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Michael functions acceptor

The conjugate system of the C-2 nitroalkenes should posses some interesting chemical reactivity and it should be an excellent Michael reaction acceptor with reactive nucleophiles. Moreover, the steric effect of the bulky 1,6-anhydro ring should be similar to that of levoglucosenone. As a consequence, nitroalkenes are excellent precursors for the stereoselective introduction of an additional sugar moiety at C-2 with subsequent additional functional group such as nitromethylene or its reduced/acetylated analog. Moreover, this unsaturated C-2 functionality additionally fixes the conformation of the system and most importantly sterically hinders the P-D-face of both enone molecules. [Pg.6]

The stereoselective, one-step synthesis of (l,4)-5-thiodisaccharides (7-2) is a classical example (Scheme 2) of exploiting the excellent functionality of levoglucosenone as Michael reaction acceptor. The methodology of functionalization of C-2 either via conventional and stereoselective reduction, or oximation and then stereoselective reduction of the oximino functionality is unique in providing both classes of 5-thio-disaccharides. Moreover, the C-2 amino functionalized nonhydrolyzable 5-thio-disaccharide, after deprotection of C-2 acetamido function represents a convenient molecular scaffold for the generation of diverse libraries of peptidomimetics as a selected class of glycoconjugates. [Pg.81]

Another category of reactive enones is 4-deoxy-l,2-0-isopropylidene-L-glycero-pent-4-enopyrano-3-ulose, originally synthesized by Klemer and Jung (25) and currently explored by us as an extremely useful new chiral building block for stereoselective functionalization reactions, especially as Michael addition acceptors (Scheme 6). [Pg.85]

A process patent and subsequent publication by Fujita and cowoikers, disclosed an improved, large-scale synthesis of fingohmod. In particular, the problem of competing styrene formation that plagued the original synthesis was addressed. In this approach, a Friedel-Crafts acylation of phenylethyl bromide (8) with octanoyl chloride yielded ketone 9 (Scheme 2). Treatment of ketone 9 with sodium ethoxide affords the expected styrene product (10) however, in this case, styrene 10 can function as a Michael-type acceptor to generate the desired amino malonate product 11 in 55% yield (2 steps). Next, hydrogenolysis of the ketone with palladium on carbon in ethanol provided... [Pg.264]

An excellent synthetic method for asymmetric C—C-bond formation which gives consistently high enantioselectivity has been developed using azaenolates based on chiral hydrazones. (S)-or (/ )-2-(methoxymethyl)-1 -pyrrolidinamine (SAMP or RAMP) are chiral hydrazines, easily prepared from proline, which on reaction with various aldehydes and ketones yield optically active hydrazones. After the asymmetric 1,4-addition to a Michael acceptor, the chiral auxiliary is removed by ozonolysis to restore the ketone or aldehyde functionality. The enolates are normally prepared by deprotonation with lithium diisopropylamide. [Pg.975]

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. [Pg.30]

Version (b) has a four-channel flow guidance that encompasses two mixing tees in two simple mixing tees (Figure 4.5) [8]. An example of this function is the flow guidance for the Michael addition. In a first step, the base and 1,3-dicarbonyl compound streams merge. The enolate stream thus formed is then mixed with the Michael acceptor. Microporous silica frits are set into the channels to minimize... [Pg.383]

Nitroolefins are good Michael acceptors and their reactivity toward diethylzinc is different depending on the presence or absence of Lewis acids. Since the nitro group can be further transformed to a variety of useful containing functionalities,76,7641 the asymmetric 1,4-additions of nitroolefins may provide an easily accessible pathway to highly versatile optically active synthons. [Pg.382]

We have also developed targeted library approaches towards cysteine proteases, which are important pharmaceutical targets due to their role in the pathogenesis of many diseases.1251 A common feature of virtually all cysteine protease inhibitors is an electrophilic functionality, such as a carbonyl or a Michael acceptor, which can react with the nucleophilic active site cysteine residue. We specifi-... [Pg.72]

With a.-bromo Michael acceptors. Condensation reaction of 2-aminothiazoline with a-bromo-a,/3-unsaturated compounds, commercially available or generated in situ, provided a route to functionalized 2,3,5,6-tetrahydro-imidazo[2,l-3]thiazoles 411 (Equation 187) <1994H(38)2593>. [Pg.179]

