- Total synthesis of (+)-crocacin A
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Total synthesis of the potent antifungal and cytotoxic agent (+)-crocacin A is described. The crucial (Z)-5,6-enoic amide moiety in this molecule was built by stereoselective partial reduction of a skipped diyne precursor. The diene, thus obtained, was transformed into a silyl epoxide that was regioselectively opened with an azide ion to furnish an α-azido-β-hydroxyalkylsilane intermediate. Peterson elimination of this β-hydroxysilane component in the final step resulted in the formation of the (Z)-8,9-enamide moiety of the molecule leading to a successful completion of its total synthesis.
- Chakraborty, Tushar K.,Laxman, Pasunoori
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p. 4989 - 4992
(2007/10/03)
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- Efficient asymmetric synthesis of biologically important tryptophan analogues via a palladium-mediated heteroannulation reaction
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A novel and concise synthesis of optically active tryptophan derivatives was developed via a palladium-catalyzed heteroannulation reaction of substituted o-iodoanilines with an internal alkyne. The required internal alkyne 14a or 25 was prepared in greater than 96% de via alkylation of the Schoellkopf chiral auxiliary 19 employing diphenyl phosphate as the leaving group. The Schoellkopf chiral auxiliary was chosen here for the preparation of L-tryptophans would be available from D-valine while the D-isomers required for natural product total synthesis would originate from the inexpensive L-valine (300-g scale). Applications of the palladium-catalyzed heteroannulation reaction were extended to the first asymmetric synthesis of L-isotryptophan 38 and L-benz[f]tryptophan 39. More importantly, the optically pure 6-methoxy-D-tryptophan 62 was prepared by this protocol on a large scale (>300 g). This should permit entry into many ring-A oxygenated indole alkaloids when coupled with the asymmetric Pictet-Spengler reaction. In addition, an improved total synthesis of tryprostatin A (9a) was accomplished in 43% overall yield employing this palladium-mediated process.
- Ma,Liu,Li,Flippen-Anderson,Yu,Cook
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p. 4525 - 4542
(2007/10/03)
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- Concise synthesis of optically active ring-A substituted tryptophans
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A concise synthesis of optically active tryptophan derivatives was developed via diastereoselective alkylation of the Schollkopf chiral auxiliary 4 to provide alkyne 2 which underwent palladium-catalyzed heteroannulation with iodoanilines 1 to furnish protected tryptophans 3. Hydrolysis and subsequent saponification of 3 provided the desired tryptophans 12 in good yields.
- Ma, Chunrong,Liu, Xiaoxiang,Yu, Shu,Zhao, Shuo,Cook, James M.
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p. 657 - 660
(2007/10/03)
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- Effect of the leaving group on the alkylation diastereoselectivity of the Schollkopf chiral auxiliary
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Tosylates, diphenylphosphates and bromides were employed to study the effect of the leaving group on the alkylation diastereoselectivity of the Schollkopf chiral auxiliary 1 at aliphatic, benzylic, propargylic and allylic electrophilic centers. The diastereoselectivity generally follows the pattern: diphenylphosphate > tosylate > bromide. In terms of both diastereoselectivity and yield, each leaving group possesses a different advantage.
- Ma, Chunrong,He, Xiaohui,Liu, Xiaoxiang,Yu, Shu,Zhao, Shuo,Cook, James M.
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p. 2917 - 2918
(2007/10/03)
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- Preparation of 2-iodo-1,3-butadienes from 1-trimethylsilyl-2,3- butadienes and their functionalizations
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Successive treatment of 1-trimethylsilyl-2.3-butadienes with iodine and tetra-n-butylammonium fluoride in the same flask affords 2-iodo-1.3- butadienes in good yields and their palladium-catalyzed carbonylation and alkynylation allows introduction of este
- Nishiyama, Takashi,Esumi, Tomoyuki,Iwabuchi, Yoshiharu,Irie, Hiroshi,Hatakeyama, Susumi
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- Practical and Safe Sulfonylation of 2-Alkynyl and 2-Alkenyl Alcohols Using the Combined Bases of a Catalytic Amount of Tertiary Amine and Potassium Carbonate
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Several 2-alkynyl and 2-alkenyl alcohols were effectively sulfonylated with methanesulfonyl chloride or p-toluenesulfonyl chloride using the combined bases of a catalytic amount of tertiary amine and potassium carbonate.The reaction was conducted with reliable safety and while avoiding the disposal of wasted amines.The mesylation of 2-propyn-1-ol proceeded on a large scale (more than 20 kg) without a substantial production of explosive 3-chloro-1-propyne.The choice of the catalysts was important, and sterically unhindered tertiary amines, such as trimethylamine, N,N-d imethylbenzylamine, and triethylamine, were effective.Without these catalysts the reactions were significantly retarded.The reaction was so mild that it could be applied to complex and optically active 4-hydroxy-3-methyl-2-(2-propynyl)-2-cyclopenten-1-one, which is an important alcohol moiety of synthetic pyrethroids.
- Tanabe, Yoo,Yamamoto, Hitomi,Yoshida, Yoshihiro,Miyawaki, Takashi,Utsumi, Naoka
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p. 297 - 300
(2007/10/02)
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- Synthesis of Deuterium Labeled Polyunsaturated Fatty Acids
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Compounds containing carbon-carbon double bonds bearing cis deuterium atoms can be prepared conveniently by treating disubstituted acetylenes with bis(2-deuteriocyclohexyl)borane-B-D1 followed by reaction with CH3CO2D.As an example, the preparation of labeled linolenic acid is reported.
- Svatos, Ales,Attygalle, Athula B.,Meinwald, Jerrold
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p. 9497 - 9500
(2007/10/02)
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