A,P-Unsaturated acid derivatives

In addition to the availability issues of the oxazolidinone unit, there has been some reluctance to scale up the reactions because formation of the A-acyl derivatives usually employs n-butyl lithiiun as a base. We have found a simple acylation procedure that avoids the use of this strong base and copper salts [11,12], Our procedure uses an acid chloride or anlrydride (symmetrical or mixed) with triethylamine as the base in the presence of a catalytic amount of DMAP. The reaction is general and provides good yields even with a.p-unsaturated acid derivatives (Scheme 7) [13],... [Pg.306]

Dipolar cycloadditions of five-member cyclic nitrones to a,p-unsaturated acid derivatives 99H(50)1213. [Pg.246]

The outstanding chemical property of cyanohydrins is the ready conversion to a-hydroxy acids and derivatives, especially a-amino and a,P-unsaturated acids. Because cyanohydrins are primarily used as chemical intermediates, data on production and prices are not usually pubUshed. The industrial significance of cyanohydrins is waning as more direct and efficient routes to the desired products are developed. Acetone cyanohydrin is the world s most prominent industrial cyanohydrin because it offers the main route to methyl methacrylate manufacture. [Pg.410]

Detailed NMR assignments for a range of bispyranones and some dihydro derivatives have followed their unambiguous syntheses through the Lewis acid-mediated reaction between 4-hydroxypyranones and a,P-unsaturated acids, a reaction which has potential in natural product synthesis (Scheme 39) <00TL1901>. [Pg.327]

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... [Pg.756]

A P,Y-unsaturated carbonyl compoimd exposed to acid or base is usually converted rapidly into an a,P-unsaturated carbonyl derivative. This isomerization is easily interpreted by considering enolization. [Pg.354]

Alkene acylation may be used in the synthesis of cyclic products by appropriately selecting the alkene and the acid derivative. When a,P-unsaturated acid halides react with cycloalkenes, the intermediate undergoes cyclization to yield octalones and indanones 112... [Pg.419]

Enoyl-CoA hydratase. A specific example of the reaction in Eq. 13-6 is the addition of water to fra s-a,P-unsaturated CoA derivatives (Eq. 13-7). It is catalyzed by enoyl-CoA hydratase (crotonase) from mitochondria and is a step in the P oxidation of fatty acids (Fig. 10-4). [Pg.681]

Asymmetric Diels-AUer reactions The observation that simple acyloxy-boranes such as H2BOCOCH=CH2, prepared by reaction of BH3 with acrylic acid, can serve as Lewis acid catalysts for reactions of the a,P-unsaturated acids with cyclopentadiene (15, 2) has been extended to the preparation of chiral acyloxy-boranes derived from tartaric acid. The complex formulated as 3, prepared by reaction of BH3 with the monoacylated tartaric acid 2, catalyzes asymmetric Diels-Alder reactions of a,P-enals with cyclopentadiene with high enantioselectivity. The process is applicable to various dienes and aldehydes with enantioselectivities generally of 80-97 % ee. [Pg.314]

Unfortunately, several important classes of a-diazo ketones cannot be prepared in good yield via these standard methods. a -Diazo derivatives of a.p-unsaturated ketones, for example, have previously proved to be particularly difficult to prepare.1113 12 The acylation of diazomethane with a.p-unsaturated acid chlorides and anhydrides is generally not a successful reaction because of the facility of dipolar cycloaddition to conjugated double bonds, which leads in this case to the formation of mixtures of isomeric pyrazolines. Also problematic are diazo transfer reactions involving base-sensitive substrates such as certain a,p-enones and heteroaryl ketones. Finally, the relatively harsh conditions and lack of regioselectivity associated with the thermodynamically controlled Claisen formylation step in the "deformylative" diazo transfer procedure limit the utility of this method when applied to the synthesis of diazo derivatives of many enones and unsymmetrical saturated ketones. [Pg.138]

