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Carbenoids deoxygenation

Functionalized zinc carbenoids have been prepared from carbonyl compounds by an indirect strategy. The deoxygenation of a carbonyl compound to an organozinc carbenoid can be induced by a reaction with zinc and TMSCl. Therefore, the aldehyde or ketone, when treated with TMSCl or l,2-bis(chlorodimethylsilyl)ethane in the presence of an alkene, generates the cyclopropanation product. This method is quite effective for the production of alkoxy-substituted cyclopropane derivatives. A 55% yield of the... [Pg.241]

Nitrile oxides display three types of reactivity (apart from isomerization and deoxygenation) 1,3-cycloaddition, 1,3-addition, and dimerization to furoxans. The first can give isoxazolines and isoxazoles directly. The second can give isoxazolines and isoxazoles indirectly. The third (which may be regarded as a carbenoid reaction,62 but see also Lo Vecchio et al.63) is an undesirable side reaction as far as the synthesis of isoxazoles is concerned. Thus, although many methods for generating nitrile oxides are available, and in some cases they may be isolated and used, methods capable of generating them in the presence of the substrate are preferred. [Pg.158]

A deoxygenative conversion of carbonyl compounds into cyclopropanes (Scheme 2) stretches the bounds of the conventional cyclopropanation reactions that employ the C=C double bond and a carbenoid intermediate. [Pg.109]

In fact, only in some cases are real carbenoid species involved in these reactions. The reactions employing oxophilic metals such as Zn, Fe, Sm, and In were reported [9], and representative examples are given in Scheme 3. Such reactions exhibit obvious synthetic limitations, since only aromatic (unsaturated) carbonyl compounds can be used, and/or cyclopropanes of a very specific structure obtained. The Kulinkovich and related reactions, involving dianion equivalents (1, Scheme 1), represent the only synthetically useful deoxygenative process at present. [Pg.109]

Carbenes or carbenoids have also been reported to deoxygenate epoxides. To generate these species, dimethyl diazomalonate/rhodium(II) acetate and 9-diazofluorene 44 have been employed both reagents show high stereoselectivity. For example, ciJ-2-butene oxide is converted to cir-alkene with more than 93% retention under irradiation (350 nm) using 9-diazofluorene, and functional groups, such as carbonyl, can survive using diazomalonate and rhodium(II) acetate (equation 49). [Pg.890]

Conjugated trienes are amongst the products accessible via the Zn/TMSCl mediated dimerisation of carbonyl substrates, including a, 0-unsaturated ketones. The reaction is thought to proceed via the formation of an organozinc carbenoid which combines with a second equivalent of carbonyl substrate to produce an intermediate epoxide, which then undergoes deoxygenation, (Scheme 67). [Pg.34]

After copper and palladium, rhodium is the third most important transition metal for the synthesis of the indole ring. For a 2007 review on this reaction, see Patil and Paiil [1], Some early examples (Scheme 1) are Alper s rhodium reaction of 2-aryl-2/7-azirines to give 2-styiylindoles (equation 1) [2], Watanabe s Rh-catalyzed Fischer indole synthesis (equation 2) [3], Ucciani s 3-methylindole synthesis via the hydroformylation of o-nitrostyrene (equation 3) [4], and Burst s preparation of 3-acetyl-2-hydrox-yindoles from the Rh-catalyzed decomposition and carbenoid aromatic C-H bond insertion (equation 4) [5]. Narasaka extended Alper s 2-aryl-2//-azirine reaction to a Rh(II)-catalyzed synthesis of 2,3-disubstituted indoles [6], and both Cenini [7] and Alper [8] stretched the deoxygenation of o-nitrostyrenes to give indoles. Burst s Rh-catalyzed decomposition of a-diazo carbonyl compounds was used by Bauban [9] and Jha [10] in the synthesis of substituted oxindoles. [Pg.632]

From the following reaction with cyclohexene, it was concluded that the deoxygenation of aldehydes and ketones by Zn/Cu and TMSCI in diethyl ether takes place via a carbenoid intermediate [86a]. [Pg.111]

C-H Insertion. Insertion of carbenoid species generated from dimethyl diazomalonate in the presence of Rh into activated C-H bonds proceeds in moderate yields (eq 33). Sometimes undesired insertion into the C-H bond adjacent to the heteroatom complicates the utilization of Ganem epoxide deoxygenation procedure (eq 34). ... [Pg.300]


See other pages where Carbenoids deoxygenation is mentioned: [Pg.209]    [Pg.247]    [Pg.107]    [Pg.129]    [Pg.207]    [Pg.49]    [Pg.272]    [Pg.274]    [Pg.274]   


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