-1,3-diene as quencher). The mechanism for the formation of the fission products is shown in Scheme 2 and is analogous... 

Hydrogenation of linear alkenes such as 2-pentene, 2-octene, and 1-phenylpropene... 

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