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Dearomatization reactions alkylative

Fernandez, I. Forcen-Acebal, A. Garcia-Granda, S. Lopez-Ortiz, F. Synthesis of functionalized 1,4-cyclohexadienes through intramolecular anionic dearomatization of N-alkyl-N-benzyldiphenylphosphinamides. Insight into the reaction mechanism. /. Org. Chem. 2003, 68, 4472-4485. [Pg.212]

We decided to investigate one final substrate that contained our desired side chain for the intramolecular Diels-Alder cycloaddition as well as a small and removable cyano group. Our synthesis is outlined in Scheme 11. Phenol 53 was alkylated with chloroacetonitrile, then condensed to form 2-cyano benzo-furan 54. Subsequent quatemarization to 56 was accomplished with sodium hydride and a bromocrotcMiate (55) electrophile. Following phenol ether deprotection and reduction of the benzylic ketone with sodium borohydride, we were in a position to evaluate the dearomatization step. Unfortunately, all attempts to access the quinone epoxide 58 under classic or modified Adler-Becker reaction conditions failed. With these results, we closed the book on the second chapter in our vinigrol saga and went back to the drawing board. [Pg.345]

Phenols can be viewed as stable forms of enol tautomers, and phenolate anions display ambident nucleophilicity at oxygen as weU as C2/C6 and C4 (ortholpara positions). Consequently, phenolate anions are susceptible to C—C bond formation upon reaction with appropriate organic electrophiles (e.g., alkyl halides and sulfonates). When bond formation occurs at a substituted arene carbon, a quatonaty centCT is generated, which may lead to isolation of stable cyclohexadienone products and complete a net alkylative dearomatization (Scheme 15.1) [2]. [Pg.400]

Early examples of this reaction involved cyclizations of 4-substituted phenols tethered to alkyl sulfonates and halides [3]. CycMzalions involving carbonyl electrophiles (aldehydes, ketones) and imines have been reported as well, but esters are not sufiSciently electrophilic to react [2]. Subsequent studies established that the facility of these so-called Ai-n cyclizations was strongly affected by the size of the newly formed ring in the order 3>5>6 >4. Since the vast majority of alkylative dearomatizations involve intramolecular cyclizations (thereby avoiding competitive 0-aDcylation reactions), stereoelectronic effects operative in the transition states (resembling the TS of an Sjj2 reaction) are crucially important. These sometimes subtle effects can result in differential reactivity of structurally similar substrates [4]. [Pg.400]

Intramolecular alkylative dearomatization offers a convenient means of constructing spirocyclo-hexadienone ring systems (Scheme 15.1). This reaction has been utilized in a number of total syntheses targeting construction of terpenoid ring systems found in natural products such as cedrene, hinesol, kaurene, p-vetivone, and isolongifolene [5], Subsequently, alkylative dearomatizations have been employed as key steps in approaches toward more complex natural products such as inter alia duocarmycin SA [6], cortistatin A [7], and platensimycin (Scheme 15.2) [8], This last example is notable as it illustrates the ability to employ silyl-protected phenols as masked phenolate anions in high-yielding alkylations. [Pg.400]

Dearomatization of r -benzylpalladium complexes represents an electronically reversed variation on the reactions described earlier. Initial examples utilized allyl and allenyl stan-nanes as nucleophilic components in combination with benzyl halides and invoked mechanisms involving aryl-alkyl Pd(II) intermediates [84]. Subsequently, direct addition of stabilized nucleophiles (e.g., malonate anions) to q -naphthylpalladium complexes has been achieved [85]. [Pg.415]

Several other mechanistically distinct metal-catalyzed dearomatization procedures have been reported, and almost all involve phenol or naphthol derivatives undergoing dearomatization via intramolecular transformations. Intramolecular Pd- and Rh-catalyzed C4-arylation and alkylation of /)ara-substituted phenols has been used to construct compounds of general structure 82 (Fig. 15.1) [86]. These reactions rely on generation of electrophilic aryl or alkyl o-metal complex intermediates that participate in tandem C4 metalation-reductive elimination with an attached phenol. Ruthenium- and Pt-catalyzed reactions of naphthalenes and alkynes deliver spirocyclic products such as 83 [87, 88]. An asymmetric intramolecular naphthalene dearomatization catalyzed by Pd(0)-phosphine complexes has been used to prepare carbazole derivatives 84 in good enantiomeric excess from l-(AI-2-bromophenyl)aminonaphthalene precursors [89]. [Pg.415]

The reaction of pyridines with organolithium reagents afforded mainly 2-substituted pyridines through alkyl addition to generate a dearomatized hthium complex of dUiydropyridine. From this species, it has been though that ehmination of highly insoluble lithium hydride would yield the final... [Pg.52]

Reaction scope Despite attempts to date to achieve a dearomatization and hydrosilylation of heteroaromatics with magnesium catalysts faiUng to achieve turnover, the hydroboration of pyridine and alkyl and aryl substituted pyridines along with quinoline and isoquinoline with pinacol-borane catalyzed by 5-10 mol% [((ArNCMe)2CH Mg"Bu] has been reported (Scheme 18) [126]. [Pg.222]


See other pages where Dearomatization reactions alkylative is mentioned: [Pg.401]    [Pg.32]    [Pg.407]    [Pg.405]    [Pg.255]    [Pg.142]    [Pg.71]    [Pg.94]    [Pg.94]    [Pg.152]    [Pg.402]    [Pg.412]    [Pg.26]    [Pg.54]    [Pg.224]    [Pg.48]    [Pg.52]    [Pg.55]    [Pg.197]    [Pg.825]    [Pg.457]   


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Dearomatization reactions

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