Pentanes, alkyl-substituted—

Lipid-Protein-Carbohydrate Interactions. Evidence for such complex interaction was recently reported by Huang et al (36) who observed that the addition of corn lipids to zein and corn carbohydrates enhanced the formation of alkylpyrazines, indicating that lipid-derived free radicals may accelerate the rate of Maillard reactions. Two of the alkylpyrazines, identified in such mixtures after heating for 30 minutes at 180°C, have 5-carbon alkyl substitution at the pyrazine ring and could only be explained by interaction of lipid or lipid decomposition products. These authors suggested that condensation of amino ketones, formed by protein-carbohydrate interaction, may yield 3,6-dihydropyrazine which would in turn react with pentanal, a lipid oxidation product, to form 2,5-dimethyl-3-pentylpyrazine. 

Alkyl substituted dinitropentanes. There are two such compds of interest 1,2-Dinitro-2-Methyl-Propane. See Vol 5, D1391-R and Vol 2, B368-R where it is described as Dinitro-iso-butane The Sodium salt of 1,1-Dinitro-2-Methoxy-Pentane. CH3.CH2.CH2.CH(OCH3).C.(Na)(N02)2, mw 142.15, yel ndls, mp, explds. Prepn is by slow (drop by drop) addn of Na methyl alco-... 

All these results are readily interpreted by assuming the existence of two bond shift mechanisms. The first one, which accounts for methyl shift, may be ascribed to the metallocyclobutane mechanism responsible for the group III reactions of n-pentane and isopentane. The second one, which accounts for chain lengthening (and chain shortening) is the same as the mechanism of higher activation energy (group II) responsible for the interconversion between n-pentane and isopentane. The first is very sensitive to alkyl substitution, while the latter seems relatively insensitive to structural effects. 

The differences in the activation energies are due both to the strain energy of the cyc/o-pentane ring and to the presence of methyl and alkyl substitutions on the ring. 

The oligomerization of propene on zeolite H-Y has been studied [33,37] by variable-temperature MAS NMR. Alkoxy species formed between protonated alkenes and oxygens of the zeolitic framework were found to be important long-lived intermediates in these reactions. Simple secondary or tertiary carbocations are either absent in the zeolite at low temperatures, or are so transient as to be undetectable by NMR even at temperatures as low as 163 K. There was, however, evidence for long-lived alkyl-substituted cyclopentenyl carbocations, which are formed as free ions in the zeolite at room temperature. At 503 K the oligomers crack to form branched butanes, pentanes and other alkanes. The final product was highly aromatic coke. The structure, dynamics and reactivity of an alkoxy intermediate formed from acetylene on zeolite catalysts have been investigated by Lazo et. al. [32]. 

In another report using isolated CRED enzymes, Kalaitzakis et al. demonstrated that alkyl-substituted 1,3-diketones 67 of the type in Scheme 6.26 could be reduced with high diastereoselectivities. By screening libraries of CREDs, enzymes capable of producing two or three of the four possible diastereomers were often found. An interesting case was the reduction of compounds such as 3-met hyl-3-allyl-2,4-pentanedione (Scheme 6.26) that gave only a single product in 100% yield. The chiral alcohol was identified as (3R,4R)- 3-methyl-3-allyl-4-hydroxy-pentan-2-one Other similar examples of this type of reaction were also described [40]. 

Gleiter et aL found that the alkyl-substituted g -tricyclo[4.2.0.0 - ]octa-3,7-dienes 33, 36,41, and 43 afforded the cubane derivatives 34, 37,42, and 44 via photoirradiation (high-pressure Hg lamp) of the pentane solution. In the case of octamethyl-diene 36, six different photoproducts were isolated, but the main product was octamethylcuneane 38. The cubane 37 may be formed directly via photoirradiation, whereas a mechanism involving either a biradical intermediate or the triene 40 was proposed for the formation of other products (38, 39). Although the parent 28 is photochemically inactive, Gleiter et al. revealed that its octaalkyl derivatives have a rich photochemistry. 

A class of enzymes capable of removing sulfur from alkane sulfonates exists, which may have relevance in microbial desulfurization of alkyl sulfides. A gene cluster ssuEADCB was identified in E. coli. The enzyme SsuD was capable of conversion of pentane sulfonic acid to pentaldehyde and sulfite. It was reported to be capable of conversion of alkyl sulfonates from C2 to CIO, as well as substituted ethanesulfonates and sulfonated buffers. The SsuE was a flavin-reducing enzyme that provided FMNH2 to the SsuD. 

Seebach and Naef1961 generated chiral enolates with asymmetric induction from a-heterosubstituted carboxylic acids. Reactions of these enolates with alkyl halides were found to be highly diastereoselective. Thus, the overall enantioselective a-alkyla-tion of chiral, non-racemic a-heterosubstituted carboxylic acids was realized. No external chiral auxiliary was necessary in order to produce the a-alkylated target molecules. Thus, (S)-proline was refluxed in a pentane solution of pivalaldehyde in the presence of an acid catalyst, with azeotropic removal of water. (197) was isolated as a single diastereomer by distillation. The enolate generated from (197) was allylated and produced (198) with ad.s. value >98 %. The substitution (197) ->(198) probably takes place with retention of configuration 196>. 

---