Olefins electron deficient

Versatile [3 + 2]-cydoaddition pathways to five-membered carbocydes involve the trimethylenemethane (= 2-methylene-propanediyl) synthon (B.M. Trost, 1986). Palladium(0)-induced 1,3-elimination at suitable reagents generates a reactive n -2-methylene-l,3-propa-nediyl complex which reacts highly diastereoselectively with electron-deficient olefins. The resulting methylenecyclopentanes are easily modified, e. g., by ozonolysis, hydroboration etc., and thus a large variety of interesting cyclopcntane derivatives is accessible. 

Tertiary bismuthines appear to have a number of uses in synthetic organic chemistry (32), eg, they promote the formation of 1,1,2-trisubstituted cyclopropanes by the iateraction of electron-deficient olefins and dialkyl dibromomalonates (100). They have also been employed for the preparation of thin films (qv) of superconducting bismuth strontium calcium copper oxide (101), as cocatalysts for the polymerization of alkynes (102), as inhibitors of the flammabihty of epoxy resins (103), and for a number of other industrial purposes. 

REDUCTIVE ARYLATION OF ELECTRON-DEFICIENT OLEFINS 4- (4-CHLQROPHEHYL1 BirrAN-2-OHE (2-Butanone, 4-(4-ch1oropheny11-1... 

Homolytic cleavage of dlazonlum salts to produce aryl radicals is induced by titan1um(III) salt, which is also effective in reducing the a-carbonylalkyl radical adduct to olefins, telotnerization of methyl vinyl ketone, and dimerization of the adduct radicals. The reaction can be used with other electron-deficient olefins, but telomerization or dimerization are important side reactions. 

REOUCTIVE ARYLATIQN OF ELECTRON-DEFICIENT OLEFINS BY ARENEDIAZONIUM SALTS INDUCED BY TITANIUM(III) SALTS... 

The major difference in reactivity between CF3OF and FCIO3 lies in the capacity of the former to react with olefins without the benefit of an electron releasing group and even with electron deficient olefins such as a,y5-un-saturated ketones. Reactions with nonactivated double bonds indicate the presence of an oc-fluoro cationic intermediate [e.g., (64)] as exemplified by the reaction with the -3-ketone (63), which yields the fluorophenol (65). 

The discovery of palladium trimethylenemethane (TMM) cycloadditions by Trost and Chan over two decades ago constitutes one of the significant advancements in ring-construction methodology [1]. In their seminal work it was shown that in the presence of a palladium(O) catalyst, 2-[(trimethylsilyl)methyl]-2-propen-l-yl acetate (1) generates a TMM-Pd intermediate (2) that serves as the all-carbon 1,3-di-pole. It was further demonstrated that (2) could be efficiently trapped by an electron-deficient olefin to give a methylenecyclopentane via a [3-1-2] cycloaddition (Eq. 1). 

Scheme 2.1 Proposed mechanism for TMM [3+2 cycloaddition with an electron deficient olefin...

Although the base-catalyzed addition of nitroalkanes to electron-deficient olefins has been extensively used in organic synthesis fsee Michael addition Chapter 4, it is only recently that the reaction has been extended to the cyclopropanadon reaction. In 1978, it was reported that the anion of nitromethane reacts with certain highly electron-deficient olefins to produce cycloptopanesingoodyieldrEq. 7.36. More recently, this reaction has been extended to more general cyclopropanadons, as shown in Eqs. 7.37 and 7.38, in which potassittm salts of nitroalkanes are employed in DMSO as alkylidene transfer reagents." ... 

Alttmina-supported KF is an effecdve reagent for Michael addidon of nitroalkanes to electron-deficient olefins. Subsequent cycloalkyladons afford cyclopropanes.However, the reacdo n of a,fi-ttnsantrated ketones v/ithnitroalkanesin the presence of KF-A1,0 in acetonitrile gives 4,5-dihydrofliranes fEq. 7.39. ... 

In some cases, no cycloalky ladon is observed by the reacdon of uittomethane v/ith electron-deficient olefins v/ilh cyano and methoxycarbonyl groups The reacdon affords new, highly fiincdonalLzed cyclohexenes in the presence of catidydc amount of piperidine under solvent- free conchdons v/ith focused microwave irradiadon fEq 7 41 ... 

An important virtue of the Heck reaction is that it can be applied with much success to essentially every type of olefin, although electron-deficient olefins are particularly well-suited. Moreover, the Heck reaction tolerates a variety of functional groups, and often does not require rigorous exclusion of oxygen and water.llb In fact, many alkene arylations proceed very efficiently in water.14... 

The ability of Fischer carbene complexes to transfer their carbene ligand to an electron-deficient olefin was discovered by Fischer and Dotz in 1970 [5]. Further studies have demonstrated the generality of this thermal process, which occurs between (alkyl)-, (aryl)-, and (alkenyl)(alkoxy)carbene complexes and different electron-withdrawing substituted alkenes [6] (Scheme 1). For certain substrates, a common side reaction in these processes is the insertion of the carbene ligand into an olefinic C-H bond [6, 7]. In addition, it has been ob-... 

