Enones, 367. reacting with

Isoxazolines 79, obtained from aromatic nitrile oxide cycloadditions to cyclohex-2-enone, reacted with nickel peroxide to give 3-aryl-6,7-dihydro[l] benzoisoxazol-4(5// )-ones 80. In contrast, the corresponding 2-bromocyclohex-2-enone underwent nitrile oxide cycloaddition, followed by dehydrobromination, to afford the regioisomeric 3-aryl-4,5-dihydro[l]benzoisoxazol-7(6//)-ones 81 (Scheme 1.23) (242). 

Acetophenone also yields pyrylium salts on treatment with acids, such as hydrogen chloride and sulfuric acid, or with boron trifluoride. The initially formed enone undergoes partial deacylation by the acid, whilst unchanged enone reacts with the acyl cation so produced to give the pyrylium salt. 

Stereoselective acyclic enolization2 This reaction can sometimes be achieved by conjugate reduction of acyclic a,(3-enones by lithium tri-sec-butylborohydride (1). When an enone reacts with 1 mainly by 1,2-reduction Li/NH3 can be used for conjugate reduction. In at least one case reduction with 1 is more stereoselective than that with Li/NH3. The stereoselectivity in general can be correlated with conformational preferences of enones.3... 

In the case of alanes (Table XII), we have shown that reagents that favor 1,2-addition to a-enones react with retention at silicon, whereas those that favor 1,4-addition react with inversion (57). 

Conjugate reductions of a,(l-enones.2 a., fi-Enones react with triisobutylaluminum in pentane solution to give products of 1, 2-addition and 1, 2-reduction. The former... 

Cyclic enones reacted with 4-fe/t-butyl thiophenol (% ee achieved) ... 

Imagine a cyclic p-fluoro-enone reacting with a secondary amine in a conjugate substitution reaction. The normal addition to form the enolate followed by return of the negative charge to expel the fluoride ion gives the product. 

The -nitroketone 151, prepared by Michael addition of ethyl nitroacetate to the appropriate enone, reacts with formamidinesulfinic acid and triethylamine to afford pyrrole-2-carboxylate 153, presumably via the oxime or imine 152 (Scheme 80) <1995TL9469>. 

Addition to -alkylthio-a., -enones. The stereochemistry of conjugate addition-elimination of organocupratcs with (E)-p-alkylthireaction with R CuLi in ether. 

A nice example of the solvent-dependent dual reactivity of an electrophilic crypto-cationic species has been given by Hiinig et al. [663]. Ambident electrophilic a-enones react with nucleophiles such as the anion of the benzaldehyde O-(trimethylsilyl)-cyanohydrin (Nu ) in diethyl ether exclusively by 1,4-addition. In tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME), the 1,2-adduct is formed predominantly on the addition of HMPT or [12]crown-4 it is formed exclusively cf. Eq. (5-133). 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophihc selenium species. " They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nifro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding a ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

Enones react with benzofuroxan in the presence of a primary or secondary amine to afford specific quinoxaline monoxides the course of the reaction depends on the nature of the base. The usefulness of these reactions for synthesis are limited by low yields and the lack of universality for enones as substrates. 

These enones reacted with substituted phenacyl pyridinium bromides and ammonium acetate under pyridine ring formation. Cleavage was performed with 25 % TFA/CH2CI2. Twelve compounds were synthesized, with yields of the crude products ranging from 50 % to 85% (HPLC-purities 76-97%). 

Nitrosopropio enone reacts with hydrogen bromide in benzene at ambient temperature to form a 5-bromo-2,l-benzisoxazole as the main product while the corresponding 5- and 7-chloro derivatives may be formed when hydrogen chloride is used. A similar substrate may be deoxygenatively cyclized with triphenylphosphine in good-to-excellent yields. 

The most studied case is that of a cyclic enone reacting with an olefin. In these systems several trends are observed. The reaction proceeds from T, which may be either n,iT or -IT,IT, and triplet biradicals are likely involved. Electron-rich olefins react more rapidly and add with predictable regiochemistry. Cis-trans stereochemistry in the olefin is lost in the cycloaddition, and trans fused rings can form. 

The first enantioselective organocatalytic oxo-Michael reaction to enones was reported by Falck [109]. Falck developed the intramolecular addition of boronic acids hemiesters to enones catalyzed by thiourea catalysts. Alkyl, aryl, and heteroaryl y-hydroxy enones react with phenylboronic acid to furnish the corresponding boronic hemiesters 118, which after oxidative cleavage of the resulting dioxaboro-lane renders the chiral 1,2 diols 119 in excellent yields and enantioselectivities (Scheme 33.34). 

Ye, Liang, and coworkers reported the addition of diphenylphosphine oxide to enones catalyzed by a bifunctional primary amine thiourea catalyst (127) derived from cinchona alkaloid (Scheme 33.38) [119], Cyclic and acyclic enones react with phosphine oxides under the optimized conditions to furnish the phosphine derivatives 128 in excellent yields and enantioselectivities. The primary amine of the catalyst activates the enone via an iminium, while the thiourea moiety activates and directs the phosphine group. 

The area of asymmetric Michael reaction of 1,3-dicarbonyl to enone can be simply divided into three types (Scheme 9.2). In type I, the Michael acceptor (enone) reacts with the prochiral Michael donor to induce a chiral center on the Michael donor side. In type II, the prochiral Michael acceptor reacts with the Michael donor to give an asymmetric center on the Michael acceptor side. For type III, the prochiral Michael acceptor reacts with the prochiral Michael donor to afford adjacent chiral centers on both sides in one step. Because (3-substituted enone is often used as a Michael acceptor in both type II and type III, the catalytic asymmetric Michael addition is generally divided into two classes 1) Michael addition of vinyl ketone and 2) Michael addition of (3-substituted enone. In the asymmetric Michael addition of class I, vinyl ketone is often employed as a Michael acceptor to react with (3-keto ester for... 

A further improvement in the cuprate-based methodology for producing PGs utilizes a one-pot procedure (203). The CO-chain precursor (67) was first functionalized with zirconocene chloride hydride ia THF. The vinyl zirconium iatermediate was transmetalated direcdy by treatment with two equivalents of / -butyUithium or methyUithium at —30 to —70° C. Sequential addition of copper cyanide and methyUithium eUcited the /V situ generation of the higher order cyanocuprate which was then reacted with the protected enone to give the PG. 

Interestingly the Skraup/Doebner-von Miller reaction has been used to prepare a number of spiro-compounds. Aniline was reacted with enone 42 in the presence of iodine to yield dihydroquinoline 43 in acceptable yields. 

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