Mechanistically, the sequence commences by coupling of the (hetero)aroyl chloride 7 and the aUcyne 4 to give the alkynone 8 (Scheme 43). Upon addition of the tryptamine derivative 73 the enaminone 75 is obtained. Finally, the addition of the a, p-unsaturated acid chloride 71 triggers the aza-annulation reaction to furnish the acyliminium ion 76 which terminates the sequence by a Pictet-Spengler cyclization. [Pg.60]

Catecholborane is a versatile reducing reagent, a mild and convenient alternative to the classical (Clemmensen, using acids and Wolff-Kishner, using bases) reduction procedure of tosylhydrazones. Regiospecific isomerization occurs during the reduction of a,p-unsaturated carbonyl derivatives often leading to unique alkenes (Eqs. 134 and 135) and allenes(Eq. 136) . ... [Pg.81]

Diastereoselective Conjugate Addition of Organometallic Reagents to Chiral a,P-Unsaturated Amides and Imidazolidi-nones Derived from Ephedrine. Grignard reagents (2 equiv) add to chiral a,P-unsaturated amides derived from ephedrine in a 1,4-addition manner with high diastereoselectivities. Subsequent acidic hydrolysis affords optically active p-substituted carboxylic acids with 85-99% ee (eq 3). ... [Pg.323]

The ate complex LiAlHBu"Bu 2 is prepared from DIBAL-H and n-butyllithium in either THF or toluene-hexane. This reagent is more effective for selective 1,2-reduction of enones to the corresponding allylic alcohol than is DIBAL-H alone. The reagent also reduces esters, lactones and acid chlorides to the corresponding alcohols, and epoxides to the respective alcohols. a,p-Unsaturated ketones derived from dehydration of aldol products from I-(arylthio)cyclopropanecarbaldehydes and ketones were selectively reduced by this ate complex or by DIBAL-H itself, yielding the allylic alcohols with minor... [Pg.544]

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... [Pg.1138]

A pictorial overview of the substrate scope is presented in Figure 2.3. More detailed results for synthetically useful reactions are presented in the next sections. Besides a-keto acid derivatives, a-keto acetals, a-keto ethers, and some trifluoromethyl ketones have been shown to give high ee values with Pt-based catalysts. Pd-based catalysts give moderate enantioselectivities for most a,P-unsaturated acids and up to 94% ee for selected pyrones. Nevertheless, for the synthetic chemist, the substrate scope is still relatively narrow, and it is not expected that new important substrate classes will be found soon. On the other hand, the chemoselectivity of this system has not yet been exploited to its full value, and this might hold a potential for synthetically useful applications in the future. [Pg.17]

The [4+2] cycloaddition of chiral a,P-unsaturated ketones, derived from optically pure 2-hydroxy-3,3-dimethylbutyric acid, proceed with high selectivities and in excellent yield at low temperature in the presence of a Lewis acid, e.g. ZnCl2 or BF3-OEt2. Cycloaddition reactions of chiral at iron aciyloyl complexes with cyclopentadiene in the presence of ZnCl2 have been studied by Davies et al... [Pg.52]

Znl2 was applied successfiilly as Lewis-acid in order to increase the diastereoselectivity of the reaction of a cyclic nitrone with a,P-unsaturated imide derivatives. - It is noteworthy that chiral auxiliaries efficient in numerous other transformations, exhibit only low stereoselection in cycloadditions of nitrones. " ... [Pg.121]

Treatment of 1 with two equivalents of nBuLi in a mixture of hexane -THF at -65 °C followed by the addition of the carbonyl compounds gave after hydrolysis the corresponding ot-chloro-a,P-unsaturated acids [242c]. Diethyl 1-chloroalkylphosphonates are used for the preparation of diethyl 1,2-epoxyalkylphosphonates [243-246], and 1-(methylthio)methylphosphonate [247], as well as derivatives of alkyidenediphosphonates and vinylphosphonates [248],... [Pg.73]

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