Asymmetric versions of the cyclopropanation reaction of electron-deficient olefins using chirally modified Fischer carbene complexes, prepared by exchange of CO ligands with chiral bisphosphites [21a] or phosphines [21b], have been tested. However, the asymmetric inductions are rather modest [21a] or not quantified (only the observation that the cyclopropane is optically active is reported) [21b]. Much better facial selectivities are reached in the cyclopropanation of enantiopure alkenyl oxazolines with aryl- or alkyl-substituted alkoxy-carbene complexes of chromium [22] (Scheme 5). 

Methyl-2(17/)-quinoxalinone (109) and 2-methylacrylonitrile (110) gave the photoadduct, l,2a-dimethyl-3-oxo-2,2a,3,4-tetrahydro-l//-azeto[ 1,2-u]quinoxa-line-l-carbonitrile (111) (CH2CI2, MeOH, hv, N2, <15 h >95%) also analogs using significantly electron-deficient olefines. 

Radical-based carbonylation procedures can be advantageously mediated by (TMSlsSiH. Examples of three-component coupling reactions are given in Reactions (74) and (75). The cascade proceeds by the addition of an alkyl or vinyl radical onto carbon monoxide with formation of an acyl radical intermediate, which can further react with electron-deficient olefins to lead to the polyfunctionalized compounds. ... 

Intramolecular nitrone cycloadditions often require higher temperatures as nitrones react more sluggishly with alkenes than do nitrile oxides and the products contain a substituent on nitrogen which may not be desirable. Conspicuously absent among various nitrones employed earlier have been NH nitrones, which are tautomers of the more stable oximes. However, Grigg et al. [58 a] and Padwa and Norman [58b] have demonstrated that under certain conditions oximes can undergo addition to electron deficient olefins as Michael acceptors, followed by cycloadditions to multiple bonds. We found that intramolecular oxime-olefin cycloaddition (lOOC) can occur thermally via an H-nitrone and lead to stereospecific introduction of two or more stereocenters. This is an excellent procedure for the stereoselective introduction of amino alcohol functionality via N-0 bond cleavage. 

The final method was an electrochemical reductive dimcrisation working extremely efficiently and capable of dimerising many electron-deficient olefins. 

A photo-induced dihydroxylation of methacryamide by chromium (VI) reagent in aqueous solution was recently reported and may have potential synthetic applications in the syn-dihydroxylation of electron-deficient olefins.63 Recently, Minato et al. demonstrated that K3Fe(CN)6 in the presence of K2C03 in aqueous rm-butyl alcohol provides a powerful system for the osmium-catalyzed dihydroxylation of olefins.64 This combination overcomes the disadvantages of overoxidation and low reactivity on hindered olefins related to previous processes (Eq. 3.14). 

Subsequently, stoichiometric asymmetric aminohydroxylation was reported.78 Recently, it was found by Sharpless79 that through the combination of chloramine-T/Os04 catalyst with phthalazine ligands used in the asymmetric dihydroxylation reaction, catalytic asymmetric aminohydroxylation of olefins was realized in aqueous acetonitrile or tert-butanol (Scheme 3.3). The use of aqueous rerr-butanol is advantageous when the reaction product is not soluble. In this case, essentially pure products can be isolated by a simple filtration and the toluenesulfonamide byproduct remains in the mother liquor. A variety of olefins can be aminohydroxylated in this way (Table 3.1). The reaction is not only performed in aqueous medium but it is also not sensitive to oxygen. Electron-deficient olefins such as fumarate reacted similarly with high ee values. 

Thus we end up with an oxygen atom which is somewhat electron deficient and a carbon atom which is electron rich. The oxygen then would be expected to behave as an electrophilic reagent and the carbon (or rather the regions bounded by the w orbital) should behave as a nucleophilic reagent. The amphoteric nature of the carbonyl n- n singlet state is mirrored in its reactivity toward electron-rich and electron-deficient olefins. 

Alumina-supported KF is an effective reagent for Michael addition of nitroalkanes to electron-deficient olefins. Subsequent cycloalkylations afford cyclopropanes.37 However, the reaction of a, 3-unsaturated ketones with nitroalkanes in the presence of KF-A1203 in acetonitrile gives 4,5-dihydrofuranes (Eq. 7.39).40... 

In some cases, no cycloalkylation is observed by the reaction of nitromethane with electron-deficient olefins with cyano and methoxycarbonyl groups. The reaction affords new, highly functionalized cyclohexenes in the presence of catalytic amount of piperidine under solvent-free conditions with focused microwave irradiation (Eq. 7.41).42... 

The criss-cross addition of azines of aromatic aldehydes with various electron-deficient olefins in which the double bond is terminal, for example, methyl acrylate, acrylonitrile, or in which allylic substituents do not sterically hinder the reaction, for example, maleic anhydride, is well known and was duly covered in CHEC-II(1996)<1996CHEC-II(8)747>, as well as in a review <1997ALD97>. Recently, the reaction has been used for the preparation of hyperbranched polymers <1998MI2655, 2002MAC712>. 

The homo-coupling of benzylic halides appears to proceed via benzylnickel intermediates similar to that of aryl halides. The intermediate, benzylnickel halide, was successfully trapped with electron deficient olefins. 

Trapping experiments with electron deficient olefins such as acrylonitrile and 3-buten-2-one gave the expected 1,4-adducts from the proposed acylnickel intermediates. This provides strong support for the proposed mechanism. It was also demonstrated that allylic, vinylic and pentafluorophenyl halides could be cross-coupled with acid chlorides to give the corresponding ketones in good yields. 

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