F Crotonaldehyde

Cinnamaldehyde, 3134 f Crotonaldehyde, 1516 f Cyclopropyl methyl ether, 1608 f Diallyl ether, 2431... 

Coloma F, Sepulveda-Escribano A, Fierro JLG, Rodrfguez-Reinoso F. Crotonaldehyde hydrogenation over bimetallic Pt-Sn catalysts on pre-graphitized carbon black. Effect of the Sn/Pt atomic ratio. Appl CatalA Gen 1996 136 231-248. 

Figure 6.15 The infrared vibrational spectrum of crotonaldehyde. The parts marked (a), (b) and (c) refer to a 10 per cent (by volume) solution in CCI4, a 1 per cent solution in CCI4, and a thin liquid film, respectively. [Reproduced, with permission, from Bowles, A. J., George, W. O. and Maddams, W. F J. Chem. Soc. (B), 810, 1969]...

Figure 6.17 The laser Raman vibrational spectmm of liquid crotonaldehyde. [Reproduced, with permission, from Durig, J. R., Brown, S. C., Kalasinsky, V F. and George, W. O., Spectrochim. Acta, 32A, 807, 1976. Copyright 1976 Pergamon Press]...

Fig. 9. Dependence of relative molar concentrations Wj/nA0 of reaction components on reciprocal space velocity W/F (hr kg mole 1) in the parallel-consecutive hydrogenation of crotonaldehyde. Temperature 160°C, catalyst Pt-Fe/Si02 (1% wt. Pt, 0.7% Fe), initial molar ratio of reactants G = 10. The curves were calculated (1—crotonaldehyde, 2—butyraldehyde, 3—crotyl alcohol, 4—butanol) the points are experimental values.

This conjugated enone/diene difference is more definitively seen in the 184 kJ mol-1 decrease in enthalpy of formation on going from 1-pentene to butanal, in contrast to the 177 kJ mol-1 going from (E)-l,3-pentadiene to irans -crotonaldehyde. For further discussion, see J. F. Liebman and R. M. Pollack, in The Chemistry ofEnones (Eds. S. Patai and Z. Rappoport), Wiley, Chichester,... 

When the second component is an a,/i-unsaturated aldehyde, somewhat different results are reported. Thus crotonaldehyde reacts with ethyl aceto-acetate to give 4/f-pyran 65,86 whereas 3-substituted crotonaldehydes with 1,3-cyclohexadiones afford 67 to 80% of the corresponding 2//-pyrans 66. ° The reaction with 1,3-pentanedione proceeded also in the second way,110 but the former cyclization with ethyl benzoylacetate gave no pyran.8 If asymmetrically substituted 1,3-cyclohexadienone components are used, the formation of mixtures of isomeric 2//-pyrans may be expected, as shown in Eq. (2)."°... 

Fig. 3.73 Decoupled spectrum of crotonaldehyde. Data reproduced from W. McFarlane and R. F. M. White (1972). Techniques of High Resolution Nuclear Magnetic Resonance Spectroscopy. London Butterworths, p. 28.

This 1,3-dipolar cydoaddition not only gave excellent results but was also found to be very general with regard to the nitrone component. Several types of aryl- and alkyl-substituted nitrone have been applied successfully. Irrespective of the substitution pattern, high diastereomeric ratios and enantioselectivity were obtained (see Scheme 8.9, products 35a,d,f,g). Variation of the N-alkyl group is also possible. As can be see from Scheme 8.9 (see, e.g., products 35a-c), the reactions also proceed well when an N-allyl and N-methyl-substituted nitrone is used. Acrolein, 32b, and crotonaldehyde, 32a, were used as the aldehyde component. It is noteworthy that this reaction is also suitable for use on a larger scale, as has been demonstrated by the 25 mmol-scale preparation of endo-35a (98% yield, 94% ee) starting from nitrone 31a and crotonaldehyde. 

Coupling, of benzenediazonium chloride with acetoacetic add, 32, 84 of diazotized f>-aminoacetophenone with quinone, 34, 1 of diazotized 3,5-dichloro-2-amino-benzoic acid to give 4,4, 6,6 -tetra-chlorodiphenic acid, 31, 96 of diphenyldichloromethane to tetra-phenylethylene, 31, 104 Creosol, 33,17 Crotonaldehyde, 33, 15 34, 29 diethyl acetal, 32, 5 Cyanamide, 34, 67 Cyanoacetamide, 32, 34 Cyanoacetic acid, 31, 25 />-Cyanobenzaldehyde, 30, 100 3-Cyano-5,6-dimethyl-2(l)-pyridone, 32, 34... 

The process is quite general for simple dienes and aldehydes. For example, the reaction of acrolein with cyclopentadiene, cyclohexadiene, or 2,3-dimethyl-l,3-butadiene gives cycloadducts with 8(F-84 % ee and exolendo = 12/88-< 1/99. The a-substituent on the dienophile increases the enantioselectivity (acrolein compared with methacro-lein). When there is /3-substitution in the dienophile, as in crotonaldehyde, the cycloadduct is almost racemic. On the other hand, for a substrate with substituents at both a and ji positions, high ee is observed, as for 2-methylcrotonaldehyde and cyclopentadiene (90 % ee, exolendo = 97/3). The active boron catalyst is beheved to have the structure shown in Eq. (8), with a five-membered ring and a free carboxyl group. The latter seems not to be crucial for the enantioselectivity because eomparable results are obtained when the carboxylic group is transformed into an ester. 

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