关键词： ACETAL resins   LEWIS acids  

摘要： A streamlined and high-yielding synthesis of aprepitant (1), a potent substance P (SP) receptor antagonist, is described. The enantiopure oxazinone 16 starting material was synthesized via a novel crystallization-induced dynamic resolution process. Conversion of 16 to the penultimate intermediate cis-sec-amine 9 features a highly stereoselective Lewis acid-catalyzed trans acetalization of chiral alcohol 3 with trichloroacetimidate 18 followed by inversion of the adjacent chiral center on the morpholine ring. The six-step process for the synthesis of 9 was accomplished in extremely high overall yield (81%) and with only two isolations.

关键词： Amino Acids   Environmental Temperature   Kinetics   Resolving power   dynamic   Cinchona Alkaloids   Room temperature   Asymmetric synthesis   wide-range   Catalysis  

摘要： A rapid, highly efficient and general dynamic kinetic resolution (DKR) of racemic alpha-aryl UNCAs with the dual-function catalysis of modified cinchona alkaloid was accomplished at room temperature. This DKR led to the development of a highly enantioselective catalytic method for the practical synthesis of a wide rang of alpha-aryl and alpha-heteroaryl amino acids in 89-92% ee and 86-95% yield from racemic UNCAs.

关键词： ANTIBIOTICS   ASYMMETRIC synthesis   LACTONES   HYDROGENATION  

摘要： An asymmetric synthesis of the antibiotic (+)-negamycin (1) has been achieved, starting from commercially available (5R,6S)-4-(benzyloxycarbonyl)-5,6-diphenyl-2,3,5,6-tetrahydro-4H-1,4-oxazin2-one (2). The synthesis involved the stabilized Wittig olefination of the lactone carbonyl group of 2 and subsequent asymmetric hydrogenation to generate the corresponding all-syn oxazine 4 with excellent diastereoselectivity. Conversion of 4 into beta-alkoxy imine 7 and subsequent CeCl3-promoted chelation-controlled allylation of 7 generated the corresponding homoallylamine 8 with good diatereoselectivity, which was readily converted into (+)-negamycin (1) in 25% overall yield over 11 steps.

关键词： Aldehydes   Alkynes   Dapsone   Methane   Molecular Structure   Organometallic Compounds   Propanols   Stereoisomerism   Sulfones   Support   Non-U.S. Gov't   Titanium  

摘要： A new method for the asymmetric synthesis of anti-configured homopropargylic alcohols 1 is described, which features the addition of chiral sulfonimidoyl substituted bis(allyl)titanium complexes 3 to aldehydes, the methylation of sulfonimidoyl substituted homoallylic alcohols 2 at the N-atom, and the elimination of alkenyl (dimethylamino)sulfoxonium salts 7 with LiN(H)tBu. The reaction of isopropyl, cyclohexyl, and methyl substituted allylic titanium complexes 3a-c with benzaldehyde, p-bromobenzaldehyde, p-chlorobenzaldehyde, p-methoxybenzaldehyde, (E)-3-phenylpropenal, and phenylpropynal afforded with high regio- and diastereoselectivities the anti-configured sulfonimidoyl substituted homoallylic alcohols 2a-j, respectively. Only one allylic unit of the titanium complexes 3a-c was transferred in the case of unsaturated aldehydes, and the starting allylic sulfoximines 2a-g were recovered in approximately 50% yield. The methylation of the silyl protected alkenyl sulfoximines 6a-j with Me3OBF4 gave in practically quantitative yields the (dimethylamino)sulfoxonium salts 7a-j, respectively. Salts 7a-e, 7g, 7h, and 7j delivered upon treatment with 2 equiv of LiN(H)tBu the enantio- and diastereomerically pure saturated and unsaturated alkynes 9a-e, 9g, 9h, and 9j, respectively, in high yields. Besides the alkynes the sulfinamide 8 (96% ee) was isolated. Aminosulfoxonium salts 9f and 9i, which carry a CC triple bond, also suffered an elimination under these conditions but did not yield the corresponding diynes. Elimination of salts 7a-e, 7g, 7h, and 7j proceeds most likely through deprotonation at the alpha-position with formation of the novel alkylidenecarbene aminosulfoxonium ylides 19a-e, 19g, 19h, and 19j, respectively. The ylides 19a-e, 19g, 19h, and 19j presumably eliminate sulfinamide 8 with generation of the chiral nonracemic (beta-siloxyalkylidene)carbenes 20a-e, 20g, 20h, and 20j, which suffer a 1,2-H-shift with formation of alkynes 9. Support for the formation o

