565-78-6Relevant academic research and scientific papers
On rearrangements by cyclialkylations of arylpentanols to 2,3-dihydro-1H-indene derivatives. Part 5. The acid-catalyzed cyclialkylation of 2-(2-chlorophenyl)-2,4-dimethylpentan-3-ol
Fathi, Behrouz,Giovannini, Edgardo,Pasquier, Pierre
, p. 2089 - 2104 (2007/10/03)
The mechanism proposed in [1] to explain the surprising result of the cyclialkylation of 4-(2-chlorophenyl)- 2,4-dimethylpentan-2-ol (3, R = Me), which gives not only the 'normal' product, i.e., the 4-chloro-2,3-dihydro-1,1,3,3-tetramethyl- (4), but also the isomer trans-4-chloro-2,3-dihydro-1,1,2,3-tetramethyl-1H-inden (5), could be differentiated in two sections (cf. Scheme 2): the first from 3 to the intermediary ion IIa?IIb, and the second from the latter ions to the final product 5. For the first section, a sufficiently satisfactory explanation has been given in [1]; the second section has received important support from the mechanisms of the cyclialkylation of 2,4-dimethyl-2-phenylpentan-3-ol (6), the precursor of II′a, the ion IIa without the o-Cl substituent (cf. Schemes 2, 3 and 5 and [4]). The present communication gives an explanation of the influence of the o-Cl substituent: a mechanism is proposed for the very complex cyclialkylation of 2-(2-chlorophenyl)-2,4-dimethylpentan-3-ol (11; cf. Scheme 9). Both mechanism may be considered as definitive. It is very surprising that, by the cyclialkylation of the compounds 1, 3, 8, 11, 15, and 17, only compound 1 gives the 'normal' product: the cyclialkylation of all other phenylpentanols follows complex pathways including Et, i-Pr, and Ph migrations, which could not be expected. In addition, it has been established that the transformation of 21 to 22 (cf. Scheme 12) and that of 23 to 24 (cf. Scheme 13) occur through two consecutive 1,2- and not through a single 1,3-hydride migration or through an elimination-addition process (cf. Scheme 13). It can be assumed that the transformation of ion IV (the 2-(2-chlorophenyl)-3,4-dimethylpent-2-ylium ion) to the ion V (the 4-(2-chlorophenyl)-3,4-dimethylpent-2-ylium ion (both shown in Scheme 9 as D-isomers) occurs through the same pathway.
The Diastereoselectivity of Electrophilic Attack on Trigonal Carbon Adjacent to a Stereogenic Centre: Diastereoselective Alkylation and Protonation of Open-chain Enolates having a Stereogenic Centre at the β Position
Fleming, Ian,Lewis, Jeremy J.
, p. 3257 - 3266 (2007/10/02)
Methylation of the enolates 7, 24, 28 and 33 and protonation of the enolates 10, 27, 31 and 36 are diastereoselective in conformity to a general rule, summarised in the drawing 1, governing the stereochemistry of electrophilic attack on a double bond adjacent to a stereogenic centre.The sense of the selectivity is, with one exception, opposite to that of the corresponding nucleophilic attack on a carbonyl group adjacent to a stereogenic centre, which, with the same exception, follows Cram's and the Felkin-Anh rule, summarised in the drawing 2.The exception is probably the reduction 40 -> 38 + 39, with 39 as the major product.This result is inconsistent with Cram's and the Felkin-Anh rule if the isopropyl group is counted as 'larger' than the phenyl group, whereas the Grignard reaction 37 -> 38 + 39, where 39 is again the major product, and the corresponding electrophilic reactions 33 -> 34 + 35, with 34 as the major product, and 36 -> 34 + 35, with 35 as the major product, are all consistent with isopropyl being effectively larger than phenyl.
Charge-reversal Mass Spectra of Enolate Ions of Some Open-chain and Cyclic Ketones for Structure Identification
Suerig, Thomas,Gruetzmacher, Hans-Friedrich
, p. 446 - 452 (2007/10/02)
The charge-reversal (CR) mass spectra of the enolate ions of heptanal and ten isomeric heptanones, of cyclohexanone, of cycloheptanone, of isomeric methylcyclohexanones, of isomeric ethylcyclohexanones and of the isomeric monoterpene ketones camphor, fenchone, pulegone and thujone were obtained by deprotonating using OH(-) under chemical ionization conditions followed by collision of the (-) ions with helium in the second field-free region of a VG ZAB 2F mass spectrometer.The CR mass spectra were evaluated by similarity index (SI) values.Characteristic of the CR mass spectra of the open-chain enolates are fragment ions formed by α- cleavage.However, the CR mass spectra are dominated by peaks of small hydrocarbon ions, particularly in the case of cyclic and bicyclic enolates.The CR mass spectra of enolates of linear heptanones differing in the position of the carbonyl group can be easily correlated with the structure of the parent ketone.The CR mass spectra of enolates of isomeric heptan-2-ones differing only in the degree of branching of the alkyl group are similar, but can be distinguished by the SI values.The CR mass spectra of the enolates of the isomeric cyclic and bicyclic ketones studied are more or less identical and cannot be used for structural assignment.
Lewis Acid-prompted Conjugate Reduction of α,β-Unsaturated Carbonyl Compounds by 2-Phenylbenzothiazoline (2-Phenyl-2,3-dihydrobenzothiazole)
Chikashita, Hidenori,Miyazaki, Makoto,Itoh, Kazuyoshi
, p. 699 - 706 (2007/10/02)
Reduction of various α,β-unsaturated ketones (3a-g) and (4a-d) in methanol by the benzothiazoline (1) in the presence of aluminium chloride gives, in all cases, the corresponding saturated ketones (5a-g) and (6a-d)without any of the unsaturated or saturated alcohol.Reduction of α,β-unsaturated esters (7a,b) similarly gives the saturated esters (9a,b), while reaction of cinnamaldehyde (8) with compound (1) does not occur at all.Among the Lewis acids examined, aluminium chloride gives the best results.Reduction of 2'-azachalcone (21) with 2-phenylbenzothiazoline reveals that, in the reduction product, the deuterium atom is located at the β-position with respect to the carbonyl group.The result obtained from the reduction of the same substrate with compound (1) in methanol shows that no incorporation of a hydrogen atom from the solvent takes place and suggests (indirectly) that the introduced hydrogen atom at the α-position of the product comes from the benzothiazoline (1).The reaction of (Z)-1,2-dibenzoyl-1,2-diphenylethylene (30) with compound (1) in the presence of aluminium chloride stereospecifically yields meso-1,2-dibenzoyl-1,2-diphenylethane (31).This shows that the transfer of two hydrogens from compound (1) to the carbon-carbon double bond of the enone proceeds via cis-addition.Experiments with ethyl phenylpropiolate (28) also support cis-reduction for the present conjugate reduction.These results are interpreted in terms of a mechanism involving synchronous transport of a pair of hydrogens from the benzothiazoline (1); i.e a cyclic addition of the two hydrogens either in exact or nearly exact concurrence.
