3- Phenylpentane

Eriedel-Crafts alkylation of ben2ene with isomeric amyl alcohols proceeds with some rearrangement. Eor example, both 2- and 3-pentanol gave the identical product mixture (60% 2-phenylpentane, 31% 3-phenylpentane, and 9% / f/-pentylben2ene) from reaction with ben2ene in the presence of BE catalyst (85). 

Phenyl group, as hydrocarbon surface species, vibrational spectra, 42 228 Phenylindanyl cation NMR spectra, 42 146 Phenylnaphthalene, cyclization, 28 318 2-Phenylpentane cyclization, 28 299 isomerization, 30 67-68 reactions on different catalysts, 28 296,301 Phillips catalyst, 31 29... 

Better results were obtained for the carbamate of 163 (entry 3) [75, 80). Thus, deprotonation of the carbamate 163 with a lithium base, followed by complexation with copper iodide and treatment with one equivalent of an alkyllithium, provided exclusive y-alkylation. Double bond configuration was only partially maintained, however, giving 164 and 165 in a ratio of 89 11. The formation of both alkene isomers is explained in terms of two competing transition states 167 and 168 (Scheme 6.35). Minimization of allylic strain should to some extent favor transition state 167. Employing the enantiomerically enriched carbamate (R)-163 (82% ee) as the starting material, the proposed syn-attack of the organocopper nucleophile could then be as shown. Thus, after substitution and subsequent hydrogenation, R)-2-phenylpentane (169) was obtained in 64% ee [75]. 

The primary products of the cyclization of 2-phenylpentane are cis- and /ra j-l,3-dimethylindans, 1,3-dimethylindene, and 1-methylnaphthalene ... 

In the cases of -butylbenzene and 2-phenylpentane, there is an additional difference (other than ring size) between cyclization to naphthalenes and alkylindans. The reaction forming naphthalenes involves the addition of a primary carbon atom to the aromatic ring, while formation of alkylindans (and alkylindenes) involves secondary carbon atoms. With n-pentylbenzene, however, secondary carbon atoms are involved in both five- and six-ring cyclizations. 

First-order cyclization rate constants n-Butylbenzene n-Pentylbenzene 2-Phenylpentane... 

The methyl group in the y-position of the side-chain interferes with cyclization. The rate of C5-cyclization of n-butylbenzene at 371°C over platinum-on-silica gel is 3.5 times higher than that of 2-phenylpentane (Table IV) (14). The difference in C6-cyclization is even larger. Now, the side-chain carbon atoms involved in the cyclizations of n-butylbenzene and 2-phenylpentane have identical natures (i.e., secondary in five-membered ring closure and primary in six-membered ring closure). The difference between the two molecules (the extra methyl group) is far removed from the two carbon atoms involved in the formation of the new bond ... 

The stability of the intermediate carbonium ion determines whether cyclization forms five- or six-membered rings. In the case of n-butylbenzene and 2-phenylpentane, acid-catalyzed six-ring cyclization would involve very unstable primary carbonium ions C6H5-CH2-CH2-CH2-CH2+ or C6H5-CH(CH3)-CH2-CH2-CH2 +. Therefore, only five-membered rings could be formed in acid-catalyzed cyclization from these two hydrocarbons. 

About half of the 1-methylnaphthalene formed from n-pentylbenzene and 2-phenylpentane isomerizes to 2-methylnaphthalene over platinum on silica-alumina (while over platinum on silica less than 3% of the methylnaphthalene isomerizes to 2-methylnaphthalene). Alkylindan (and alkyl-indene) isomerization is also considerable over platinum on silica-alumina (13, 14). 

One of the most direct ways to produce diastereomers is by addition reactions across carbon-carbon double bonds. If the structure of the olefin substrate is such that two new chiral centers are produced by the addition of a particular reagent across the double bond, then diastereomers will result. For example, the addition of HBr to Z-3-chloro-2-phenyl-2-pentene produces 2-bromo-3-chloro-2-phenylpentane as a mixture of four diastereomers. Assuming only Markovnikov addition, the diastereomers are produced by the addition of a proton to C-3 followed by addition of bromide to the carbocation intermediate at C-2. Since the olefin precursor is planar, the proton can add from either face, and since the carbocation intermediate is also planar and freely rotating, the bromide can add to either face to give diastereomeric products. The possibilities are delineated schematically (but not mechanistically) below. 

In the case of n-pentylbenzene and 2-phenylpentane (759), the same types of isomerization, via bond shift and cyclic mechanisms, proceed, but the situation seems complicated by consecutive reactions occurring without... 

Nomenclature Using Benzene as a Prefix Section 6.3F (a) 2,4-dimethyl-2-phenylpentane (b) p-benzylbenzaldehyde ... 

Fig. 2.30. Active site model of PPL showing the binding of 2-phenylpentane-l,4—diol in an active site. Note the it —tt-stacking with Phe-216 and placement of the C(4) hydroxyl near the acyl serine-153 residue. Reproduced from Tetrahedron, 55, 14961 (1999), by permission of Elsevier. (See also color insert.)...

Cram and Dalton (//) have observed that reaction of t/ireo-2-phenyl-3-pentyl methanesulfonate (33) with potassium in 1,2-dimethoxyethane gave a hydrocarbon product containing 94% of 2-phenylpentane and 6% of 3-phenylpentane (product of phenyl migration). 

Similarly, treatment of t/ireo-3-phenyl-2-pentyl methanesulfonate with sodium in liquid ammonia gave hydrocarbon products containing 3% of 2-phenylpentane (product of phenyl migration). Treatment of 1,1-dideu-terio-l-methoxy-2-(l-naphthyl)ethane (34a) or l,l-dideuterio-2-(l-naph-thyl)ethyl methanesulfonate (34b) with potassium in 1,2-dimethoxy-... 

Phenylpentanoic acid, A49.9, A"46 Pyrethrolone, T17.4 Isopyrethrolone, T17.2 2-Hydroxy-2-phenylpentan-3-one, A51.5 9-Methyl-A -octalin-l,6-dione, A 38.10 2-Ethyl-3-phenylpropionic acid, A"48.17 Homoadamantane-2,7-dione, X"10.8... 

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