关键词： 3-(对氯苯基)-3-苯基丙酸   合成   不对称性   旋光活性  

摘要： 利用旋光活性的 (-)薄荷酮与丙二酸缩合制备了丙二酸亚 (5′-甲基 -2′-异丙基环己 )酯。然后与对氯苯甲醛进行Knovenagel缩合。缩合产物进一步与Grignard试剂发生Michael加成 ,加成产物经水解提供了一种 3 -(对氯苯基 ) -3 -苯基丙酸的不对称合成的新方法。

关键词： amines   alkylation   asymmetric synthesis   dendrimers   imines  

摘要： The enantioselective addition of dialkylzinc compounds to N-(diphenylphosphinyl)imines by using chiral dendrimers with flexible carbosilane backbones gives enantiomerically enriched N-(diphenylphosphinyl)amines with up to 92% ee. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

关键词： TRYPTOPHAN   CATALYSIS   ORGANIC synthesis (Chemistry)   INDOLE  

摘要： Tryptophan 1 (Trp) is superior to all other naturally occurring peptide residues in its ability to bind cations (the cation-a interaction). In an effort to expand the toolbox of Trp-like amino acids, in this note we report catalytic asymmetric syntheses of Trp regioisomers 2a-e, where the alanine unit is attached not to C-3 of indole but to C-2, C-4, C-5, C-6, or C-7. Excellent asymmetric induction is obtained in each case (generally >97% ee). Ab initio calculations suggest that the indole nuclei of 2a-e will bind Na+ with the same affinity as that of Trp.

关键词： ORGANIC synthesis (Chemistry)   CYCLOHEXANE   ESTERS   CRYSTALLIZATION  

摘要： An efficient asymmetric synthesis of 1,2,3-trisubstituted cyclopentanes and cyclohexanes is described. Three methods were developed for the preparation of the 2,3-disubstituted cyclopentenones and cyclohexenones, which are key achiral building blocks. These intermediates are reduced catalytically with (R)-2-methyloxazaborolidine in high yield (82-98%) and excellent ee (89-96%). Directed reduction of the chiral allylic alcohols using Red-Al gives exclusively the 1,2-anti stereochemistry (> 99:1). Epimerization of the ester center followed by saponification/crystallization affords the desired hydroxyacids in good yield (65-70%) and in high enantiomeric excess (> 99%).

关键词： LACTONES   PYROPHOSPHATES   METATHESIS (Chemistry)  

摘要： An alpha-phosphono lactone derivative of farnesol has been prepared, in both racemic and nonracemic forms, to provide a new type of farnesyl pyrophosphate analogue. Attempted preparation of the racemic alpha-phosphono lactone through rearrangement of a vinyl phosphate derived from the parent lactone resulted in both rearrangement and lactone ring opening, revealing that the farnesyl lactone was not stable to the excess of strong base required for the rearrangement. A procedure for C-P bond formation based on generation of the lactone enolate, reaction with a P(III) reagent, and oxidation was successful in providing the racemic alpha-phosphono lactone, in part, because only 1 equiv of strong base was required. The same strategy for phosphonate synthesis then was applied to the nonracemic farnesyl lactone, prepared through a sequence including allylation of farnesal with a nonracemic borane reagent, reaction of the product alcohol with acryloyl chloride, and formation of an unsaturated lactone through ring-closing metathesis. A similar strategy gave the corresponding racemic alpha-phosphono lactam through a six-step sequence from farnesal.