关键词： stereoselective reductions   hydrides   cyclization   asymmetric synthesis   piperidines  

摘要： The asymmetric synthesis of all four stereoisomers of 4-hydroxypipecolic acid (1) from the polyfunctionalized chiral building blocks delta -amino beta -keto esters (S-S,R)-(+)-5 or (R-S,S)-(-)-5 is described. Key steps in the synthesis are the stereoselective reductions of b-phenylpiperidine-2,4-dione (6) and N-sulfinyl delta -amino beta -keto esters 5 to cis 4-hydroxy 2-piperidinone 7 and syn-delta -amino beta -hydroxy ester 9, respectively. The only protecting/deprotecting group chemistry required is related to the oxidation step.

关键词： Thiols   Oxides   Enantioselective synthesis   Organophosphorus compounds   Rearrangement  

摘要： Diastereoselectivity of up to 88% was achieved for the synthesis of an alpha -mercapto gamma -unsaturated phosphonate using the readily available chiral dimenthylphosphonyl ester group and a carbanionic [2,3]-sigmatropic rearrangement, Absolute configuration of the newly formed chiral center of this nonracemic thiol was determined, and the corresponding phosphono thiolane and thiolane S-oxide were also stereoselectively prepared.

关键词： Amides   Anions   Nitrogen compounds   Stereoselectivity   Enantioselective synthesis  

摘要： The highly diastereoselective addition of lateral lithiated o-tolunitriles to sulfinimines followed by treatment of the resulting sulfinamide with MeLi, hydrolysis, and reduction represents a concise new methodology for the asymmetric synthesis of 1,3-disubstituted tetrahydroisoquinolines.

关键词： aldols   cycloadditions   cycloheptenes   polyketides   polyols  

摘要： A new approach to the asymmetric synthesis of pentadeca-1,3,5,7,9, 11,13,15-octols and their derivatives is presented. It is based on the Sharpless asymmetric dihydroxylation (AD) of 4,4'-methylene[(1R,1'S,6R,6'S)-6-acet-oxycyclohept-3-en-1-yl]bis(4-methoxy-benzoate) (9), derived from a double [3+4] cycloaddition of the 1,1,3-trichloro-2-oxyallyl cation with 2,2'-methylenedifuran (1). The diol (-)-10, obtained in 98.4% ee from 9 with "AD-mix-beta (5x ), was oxidised into (2R and 2S,6S,6R)-tetrahydro-2-hydroxy-6-{(4S,6S)-{6-hydroxy-4-[(4-methoxybenzoyl)oxy]cyclohept-1-en-1-yl}-2-oxopropyl)-2H-pyran-4-yl 4-methoxybenzoates ((-)-18). By the combinations of Evans' anti and Nasaraka's syn reductions of aldol (-)-18 with the double Mitsunobu reaction, 16 diastereomeric pentadeca-1,3,5,7,9,11,13,15-octols and analogues can be obtained, in principle, with high enantio- and diastereoselectivities.

关键词： Stereoselective total synthesis   Grandisol   Enantiomers   Cycloadditions  

摘要： A novel approach to the asymmetric synthesis of(+)-grandisol, (1R,2S)-isopropenyl-1-methylcyclobutaneethanol, involves the use of catalytic kinetic resolution of a primary allylic alcohol, [( 1RS,5SR)-5-methylbicyclo[3.2.0]hept-2-en-2-yl] methanol. The allylic alcohol is prepared in four steps from simple achiral materials involving the use of a modified Shapiro reaction. The resolved alcohol (95% eel is then reduced in two steps to the corresponding methyl alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene. This alkene is converted to (+)-grandisol (95% eel, in three steps, by modified literature procedures.

关键词： 抗肿瘤药/化学合成   多孔动物门/化学   动物  

摘要： [GRAPHICS] A catalysis-based approach to the core region 24 of the antitumor agents salicylihalamides A and B is reported. Key steps are two asymmetric hydrogenations of beta -keto esters 13 and 16 catalyzed by [(R)-BINAP-RuCl2](2). NEt3 and an RCM-based macrocyclization effected by the NHC-containing ruthenium carbene 21. The stereochemical outcome of the tatter reaction is controlled by remote substituents on the phenolic OH group of the cyclization precursor 23.

关键词： 酶抑制剂/化学合成   自由基   马来酸酐类/化学合成   氧化还原   立体异构现象  

摘要： [GRAPHICS] The enantioselective construction of a fully functionalized core structure of (-)-CP-263,114 (1) containing most of the required functionality for total synthesis, was conducted through sequential radical fragmentation-reductive olefination.

关键词： Phase-transfer catalysis   Enantioselective synthesis   Diastereoselectivealkylation   Stereoselective synthesis   Chiral auxiliaries   Conjugate addition   Glycineequivalent   Efficient route   Aldol reactions   Derivatives  

摘要： New 1,5-dimethyl-4-phenylimidazolidin;2-one-derived acyclic chiral iminic glycine reagents have been prepared and diastereoselectively alkylated with activated alkyl halides and electrophilic olefins in the presence of lithium chloride under (a) strong bases (LHMDS, KOBut) and low temperature (-78 degreesC) conditions, (b) solid-liquid phase-transfer catalysis reaction (LiOH, TBAB;-20 degreesC) conditions, and (c) in the presence of organic bases (DBU, BEMP, TMG, -20 degreesC). In the case of dielectrophiles C- and N-alkylation tabs place to afford heterocyclic derivatives. Hydrolysis bf alkylated products has been carried out (a) in two-step procedures with LiOOH or LiOH followed by acidic hydrolysis or Dowex purification, (b) in one single-step under refluxing water to give the corresponding alpha -amino acid, (c) in the presence of DBU in methanol to provide N-protected alpha -amino acids methyl esters, or (d) by a protection-hydrolysis procedure to afford N-Boc-protected alpha -amino acids. The chiral imidazolidinone has generally been recovered in good yield. This methodology has been shown to be useful for the synthesis of acyclic and heterocyclic (S)- and (R)-alpha -amino acids.

关键词： Stereoselective synthesis   Enantioselective synthesis   Aldol reactions   L-threonine   Derivatives   Vancomycin   (arylthio)nitrooxiranes   Aldehydes  

摘要： Describes the asymmetric synthesis of the beta-hydroxy alpha-amino acids, phenylserine and beta-hydroxyleucine, using the sulphinimine-mediated asymmetric Strecker synthesis. Synthesis schemes; Diastereoselectivies for the reactions.

关键词： Efficient formal synthesis   Stemodane diterpenes   End game   (+/-)-aphidicolin   Alcohols   (+)-aphidicolin   Alder   Hydroperoxide   Epoxidations   Conversion  

摘要： The 8-epiaphidicolane skeleton (3) was formed in one key reaction by highly diastereoselective tandem transannular Diels-Alder (TADA)-aldol reactions from the trans-trans-cis trienic macrocycle (4). The unnatural derivative (11R)-(-)-8-epi-11-hydroxyaphidicolin (2) was thus constructed, and an original solution to the C16 functionalization problem of many aphidicolin (1) syntheses is presented.