关键词： ALLYLIC SUBSTITUTION   ENANTIOSELECTIVE CATALYSIS   CHIRAL LIGANDS   SOLID-STATE   HEXAFLUOROPHOSPHATES   ALKYLATION   PHOSPHINOARYLOXAZOLINES   AMINATION  

摘要： The novel chiral P,N-ligand 2-[2-(diphenylphosphino)phenyl]-5,6-dihydro-4-phenyl-4H-1,3-oxazine (4) was synthesized. The corresponding {dihydro[(phosphino-xP)aryl]oxazine-xN} (eta(3)-diphenylallyl)palladium(II) hexafluorophosphate 5 and the analogous [Pd(eta(3)-1,3-dimethylallyl)] complex 6 were investigated by X-ray analysis and 1D- and 2D-NMR spectroscopy. The complex 5 exists as 'exo'-syn-syn isomer in the solid state (Fig. 1). In solution, the same isomer exceeds with 90%. The X-ray crystal structure of 6 reveals that the dihydro(phosphinoaryl)oxazine ligand coordinates in a pseudo-enantiomeric conformation compared with that of 5 (Fig. 3). A syn-anti arrangement of the allyl substituents of 6 is favored in the solid state. H-1-NMR Spectroscopic investigations suggest that the auxiliary 6 adopts two conformations. This conformational instability together with 'exo'/'endo' and syn/anti isomerization leads to the formation of 6 isomers (Fig. 4). The asymmetric allylic substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate in the presence of 4 proceeds with a selectivity of 99% ee. The ee induced by 4 in the catalytic allylic substitution BE 1-methylbut-2-enyl acetate is moderate (54%).

关键词： b-内酰胺   不对称合成   手性  

摘要： 介绍了不对称合成b -内酰胺的研究进展,详细讨论了手性b-内酰胺的合成方法.

关键词： alkaloids   amino acids   hydrogenation   ruthenium  

摘要： The enantioselective ruthenium promoted hydrogenation of beta-keto ester, derived from (S)- or (R)-proline and (S)-pipecolic acid, provided a new efficient route to hydroxylated pyrrolizidine or indolizidine ring systems in diastereomeric excesses up to 99%. A practical synthesis of (+)-alpha-conhydrine is also reported. (C) 2000 Wiley-Liss,Inc.

关键词： asymmetric synthesis   chiral auxiliaries   Michael additions   phosphonic acids   TADDOLs  

摘要： Asymmetric C-P bond formation through phospha-analogous Michael addition to nitroalkenes leads with high asymmetric induction to α-substituted β-nitrophosphonic acids [Eq.(1)], which constitute valuable bifunctional synthetic building blocks and direct precursors to β-aminophosphonic acids. The key to success is a P nucleophile based on an easily removable TADDOL auxiliary.

关键词： SAMP hydrazones   alpha-alkylation   hydrazone cleavage   ketone reduction   mono-protected cyclohexanediones   asymmetric synthesis  

摘要： Alkylation of 1,4-cyclohexanedione monoethylene acetal SAMP-hydrazone with various electrophiles (10 examples given) and subsequent cleavage of the hydrazones with saturated oxalic acid furnished highly enantiomerically enriched alpha-alkylated mono-protected 1,4-cyclohexanedione derivatives in high yields and enantiomeric excesses of ee = 28, 80-greater than or equal to 99%. Reduction of the ketones gave the corresponding alcohols in good yields with high enantiomeric excesses (ee = 80-greater than or equal to 98%) and cis/trans-ratios of usually 85:15. (C) 2000 Wiley-Liss, Inc.

关键词： CYTOCHROME-P-450  

摘要： The asymmetric synthesis of the unlabeled and [D-8]-labeled terminal precursors, 4 ((-)-(S)-dihydroxyverbacine) and 19, respectively, in the biogenesis of the spermine alkaloids aphelandrine (5) and orantine (6), respectively, is described. A partial synthesis of the alkaloid (-)-(S)-[(E)-4-methoxycinnamoyl]buchnerine (10) is also presented.

关键词： Chiral auxiliary   azides   based   CYCLOADDUCT   geometry   Asymmetric synthesis   Cycloaddition Reaction   Nitrones   Phenylalanine  

摘要： The diastereomerically single chiral sulfonyl substituated isoxazolidine derivative (+)-(1) under bar (1) was prepared from L-phenylalanine via practical procedures. The acrylamide (-)-(2) under bar underwent dipolar cycloaddition reaction with nitrones and an azide with a high level of diastereoselectivity. The facial selectivity observed was consistent with the geometry optimized steric energies of the cycloadducts disclosed by MM2 calculations.

摘要： Triols containing three secondary hydroxy groups were reacted with either (i) toluene p-sulfonic acid or (ii) trimethylorthoacetate-pyridinium toluene p-sulfonate followed by toluene p-sulfonic acid.

关键词： alkynes   asymmetric synthesis   Baylis-Hillman reaction   camphor   titanium  

摘要： β -Substituted acrylates with high diastereomeric excess can be prepared by coupling optically active acetylenic ester titanium alkoxide complexes with aldehydes [Eq. (1); El=electrophile]. This reaction represents an asymmetric transformation complementary to the Baylis–Hillman reaction.

关键词： aldol reactions   antitumor agents   macrolides   natural products   total synthesis  

摘要： The total synthesis of the antitumor marine macrolide phorboxazole B (1) has been realized. The phorboxazoles are representative of a new structural class of macrolides and are maong the most cytostatic natural products known: inhibiting the growth of tumor cells at nanomolar concentrations. Key fragment couplings inlucde a highly selective double stereodiffentiating aldol reaction, a metalated-oxazole alkylation, and an oxazole-stabilized Wittig olefination. Following macrocyclization, a highly stereoseclective chelation-controlled addition of a side-chain alkenyl metal species provides the full carbon framework of phorboxazole B.