Crotonaldehyde complexes with group

Crotonaldehyde complexes with group VIB metals, 12 221-223 18-Crown-6, conformers, 42 126, 128 Crown conformation, in polysulfidemetal complexes, 31 115... 

Complex hydrides can be used for the selective reduction of the carbonyl group although some of them, especially lithium aluminum hydride, may reduce the a, -conjugated double bond as well. Crotonaldehyde was converted to crotyl alcohol by reduction with lithium aluminum hydride [55], magnesium aluminum hydride [577], lithium borohydride [750], sodium boro-hydride [751], sodium trimethoxyborohydride [99], diphenylstarmane [114] and 9-borabicyclo[3,3,l]nonane [764]. A dependable way to convert a, -un-saturated aldehydes to unsaturated alcohols is the Meerwein-Ponndorf reduction [765]. 

The 2-methylenecyclopentanone initially formed presumably rearranges into 2-methyl-2-cyclopentenone under the reaction conditions. The final step of the mechanism, elimination of the cobalt carbonyl group, is not well understood but the same kind of elimination and reduction reactions occur with known 3-ketocobalt complexes. As mentioned above, crotonaldehyde, acrolein (27), and glyddaldehyde (38) react rapidly with cobalt hydrocarbonvl under similar conditions to give reduction products, rather than forming stable alkyl- or acyl-cobalt tetracarbonyl derivatives. 

Helmchen and co-workers [13] independently achieved similar results with catalysts of CAB 3 derived from valine (R = /-Pr). When R is 2,4,6-trimethylphenyl, the cycloaddition of crotonaldehyde and cyclopentadiene occurs with 72 % ee exo endo = 3 97) in the presence of 0.2 equiv. chiral catalyst. More recently, the same authors systematically investigated the influence of different experimental conditions on the enantioselectivity [15]. Improved enantioselectivity was obtained in THE or by addition of THE (ee up to 86 %). A transition-state model is proposed for prediction of the absolute configuration of the adducts (Eig. 2). In this model, the R group directs the R S02 group to the opposite side of the ring, where the latter group again participates in trans attack on boron. The conformation of the complexed enal has been determined to be s-cis, as has the coordination of carbonyl to boron syn to H. This model correctly predicts the outcome of all the examples studied. 

Radical anions generated from metal-organic compounds are another group of initiators. Based on polarographic investigations and Huckel calculations it was shown that the polymerization of crotonaldehyde with benzophenone radical anions proceeds via formation of a complex radical anion of crotonaldehyde [174]. This complex accepts a... 

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