Most reactive metabolites produced by CYP metabolic activation are electrophilic in nature, which means that they can react easily with the nucleophiles present in the protein side chains. Several functional groups are recurrent structural features in M Bis. These groups have been reviewed by Fontana et al. [26] and can be summarized as follows terminal (co or co — 1) acetylenes, olefins, furans and thiophenes, epoxides, dichloro- and trichloroethylenes, secondary amines, benzodioxoles (methylenediox-yphenyl, MDP), conjugated structures, hydrazines, isothiocyanates, thioamides, dithiocarbamates and, in general, Michael acceptors (Scheme 11.1). [Pg.270]

Donor- and acceptor-substituted allenes with general structures 1 or 2 (Scheme 8.1) have the most obvious synthetic potential among functionalized allene derivatives and therefore they serve as versatile building blocks in many synthetic endeavors [1], As expected, the reactivity of the double bonds of 1 or 2, which are directly connected to the activating substituents, are strongly influenced by these groups. Hence there is enol ether or enamine reactivity of 1 and Michael acceptor type chemistry of 2. In addition, the terminal double bonds are also influenced by these functional groups. [Pg.425]

Allenic amino acid derivatives 50, which are of special interest as selective vitamin Bg decarboxylase inhibitors [35], are accessible through 1,6-cuprate addition to 2-amino-substituted enynes 49 (Eq. 4.22) [36]. Because of the low reactivity of these Michael acceptors, however, the reaction succeeds only with the most reactive cuprate the t-butyl cyano-Gilman reagent tBu2CuLi-LiCN. Nevertheless, the addition products are obtained with good chemical yields, and selective deprotection of either the ester or the amino functionality under acidic conditions provides the desired target molecules. [Pg.157]

Diastereofacial selection on addition of organocoppper reagents to chiral y-alkyl-substituted Michael acceptors has been investigated less extensively, due to the usually low selectivities generally observed for these systems [38, 39]. This is exemplified by the reaction of E and Z enoates 90 (Scheme 6.19). Thus, either syn-91 or anti-93 is formed upon conjugate addition with BF3-modified reagents, as a function of enoate geometry. The stereochemistry of the reaction is in accordance with the modified Felkin-Anh model [40]. [Pg.198]

Aliphatic compounds containing terminal gem-dinitro functionality form adducts with Michael acceptors.Of particular interest is the reaction of a,a,o),a)-tetranitroalkanes with Michael acceptors. ° Most a, o, y, y-tetranitroalkanes will react with two equivalents of Michael acceptor to form bis-adducts, like in the case of 1,1,4,4-tetranitrobutane, which reacts with two equivalents of methyl vinyl ketone, methyl acrylate, acrylonitrile etc. ° The influence of steric effects becomes apparent with a,a,y,Y-tetranitroalkanes, like 1,1,3,3-tetranitropropane, which can form either mono-adducts or bis-adducts depending on the Michael acceptor used 1,1,3,3-tetranitropropane will only react with one equivalent of methyl acrylate and the sole product of this reaction is methyl 4,4,6,6-tetranitrohexanoate. °... [Pg.36]

Mobashery and co-workers also reported the synthesis and inhibitory apph-cation of 2 -N02 derivatives of neamine and kanamycin (Scheme 4.28). Using the metal-chelating method, the 2 -NH2 was selectively unmasked and then oxidized into 2 -N02, which will increase the acidity of 2 -H. Upon phosphorylation at the 3 -0H, elimination of phosphate will lead to the formation of a nitroalkene intermediate, 198, that can function as a Michael acceptor and... [Pg.171]

In the presence of thiourea catalyst 122, the authors converted various (hetero) aromatic and aliphatic trons-P-nitroalkenes with dimethyl malonate to the desired (S)-configured Michael adducts 1-8. The reaction occurred at low 122-loading (2-5 mol%) in toluene at -20 to 20 °C and furnished very good yields (88-95%) and ee values (75-99%) for the respective products (Scheme 6.120). The dependency of the catalytic efficiency and selectivity on both the presence of the (thio) urea functionality and the relative stereochemistry at the key stereogenic centers C8/C9 suggested bifunctional catalysis, that is, a quinuclidine-moiety-assisted generation of the deprotonated malonate nucleophile and its asymmetric addition to the (thio)urea-bound nitroalkene Michael acceptor [279]. [Pg.264]

The same hexacyclic enedione has been converted to a series of Cj -heptaquinane derivatives via the alcohol 819 which is produced by condensation with ethyl formate in base The hydroxyl group in 819 can be readily functionalized, although loss of water to arrive at 820 occurs remarkably readily, despite the inherent strain of this system (Scheme XCIX). The conjugated double bond in 820 is understandably a good Michael acceptor, a property which was utilized to prepare 821. [Pg.88]


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See also in sourсe #XX -- [ Pg.388 , Pg.663 ]




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Michael acceptor

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