关键词： 1,3-cyclic sulfates   heterocyclisation   pyrrolidines   piperidines  

摘要： 1,3-Cyclic sulfates (1b-d) participate in heterocyclisation reactions to give pyrrolidines (2b) and piperidines (2c/d). Cyclic sulfate activation, when coupled to the enantio- and diastereoselective generation of 1,3-diols, provides a synthesis of (+)-sedridine (9).

关键词： 2-amino-2,6-dideoxy-galactose   neocarzinostatin   amino acid based synthesis   syn-aldol addition  

摘要： (+)-D-fucosamine and (+)-N-methyl-D-fucosamine (the amino sugar moiety of neocarzinostatin) have been synthesized from known building blocks derived from natural amino acids. Direct and diastereoselective construction of the key intermediate 4 was accomplished by a syn-aldol type reaction between Schollkopf's bislactim ether 2 and the 1,3-dioxolane-4-carboxaldehyde 3. Reduction and monomethylation of a O'Donnell's Schiff base derived from the common amino ester 7 allows an optional access to the N-methyl derivative.

摘要： Rhodium(II) carboxylate-catalyzed decomposition of 2-diazobutenoates in the presence of alkenes or dienes results in highly diastereo-selective cyclopropanations. Furthermore, these cyclopropanations occur with high asymmetric induction when using either α-hydroxy esters as chiral auxiliaries on the carbenoid, or chiral catalysts containing N-arylsulfonylprolinate ligands. These transformations can be used in general methods for the asymmetric synthesis of vinylcyclopropanes, cyclopropaneamino acids, 4,4-diarylbutanoates, cycloheptadienes, bicyclo[3.2.1]octadienes, 8-oxabicyclo[3.2.1]octan-3-ones, tropanes and other polycyclic compounds.

摘要： The use of pseudoephedrine as a practical chiral auxiliary for asymmetric synthesis is described. Both enantiomers of pseudoephedrine are inexpensive commodity chemicals and can be N-acylated in high yields to form tertiary amides. In the presence of lithium chloride, the enolates of the corresponding pseudoephedrine amides undergo highly diastereoselective alkylations with a wide range of alkyl halides to afford $\alpha$-substituted products in high yields. These products can then be transformed in a single operation into highly enantiomerically enriched carboxylic acids, alcohols, and aldehydes. Lithium amidotrihydroborate (LAB) is shown to be a powerful reductant for the selective reduction of tertiary amides in general and pseudoephedrine amides in particular to form primary alcohols.

关键词： 手性配体   合成   二醇   不对称合成   四芳基取代二醇  

摘要： 本文报道了由光学活性酒石酸出发，合成（４Ｒ，５Ｒ）－和（４Ｓ，５Ｓ）－２，２－二甲基－α，α，α＇，α＇－四芳基－１，３－二氧杂戌环－４，５－二甲醇配体（４）的方法（芳基：苯基，３，５－二甲苯基，１－条基，２－萘基）．手性配体都由红外光谱、核磁共振谱以及元素分析进行了结构确定．

摘要： In the presence of a catalytic amount (0.1-0.2 molar amount) of a 2-phenyl-1,3,2-oxazaborolidin-5-one, prepared by the reaction of dichlorophenylborane and N-(trifluoromethylsulfonyl)-L-phenylalanine, and enol silyl ethers ((R(2))(2)C=C(R(3))OTMS;R(3) = t-BuS, EtS, EtO, Ph) (1.1-1.5 molar amount), chiral cyclic acetals 6 derived from (R)-1,3-butanediol and aldehydes undergo an efficient ring-cleavage reaction with the inversion of the stereochemistry at the acetal carbon to give the anti isomer of the corresponding products with high stereoselectivity. The reaction is applicable to acetals derived from aromatic, aliphatic, and alpha,beta-unsaturated aldehydes. Not only enol silyl ethers, but also methallyltrimethylsilane and allyltributyltin, can be employed as nucleophiles, leading to the selective formation of the anti isomer of the corresponding allylated ring-cleavage products. Removal of the chiral auxiliary from these ring-cleavage products by a two-step sequence ((i) PCC (ii) Bn(2)NH(2)(CF3CO2)) furnishes enantiomerically enriched beta-hydroxy carbonyl compounds and homoallyl alcohols. A modest level of kinetic resolution is observed in the ring cleavage of a racemic acetal catalyzed by a phenylboron compound derived from N-mesyl-L-phenylalanine.

关键词： Enolates   Alcohols   Anions   Molecular structure   Post-translational modification  

摘要： Describes a general highly enantioselective synthetic route to substituted 2-azaspiro[3.5]nonan-1-ones. Previous methods for the synthesis of the compound; Reactivity of electrophiles at temperatures below -30 degrees centigrade; Experiments.

关键词： Reagents   Stereoselectivity   Enantioselective synthesis   Molecular structure   Selectivity  

摘要： Transmetalation of 1-lithiotetrahydroisoquinolyloxazolines with magnesium halides affords Grignard reagents that add to aldehydes with up to 80% selectivity for one of the four possible diastereomeric products. An oxazoline chiral auxiliary derived from camphor provides an optimal blend of diastereoselectivity and isomer separability. Synthetic applications of the optimal auxiliary, patterned after a literature approach in the racemic series, comprise an improved (formal) synthesis of bicuculline, egenine, and corytensine, as well as an efficient synthesis of corlumine. Preliminary NMR studies show that both 1-lithio- and 1-magnesiotetrahydroisoquinolyloxazolines are dynamic mixtures in THF solution at low temperatures. The barrier to pyramidal inversion of the secondary Grignard reagent is in the 9.8-10.1 kcal/mol range, while an upper limit of about 8.2 kcal/mol can be assigned to the barrier to the organolithium inversion.

关键词： Macrocyclic compounds   Enolates   Adducts   Anions   Electrophiles