L,4-Pentadien

The (partial) description of the synthesis and coupling of the five fragments starts with the cyclohexyl moiety C —C. The first step involved the enantio- and diastereoselective harpless epoxidation of l,4-pentadien-3-ol described on p. 126f. The epoxide was converted in four steps to a d-vinyl d-lactone which gave a 3-cyclohexenecarboxylate via Ireland-CIaisen rearrangement (cf. p. 87). Uncatalysed hydroboration and oxidation (cf. p. 131) yielded the desired trans-2-methoxycyclohexanol which was protected as a silyl ether. The methyl car-... 

The reaction of allyl halides with terminal alkynes by use of PdClifFhCNji as a catalyst affords the l-halo-l,4-pentadienes 297. 7r-AlIylpalladium is not an intermediate in this reaction. The reaction proceeds by chloropalladation of the triple bond by PdCh, followed by the insertion of the double bond of the allyl halide to generate 296. The last step is the regeneration by elimination of PdCh, which recycles[148]. The cis addition of allyl chloride to alkynes is supported by formation of the cyclopentenone 299 from the addition product 298 by Ni(CO)4-catalyzed carbonylation[149]. 

The di-7r-methane rearrangement has been studied in a sufficient number of cases to develop some of the patterns regarding substituent effects. When the central sf carbon is unsubstituted, the di-7i-methane mechanism becomes less favorable. The case of 1,1,5,5-tetraphenyl-l,4-pentadiene is illustrative. Although one of the products has the expected structure for a product of the di-7t-methane rearrangement, labeling with deuterium proves that an alternative mechanism operates ... 

When Talkoxy-l,4-pentadienes are used Instead of 2-alkoxy-l,4-pentadienes, tandem Inter [4- 2 /lntra [3- 2 cycloaddidon of nitroalkenes followed by hydrogenolysls affords a versatile asymmetric synthesis of highly fiincdonalized aminocyclopentanes fScheme 8.47i. ... 

Ebenfalls iiber einen Dreiring (Bis-[benzyliden]-cyclopropanon) verlauft die Reduktion von 2,4-Dibrom-3-oxo-l,5-diphenyl-l,4-pentadien in DMF [isoliert wild3-Oxo- 1,5-di-phenyl-penten-(4)-in-( 1)]. In Methanol hingegen bildet sich 5-Oxo-2,3-diphenyl-cydo-penten3. 

Spirodibenzopyrans are prepared by two principal routes (A) condensation of two equivalents of salicylaldehyde with appropriate ketone (B) condensation of o-hydroxystyryl ketone 15, which is prepared from salicylaldehyde and a ketone in the presence of KOH, with the same or different salicylaldehyde derivatives, as shown in Scheme 10.2,48 Spirodibenzopyran can also be obtained from l,5-bis(2-hydroxyphenyl)-l,4-pentadiene 16 by dehydrogenative reaction (C).48... 

The photochemistry of l,l,5,5-tetraphenyl-3,3-dimethyl-l,4 pentadiene (1) has been studied in detail by Zimmerman and Mariano.<7) Photolysis of compound (1) gave 1,1-diphenyl-2,2-dimethyl-3-(2,2-diphenylvinyl) cyclopropane ... 

Isomerization versus Reduction Reaction Pathways in the Hydrogenation of 3-Buten-2-ol and l,4-Pentadien-3-ol on Pd-Black... 

The general experimental procedure employed in the study here has been described previously (7), thus only a brief overview is presented here. For all experiments, 45 mL deionized water and catalyst (50 mg Pd-black for 3-buten-2-ol and 25 mg for l,4-pentadien-3-ol) were added to the reaction cell. For ultrasound-assisted, as well as stirred (blank) experiments, the catalyst was reduced with hydrogen (6.8 atm) in water for 5 minutes at an average power of 360 W (electrical 90% amplitude). The reagents (320 mg 3-buten-2-ol or 360 mg l,4-pentadien-3-ol) were added to the reduced catalyst solution to achieve... 

Figure 2 Time-dependent composition data is shown for the hydrogenation of aqueous l,4-pentadien-3-ol for both (a) ultrasound irradiated and (b) magnetically stirred systems. The symbols correspond to experimental measurements (l,4-pentadien-3-ol 14PD30L-solid circles l-penten-3-ol lP30L-open hourglass 3-pentanone 3PONE-open triangles 3-pentanol 3POL-crossed squares). The lines in the ultrasound experiment simply connect the data points, whereas for the stirred experiment the lines correspond to a modeled fit (see text).

Something that will become useful are the hydrogenation reaction schemes for 3-buten-2-ol and l,4-pentadien-3-ol are illustrated below. 

