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ABSTRACT: The first asymmetric total syntheses of botcinins C (18), D (19), E (20), and F (21), botcinic acid (22), botcinic acid methyl ester (23), botcineric acid (26), and 3-O-acetylbotcinic acid methyl ester () were achieved. The structures of these compounds have been unequivocally determined through their total syntheses and those of 20, 22, 23, 26, and are identified with the revised forms of the natural products formerly assumed to be 2-epibotcinolide (10), botcinolide (6), 4-O-methylbotcinolide (7), homobotcinolide (11), and 3-O-acetyl-5-O-methylbotcinolide (8), respectively. It was further proved that the proposed nine-membered ring structure of 2-epibotcinolide (10) is very unstable and the ineluctable translactonization easily occurred to form the corresponding gamma-lactone .
Chemical Communications 02/2009; · 6.17 Impact Factor
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ABSTRACT: Stereoselective total synthesis of botcinins C, D, and F is effectively carried out through asymmetric aldol reactions, 6-endo ring closure, and SmI2-mediated 3,4-trans or -cis stereoselective intramolecular Reformatsky reaction. Rapid esterification of the main skeleton of botcinins with the chiral side chain using MNBA and DMAP produced botcinin D, an antifungal chemical against a pathogen of rice blast disease.
Organic Letters 08/2008; 10(14):3153-6. · 5.86 Impact Factor
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ABSTRACT: We have developed effective methods for the total synthesis of 2-hydroxytetracosanolide and 2-hydroxy-24-oxooctacosanolide, the defensive salivary secretions of termites. The former natural product isolated from Armitermes neotenicus, a species of termite that inhabits Guyana, contains a 25-membered lactone backbone, and the latter, extracted from Pseudacanthoterme springer, an African termite, includes a 29-membered lactone moiety. The key cyclization to produce the 25- or 29-membered lactone core is performed by using 2-methyl-6-nitrobenzoic anhydride (MNBA) with a stoichiometric amount of 4-(dimethylamino)pyridine (DMAP) or a catalytic amount of 4-(dimethylamino)pyridine N-oxide (DMAPO).
Chemistry - An Asian Journal 03/2008; 3(2):462-72. · 4.50 Impact Factor
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ABSTRACT: This protocol describes a procedure for the synthesis of a 29-membered macrolactone. The facile mixed-anhydride method is very effective for the preparation of carboxylic esters and lactones using substituted benzoic anhydrides by the promotion of Lewis acid or basic catalysts under mild reaction conditions. Owing to the reaction rapidly proceeding to produce the monomeric compounds with high chemoselectivity, the protocol is quite powerful for the synthesis of not only the giant-sized lactones but also the highly strained cyclic compounds such as medium-sized lactones. The remarkable efficiency of the lactonizations promoted by the substituted benzoic anhydrides has been already shown in the synthesis of many natural complex molecules. It takes approximately 19 h to complete the protocol: 0.5 h to set up the reaction, 13.5 h for the reaction and 5 h for isolation and purification.
Nature Protocol 02/2007; 2(10):2312-7. · 8.36 Impact Factor
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ABSTRACT: [Structure: see text] The total synthesis of pseudo 2-epibotcinolide (1b) through several featured synthetic approaches has been attained. First, the chiral linear precursors of the nine-membered ring compound is stereoselectively constructed by the asymmetric aldol reaction for producing beta-hydroxy ester units. Second, the key cyclization reaction to form the nine-membered lactone moiety is efficiently achieved by the extremely facile and powerful mixed-anhydride method promoted by 2-methyl-6-nitrobenzoic anhydride (MNBA) with basic promoters.
Organic Letters 12/2006; 8(23):5279-82. · 5.86 Impact Factor
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ABSTRACT: Various 1,1-difluoro-1-alkenes such as monosubstituted 1,1-difluoro-1-alkenes, 2-bromo-1,1-difluoro-1-alkenes, and 3,3-difluoroallylic alcohols are synthesized in two simple steps from 1-trifluoromethylvinylsilane: (i) its SN2' reaction with nucleophiles to construct 2,2-difluorovinylsilanes and (ii) the subsequent substitution of electrophiles for the vinylic silyl group. The combination of these two processes allows a one-pot synthesis of the functionalized 1,1-difluoro-1-alkenes starting from 1-trifluoromethylvinylsilane, which functions as a CF2=C(-)-CH2+ synthon.
The Journal of Organic Chemistry 11/2003; 68(20):7800-5. · 4.45 Impact Factor
