Diastereoselective Synthesis of Highly Functionalized Proline Derivatives

An efficient way to access highly functionalized proline derivatives was developed based on a Cu(I)-catalyzed reaction between CF₃-substituted allenynes and tosylazide, which involved a cascade of [3 + 2]-cycloaddition/ketenimine and a rearrangement/Alder-ene cyclization to afford the new proline framework with a high diastereoselectivity.     

A New and Diastereoselective Synthesis of Threo-Aryl-2-Piperidylmethanol Derivatives

A diastereoselective synthesis of threo-aryl-2-piperidyl- and aryl-1,2,3,6-tetrahydro-2-pyridylmethanol derivatives is described. The stereochemistry is controlled by intramolecularly assisted NaBH₄ reduction of the intermediate carbamates 3.     

Palladium(II)-Catalyzed Enantio- and Diastereoselective Synthesis of Pyrrolidine Derivatives

A palladium-catalyzed enantio- and diastereoselective synthesis of pyrrolidine derivatives is described. Initial intramolecular nucleopalladation of the tethered protected amine forms the pyrrolidine moiety and a quinone methide intermediate. A second nucleophile adds intermolecularly to afford diverse products in high enantio- and diastereoselectivity.     

Metalated 2-Alkenylsulfoximides in Asymmetric Synthesis: Diastereoselective Preparation of Highly Substituted Pyrrolidine Derivatives

Thanks to a productive interaction between reagent and substrate control, 2-alkenylsulfoximides 1 react to provide highly substituted pyrrolidine derivatives 2 enantiomerically pure and with defined absolute configuration at the newly formed stereogenic centers. Tol=tolyl, BOC=tert-butoxycarbonyl.     

Diastereoselective Synthesis of Benzoxanthenones

An oxidative catalytic vanadium(V) system was developed to access the naturally nonabundant diastereomers of carpanone from the corresponding alkenyl phenol monomer in one pot by tandem oxidation, oxidative coupling, and 4+2 cyclization. This system was applied to the synthesis of two other analogues of carpanone. Mild oxidizing silver salts were used as the terminal oxidant to minimize background oxidation which produces the natural diastereomer of carpanone. Further, the first examples of enantioselective oxidative benzoxanthenone formation are reported. Solvent polarity has a strong effect on enantioselectivity, consistent with a mechanism involving binding of vanadium Schiff base catalysts to the alcoholic moiety of the alkenyl phenols during the cyclization step.     

Diastereoselective Addition of Organozinc Reagents to Benzaldiminetricarbonylchromium Derivatives

Abstract

The reaction of benzaldiminetricarbonylchromium derivatives with benzylzinc bromide or allylzinc bromide in the presence of BF₃ · Et₂ O gave the corresponding amine complexes with high diastereoselectivities.     

Diastereoselective Synthesis of New Dialkylphosphorylhydrazones

A series of 22 dialkylphosphorylydrazones (dialkyl ester, N′-[(1E)-(R₁ phenyl)methylene]-phosphorohydrazidic acid), 20 of them new, along with three new N,N′-bis (diisobutylphosphorylthioamide)diamines (bis-[diisobutyl ester), N-thioxomethylene]-, diamine)phosphora-midic acid, were prepared and characterized by IR, ¹H NMR, ¹³C NMR, ³¹P NMR, and mass spectrometry. The analysis of ¹H NMR, ¹³C NMR, ³¹P NMR, and NOE spectra confirmed the observation of the single diastereoisomer E in the synthesis of dialkylphosphorylydrazones. The results of a molecular modeling study performed in order to investigate the mechanism of the synthesis of dialkylphosphorylydrazones are in agreement with the experimental results, i.e., the favored formation of diastereoisomer E over Z.     

Diastereoselective Radical Reactions Starting from Cyclic Iodohydrin Derivatives

The stereoselectivity of radical reactions using cyclic iodohydrins and 2-alkoxy iodides was investigated on a simple model system obtained from indene (see 1a ? d ). The low level of stereoselectivity inherent to this type of systems could neither be overcome by using large protective group on the O-atom of 1c nor by complexation with Lewis acids. However, starting from the free alcohol 1c , it was possible to obtain very high selectivities (trans/cis > 100:1) by forming an aluminium alkoxide derivative upon treatment with methylaluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) before running the radical reaction. Despite the high steric demand of these complexes, the reactions gave satisfactory yields even for the formation of C? C bonds.     

新型螺环苯并呋喃酮-六氢山酮素-吡啶类化合物的非对映选择性合成

以苯并呋喃酮-色酮合成子与吡啶查尔酮为原料,在DBU催化下,在二氯甲烷中发生Michael/Michael加成关环反应,非对映选择性合成了11个未见文献报道的螺环苯并呋喃酮-六氢山酮素-吡啶类化合物（3a~3k）,产率为46%~65%, dr值为6/1~11/1,其结构经¹H NMR, ¹³C NMR和HR-MS（ESI-TOF）表征,并进一步通过单晶 确定化合物3g的相对构型。结果表明：该类化合物含有连续5个立体中心,以及一个具有潜在生物活性的六氢山酮素骨架和苯并呋喃酮骨架,可以为生物活性筛选提供物质基础。      

Facile Diastereoselective Synthesis of Carbohydrate-Based Thiochromans

An efficient and novel diastereoselective thiochroman synthesis using the carbohydrate chiral pool via intramolecular Friedel-Crafts alkylation is presented. The scope and limitations of the method are investigated.     

反式2,3-二芳基取代-1-氨基环丙烷羧酸的合成及其结构研究

芳香醛与马尿酸在Erlenmeyer反应条件下缩合得到(Z)-2-苯基4芳亚甲基-5(4H)-噁唑酮,然后在室温下与芳基重氮甲烷通过非对映高立体选择性1,3-偶极环加成反应得到螺环化合物,再经醇解开环、水解去保护合成出反式2,3-二芳基-1-氨基取代环丙烷羧酸．通过元素分析,IR,^1H NMR,^13C NMR,MS和X射线晶体测定,确认了它们的化学结构和立体构型．实验结果表明,通过选择适当的芳香醛和芳基重氮甲烷,可以得到不同立体构型的反式2,3-二芳基取代-1-氨基环丙烷羧酸．     

A Diastereoselective Synthesis of Novel Multifunctional Thianes

The reaction of 2,2′-thiobis(1,3-diarylprop-2-en-1-ones) with malononitrile in the presence of sodium ethoxide under both thermal and solvent-free microwave conditions afforded a series of hitherto unknown 2e,6e-diaroyl-3e,5e-diaryl-4,4-dicyanothianes diastereoselectively in good yields via a double Michael addition. The structures of all the compounds have been elucidated by IR, ¹H NMR, ¹³C NMR, and elemental analysis.     

N-Alkoxyl Templates for Diastereoselective Pyrrolidine Synthesis

Intramolecular cyclization of N-alkoxyl amines are studied for the stereoselective preparation of 2, 4-disubstituted pyrrolidine derivatives. Reduction of oximes under acidic conditions by NaBH3CN afforded the corresponding nucleophilic hydroxylamine derivatives,which subsequently cyclized via SN2‘ mechanism to give the desired N-alkoxyl pyrrolidines.     

First and Highly Diastereoselective Synthesis of Palladepanes

Unexpected stability is observed for the palladacycloheptane rac-2, which is obtained as major product and single diastereomer from the cyclization of 1 and Pd(0). Up to a temperature of 50 degrees C 2 shows neither reductive elimination nor intramolecular insertion of another olefin.