The third member of the tandem inter [4+2]/intra [3+2] cycloaddition family is classified as the bridge mode, in which the dipolarophile is attached to the dienophile. Simple, 1,4-pentadi-enes as well as 2-alkoxy-l,4-pentadienes can function effectively as dienophiles and dipolarophile combinations with excellent chemical selectivity and regio- and diastereoselectivity. Hydrogenation of the bridged nitroso acetals produces hydroxymethylated derivatives in high diastereo- and enantioselectivity (Eq. 8.116).185... 

Lipoxygenases, which catalyse the oxidation of unsaturated fatty acids containing the cis,cis-l,4-pentadiene moiety to the corresponding 1 -hydroperoxy-f rans,ds-2,4-diene (Table 2.3), are widely distributed in plants and animals. The mammalian... 

The biosynthetic origin of the depolymerization-resistant core of cutin (cutan) remains to be established. The early observation that linoleic acid and linolenic acid were preferentially incorporated into the non-depolymerizable core of cutin in apple skin slices suggested that the ether-linked or C-C-linked core might arise preferentially from the czs-l,4-pentadiene system [31]. The insoluble residue, that contained the label from the incorporated polyunsaturated C18 acids, released the label upon treatment with HI, supporting the notion that some of those aliphatic chains were held together by ether bonds. More recently,... 

The isomer distributions were measured at <25% butadiene conversion. T 1C = trans/ cis ratio of 1,4-hexadiene 3-MeP=3-methyl-l,4-pentadiene. 

Perfluoro-l,4-pentadiene and perfluoropropene undergo similar reactions. Atkinson and McKeagen 41 reported two similar reactions ... 

C17H15NO 1,5-diphenyl-l,4-pentadien-3-one oxime Extraction-photometric Cu 61... 

Die mit Palladium-Komplexen wie Bis-[l,5-diphenyl-3-oxo-l,4-pentadien]- und Bis-[1,2-bis-(diphenyl-phosphano)-ethan]-pa ladium(0)2 katalysierte Addition von Allylestern an Imine aus Glycin bzw. Alanin-estem sowie Benzophenon bzw. (4-Chlor)Benzaldehyd kann zur Synthese von Derivaten hoherer und auch funktionalisierter, y, -ungesattigter a-Ami-no-carbonsauren verwendet werden3,4. Im einfachsten fuhrt dies zu solchen der 2-Amino-4-pentensaure. 

Reaction of 3,3-disubstituted-l,4-pentadiene 92 with a primary amine under cyclohydrocarbonylation conditions yielded cyclopenta[. ]pyrrole 96 as the predominant product accompanied by a small amount of cyclopentanone 95 (Scheme 15). This unique reaction is proposed to proceed through a cascade hydrocarbonylation-carbonylation process. The first hydrocarbonylation of 92 and the subsequent carbocyclization formed cyclopentanoylmethyl-Rh complex 93. If 93 immediately reacts with molecular hydrogen, 2-methylcyclopentanone 95 is formed. However, if CO insertion takes place faster than the hydrogenolysis, cyclopentanoylacetyl-Rh complex 94 is generated, which undergoes the Paal-Knorr condensation with a primary amine to yield cyclopenta[. ]pyrrole 96. ... 

The volatiles produced by the LOX pathway and autoxidation are typically volatile aldehydes and alcohols responsible for fresh and green sensorial notes. In the LOX pathway these volatile compounds are produced in response to stress, during ripening or after damage of the plant tissue. The pathway is illustrated in Scheme 7.2. Precursors of the LOX (EC 1.13.11.12) catalysed reactions are Cis-polyunsaturated fatty acids with a (Z,Z)-l,4-pentadiene moiety such as linoleic and a-linolenic acids that are typically oxidised into 9-, 10- or 13-hydro-peroxides depending on the specificity of the LOX catalyst. These compounds are then cleaved by hydroperoxide lyase (HPL) into mainly C, C9 and Cio aldehydes, which can then be reduced into the corresponding alcohols by alcohol dehydrogenase (ADH EC 1.1.1.1) (Scheme 7.2) [21, 22]. The production of volatile compounds by the LOX pathway depends, however, on the plants as they have different sets of enzymes, pH in the cells, fatty acid composition of cell walls, etc. 

Lipoxygenase (EC 1.13.11.12) is an enzyme that catalyzes the hydroperoxidation of polyunsaturated fatty acids and esters containing a cis-cis-l, 4-pentadiene system (Table 6). In 1947, Theorell et al. obtained the enzyme in a crystalline form from soybeans and reported that the enzyme neither contained nor required a metal cofactor192. Subsequent studies from three groups of investigators have demonstrated that the enzyme purified from soybeans in an iron-containing dioxygenase74-76 ... 

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