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Halenaquinol, asymmetric Heck reaction

In a related study, the Shibasaki group examined cyclizadon of naphthyl triflate 10.1 (Scheme 8G.10) [23], Cyclization of 10.1 under standard cationic conditions gave Heck product 10.2 in 78% yield and 87% ee. Evidently, the reaction is fairly tolerant of the nature of the aryl group, because both 10.1 and 9.3 behaved similarly. An interesting variation of this reaction was also demonstrated in which Suzuki coupling and asymmetric Heck cyclization were performed in a one-pot operation. Thus, treatment of ditriflate 10.3 with borane 10.4 under standard Heck conditions provided 10.2 in similar enantioselectivity to the stepwise procedure, albeit in quite low yield. Heck product 10.2 was converted in several steps to the natural products, halenaqui-none (10.5) and halenaquinol (10.6). [Pg.682]

Catalytic asymmetric intramolecular Mizoroki-Heck reactions have been employed to synthesize several polyaromatic polyketide natural products. In one such endeavour, the catalytic asymmetric cyclization of alkenyl naphthyl triflate 84 was a central step in total syntheses of halenaquinone (88) and halenaquinol (89) recorded in the Shibasaki group laboratory (Scheme 16.19) [52]. Naphthyl triflate 84, which arose from Suzuki coupling of triflate 81 with alkylborane 82, was cyclized using the conditions that had become nearly... [Pg.546]

Alternatively, tetrahydroanthracene 85 was also obtained directly from symmetrical ditriflate 86 by a Suzuki cross-coupling/asymmetric Mizoroki-Heck cascade reaction. In this case, reaction of ditriflate 86 with alkylborane 82, Pd(OAc)2, (S)-BINAP and K2CO3 in THF at 60 °C directly gave product 85 in high enantiopurity, albeit in 20% yield. Although the yield for this one-pot conversion was poor, this transformation represents a novel application of the asymmetric Mizoroki-Heck cyclization and remains the only reported example of cascade Suzuki cross-coupling/asymmetric Mizoroki-Heck cyclization. A series of additional synthetic transformations was required to convert 85 to pentacyclic intermediate 87, which had earlier been converted by Harada et al. [53] to halenaquinone (88) and halenaquinol (89). [Pg.547]


See other pages where Halenaquinol, asymmetric Heck reaction is mentioned: [Pg.342]    [Pg.121]    [Pg.1237]    [Pg.566]    [Pg.1237]   
See also in sourсe #XX -- [ Pg.1303 ]




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