Unsaturated acids, selective alcohols

BINAP (40a) was first reported as a ligand in an enantioselective hydrogenation in 1980 [172], and provides good selectivity for the reductions of dehydroamino acid derivatives [173], enamides, allylic alcohols and amines, and a,p-unsaturated acids [4, 9, 11, 12, 174, 175]. The fame of the ligand system really came with the reduction of carbonyl groups with ruthenium as the metal [11, 176]. The Rh-BINAP systems is best known for the enantioselective isomerizations... 

Many of the chiral selenium electrophiles have also been employed in cyclization reactions. Various internal nucleophiles can be used and access to different heterocycles is possible. Not only oxygen nucleophiles can be used for the synthesis of heterocyclic compounds, but also nitrogen nucleophiles are widely employed and even carbon nucleophiles can be used for the synthesis of carbacycles with new stereogenic centers. Oxygen nucleophiles have been widely used and some selected examples of selenolactonizations of unsaturated acids 50 and 52 and seleno-etherifications of unsaturated alcohols 54 and 56 are shown in Scheme 10. 

Unsaturated polyesters (UPs) crosslinked with styrene are often used as a matrix of fiber reinforced plastics. Several reports treated the degradation of the crosslinked UPs with high temperature treatment in water (1,2), acetic acid (5), alcohols including glycols (4,5), and amines (6), often in the presence of catalysts. In these literatures, recovery of polymeric materials from the crosslinked UPs was not a main objective. However, in case we can hydrolyze polyester chains selectively, linear polystyrene derivatives can be obtained as recycled materials. 

Two ruthenium complexes, binap 3.43-Ru(OCOR)2(R = Me,CF3) [892] and binap 3.43-RuX2 (X = Cl, Br, I) [893, 894], are quite useful. The acetate and trifluoroacetate complexes of 3.43 induce selective asymmetric hydrogenations of classes of prochiral olefins that are poorly selective with rhodium complexes. These classes include a,(3- or fcy-unsaturated acids and esters, ally alcohols, j3-acylaminoacrylates and enamide precursors of isoquinoline alkaloids [752, 853, 859, 881, 883, 895]. 

Nevertheless, it must be pointed out that the formation of such transient species has never been spectroscopically observed. Native CDs are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols, epoxydation,or oxidation " of olefins, reduction of a,/ -unsaturated acids,a-keto ester,conjugated dienes,or aryl alkyl ketones.Interestingly, chemically modified CDs like the partially 0-methylated CDs show a better catalytic activity than native CDs in numerous reactions such as the Wacker oxidation,hydrogenation of aldehydes,Suzuki cross-coupling reaction, hydroformylation, " or hydrocarboxylation of olefins. Methylated /3-CDs were also used successfully to perform substrate-selective reactions in a two-phase system. 

The spontaneous evolution of a mixture of species corresponds with the selection of those best adapted to wine—which is a hostile acidic and alcoholic environment. The composition of the plasmic membrane, and the various mechanisms, that permit it to react to the aggressiveness of the medium, seem to influence this adaptation. Certain species or strains may also differ in their ability to carry out these transformations. Strains of Lfructivorans adapt better to ethanol than L. plantarum and L. hilgardii, due to a more effective modification of their fatty acids (unsaturation and chain length) (Kalmar, 1995). Unsurprisingly, strains of this species are often identified in fortified wines tainted by lactic disease with an alcohol content between 15 and 20% volume. 

Selective oxidation of secondary alcohols to ketones is usually performed with CrOj/HjSO, I I in acetone (Jones reagent) or with CrOjPyj (Collin s reagent) in the presence of acid-sensitive groups (H.G. Bosche, 1975 C. Djerassi, 1956 W.S. Allen, 1954). As mentioned above, a,)S-unsaturated secondary alcohols are selectively oxidized by MnOj (D.G. Lee, 1969 D. Arndt, 1975) or by DDQ (D. Walker, 1967 H.H. Stechl, 1975). 

A particularly useful reaction has been the selective 1,2-reduction of a, P-unsaturated carbonyl compounds to aHyUc alcohols, accompHshed by NaBH ia the presence of lanthanide haUdes, especially cerium chloride. Initially appHed to ketones (33), it has been broadened to aldehydes (34) and acid chlorides (35). NaBH by itself gives mixtures of the saturated and unsaturated alcohols. 

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