Crotonyl

Crotonyl isothiocyanate, C4H7. N C S, has been found in Indian rape-seed oil. It is an oil of odour somewhat similar to that of the corresponding allyl compound, and having the following characters —... 

Mephenesin Crotonaldehyde Tilidine HCl Crotonyl chloride Crotamiton Cupric acetate... 

In biological pathways, dehydrations rarely occur with isolated alcohols but instead normally take place on substrates in which the -OH is positioned two carbons away from a carbonyl group. In the biosynthesis of fats, for instance, /3-hydroxybutyry) ACP is converted by dehydration to tram-crotonyl ACP, where ACP is an abbreviation for acyl carrier protein. We ll see the reason for this requirement in Section 11.10. 

One of the steps in fatty-acid biosynthesis is the dehydration of (i )-3-hydroxy-butyryl ACP to give frans-crotonyl ACP. Does the reaction remove the pro-JR or the pro-5 hydrogen from C2 ... 

All three elimination reactions--E2, El, and ElcB—occur in biological pathways, but the ElcB mechanism is particularly common. The substrate is usually an alcohol, and the H atom removed is usually adjacent to a carbonyl group, just as in laboratory reactions. Thus, 3-hydroxy carbonyl compounds are frequently converted to unsaturated carbonyl compounds by elimination reactions. A typical example occurs during the biosynthesis of fats when a 3-hydroxybutyryl thioester is dehydrated to the corresponding unsaturated (crotonyl) thioester. The base in this reaction is a histidine amino acid in the enzyme, and loss of the OH group is assisted by simultaneous protonation. 

Subsequent dehydration of /3-hydroxybutyryl ACP by an ElcB reaction in step 7 yields trans-ciotonyl ACP, and the carbon-carbon double bond of crotonyl ACP is reduced by NADPH in step 8 to yield butyryl ACP. The doublebond reduction occurs by conjugate addition of a hydride ion from NADPH to the /S carbon of fraus-crotonyl ACP. In vertebrates, the reduction occurs by an overall syn addition, but other organisms carry out similar chemistry with different stereochemistry. 

Problem 29.4 Write a mechanism for the dehydration reaction of /3-hydroxybutyryl ACP to yield crotonyl ACP in step 7 of fatty-acid synthesis. 

In step 7 of fatty-acid biosynthesis (Figure 29.5), dehydration of a /3-hydroxy thioester occurs to give fm/rs-crotonyl ACP. Is the dehydration a syn elimination or an anti elimination ... 

Lewis-acid-catalyzed asymmetric hetero-Diels-Alder cycloaddition of a 1-thiabuta-1,3-diene with chiral A/-acryloyl and A/-crotonyl oxazolidinone dienophile [105]... 

Zeijden [112] used chiral M-functionalized cyclopentadiene ligands to prepare a series of transition metal complexes. The zirconium derivative (82 in Scheme 46), as a moderate Lewis acid, catalyzed the Diels-Alder reaction between methacroleine and cyclopentadiene, with 72% de but no measurable enantiomeric excess. Nakagawa [113] reported l,T-(2,2 -bis-acylamino)binaphthalene (83 in Scheme 46) to be effective in the ytterbium-catalyzed asymmetric Diels-Alder reaction between cyclopentadiene and crotonyl-l,3-oxazolidin-2-one. The adduct was obtained with high yield and enantioselectivity (97% yield, endo/exo = 91/9, > 98% ee for the endo adduct). The addition of diisopropylethylamine was necessary to afford high enantioselectivities, since without this additive, the product was essentially... 

The degradation of pimelate is initiated by formation of the coenzyme A ester and is followed by a series of steps with the production of glutaryl-CoA that is decarboxylated to crotonyl-CoA... 

Scheme 2.92. Three-component asymmetric synthesis of 3-alkyl-4-methoxycarbonyl-azetidin-2-ones 2-386 from chiral crotonyl derivatives.

The reaction is catalyzed by the fifth synthetase enzyme-hydroxy acyl hydratase, to produce crotonyl. 

Asymmetric Michael addition of nitromethane to a crotonyl camphorsultam gives access to the enantio-pure 2-oxoesters, which may be converted into the 3-hydroxy-5-methylpiperidin-... 

The kind of enantiomer [d-(-)- or l-(+)-] synthesized in the formation of the C4 intermediate varies. The acetoacetyl-CoA reductase (EC 1.1.1.36), which is NADPH-dependent, stereoselectively reduces acetoacetyl-CoA to d-(-)-3-hydroxybutyryl-CoA (R. eutropha [15]). The NADH-dependent reductase catalyzes the reduction of acetoacetyl-CoA to L-(+)-3-hydroxybutyryl-CoA. Afterwards two stereospecific crotonyl-CoA hydratases, l-(+)- and D-(-)-speci-fic, convert the L-(+)-3-hydroxybutyryl-CoA into the D-(-)-isomer (Rhodo-spirillum rubrum [16]). 

In Aeromonas caviae, 3-ketothiolase and acetoacetyl-CoA reductase are absent. In this species, the synthesis of poly(3HB) proceeds via an enoyl-CoA hy-dratase from either crotonyl-CoA or hexenoyl-CoA. The enoyl-CoA derivatives stem from the fatty-acid oxidation pathway [18]. 

Crotononitrile, b482 trans-Crotonyl alcohol, c311 Crotyl alcohols, b486, b487 Crotyl bromide, b276 Crotyl chloride, c79... 

The first organoaluminium complex that catalysed a Diels Alder reaction was formed from menthol and ethylaluminium dichloride. This finding was complemented by work of Corey who showed that the aluminium diamine complex (49) was effective for controlling the stereochemistry of Diels-Alder reactions involving cyclopentadiene and acryloyl and crotonyl amides (e.g. 

Asymmetric Diels-Alder reactions. Unlike methyl crotonate, which is a weak dienophile, chiral (E)-crotonyl oxazolidinones when activated by a dialkylaluminum chloride (1 equiv.) are highly reactive and diastereoselective dienophiles. For this purpose, the unsaturated imides formed from oxazolidinones (Xp) derived from (S)-phenylalanol show consistently higher diastereoselectivity than those derived from (S)-valinol or (IS, 2R)-norephedrine. The effect of the phenyl group is attributed in part at least to an electronic interaction of the aromatic ring. The reactions of the unsaturated imide 1 shown in equation (I) are typical of reactions of unsaturated N-acyloxazolidinones with cyclic and acyclic dienes. All the Diels-Alder reactions show almost complete endo-selectivity and high diastereoselectivity. Oxazolidinones are useful chiral auxiliaries for intramolecular Diels-Alder... 

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