Intramolecular Nicholas reaction: stereoselective synthesis of 5-alkynylproline derivatives

The intramolecular Nicholas reaction of propargylic alcohols derived from N, N-acyl-diprotected omega-semialdehydes obtained from glutamic acid provided stereoselectively 5-alkynylproline derivatives. The suitable choice of the N-protecting group (tosyl or benzoyl derivative) permitted control of the stereochemistry during the ring formation. Semiempirical calculations of the species involved in the cyclization support the observed stereochemistry.     

Convergent stereoselective and efficient synthesis of furanic-steroid derivatives

The stereoselective synthesis of furanic-steroid derivatives involving ring-closing metathesis and catalytic hydrogenation as key steps is described. The synthetic strategy was first illustrated by the synthesis of the furanic-estrane derivative 1 in seven steps starting from estrone and 2-methylene-propane-1,3-diol. This compound initially targeted as a potential inhibitor of 17β-hydroxysteroid dehydrogenase type 1 by a docking experiment was found to inhibit the enzyme. The scope of this new strategy was also extended to furanic-androstane derivatives by synthesizing compound 20.     

One-pot stereoselective synthesis of 1,2-amino alcohol derivatives

Common β-hydroxy amino acids (such as threonine) can be readily transformed into 1,2-amino alcohols with excellent stereoselectivity. This one-pot decarboxylation-alkylation process allows the replacement of the carboxyl group by alkyl, allyl, or aryl groups, generally in high yields. A variation of the process (decarboxylation-Diels-Alder) allows the formation of bi- and polycyclic systems, which are useful precursors of alkaloid cores or iminosugars.     

First highly stereoselective synthesis of anti-alpha-trifluoromethyl-beta-amino acid derivatives

The Reformatsky-type reaction of 2-bromo-3,3,3-trifluoropropanoic imide with various types of imines, in the presence of ZnBr2 as a Lewis acid in THF at 0 degrees C for 3 h, gave the corresponding alpha-trifluoromethyl-beta-amino acid derivatives in a highly anti-selective manner.     

麻黄碱衍生噁唑烷类化合物的立体选择性合成

麻黄碱衍生噁唑烷类化合物是由麻黄生物碱和醛酮缩合而成的杂环化合物,它既比相应的麻黄碱碱性弱,脂溶性高,又比相应的醛、酮理化性质稳定,是比较有前途的麻黄碱类前体药物。我们利用麻黄生物碱和取代苯甲醛,立体选择性地合成出十一种噁唑烷类化合物(图1)。     

A short and stereoselective synthesis of functionalized pentenomycin derivatives

A short and stereoselective synthesis of 2-hydroxymethyl-4-deoxypentenomycin and 2-hydoxymethylpentenomycin derivatives is accomplished in five and seven steps starting from tetrabromonorbornyl derivatives in overall yields of 41% and 38%, respectively.     

Novel stereoselective synthesis of functionalized oxazolidinones from chiral aziridines

Enantiomerically pure N-(R)-alpha-methylbenzyl-4(R)-(chloromethyl)oxazolidinones (4R)-5a-k were synthesized in one step and high yields from various aziridine-2-methanols (S)-2a-k by intramolecular cyclization with phosgene. The alpha-methylbenzyl substituent on the nitrogen was easily cleaved to give both enanatiomers of 4-(chloromethyl)oxazolidinones (R)-7a and (S)-7a. (R)-7a was used for the efficient syntheses of (L)-homophenylalaninol analogues (S)-12a-j. We also applied the same methodology to prepare oxazolidinones 9a-c containing a heteroatom-substituted alkyl group at C-4 in high yields.     

Facile synthesis of 5-amino- and 7-amino-6-azaoxindole derivatives

An efficient approach for the formation of 5-amino- and 7-amino-6-azaoxindole derivatives was developed. 2-Amino-4-chloro-3-nitropyridine (8), and its 5-nitro-substituted regioisomer (9), respectively, were obtained by reaction with ethyl malonate. The resulting 2-amino-3/5-nitropyridine derivatives substituted in the 4-position with malonic acid diethyl ester (10, 11) were subjected to reductive cyclization yielding 3-ethoxycarbonyl-6-azaoxindole derivatives 4a and 5a. Protection of the amino function was not required. Intermediates 10 and 11 could also be converted to the corresponding 4-acetic acid ethyl esters 12 and 13 by dealkoxycarbonylation with LiCl, and subsequently cyclized under reductive conditions yielding 3-unsubstituted 5-/7-aminooxazindoles.     

Highly stereoselective synthesis of trisubstituted vinylcyclopropane derivatives via arsonium ylides

[reaction: see text] Alkylidene or arylidene malonates reacted with arsonium allylides to give trans-disubstituted cyclopropane-1,1-dicarboxylates with high stereoselectivity in high yields. The mechanism of the cyclopropanation reactions has also been investigated.     

Novel synthesis of 2,6-benzothiazonine derivatives

The reaction of 1-alkylamino-1-alkylthio-3-phenyl-3-thioxopropenes with phthaloyl chloride in toluene at 60°C, followed by treatment with triethylamine, afforded 6-alkyl-3-phenyl-2,6-benzothiazonine-1,5,7-triones in good to excellent yields.     

Highly regio- and stereoselective synthesis of tricyclic frameworks using Baylis-Hillman derivatives

A simple and convenient synthetic route for the synthesis of tricyclic chromeno[4,3-b]pyrrolidine frameworks using Baylis-Hillman bromides involving in situ formation of an imine, decarboxylation and a [3+2] cycloaddition sequence is described.     

Iminium ion cyclizations. Highly stereoselective synthesis of substituted tetrahydroisoquinoline derivatives

Cationic cyclizations of acyliminium ions $\text{2}$ (R₁  phenyl) occur with high stereo-selectivity, which is suggested to originate in the intermediate arenium ions.     

Highly regio- and stereoselective synthesis of indene derivatives via electrophilic cyclization

[reaction: see text] Indene or naphthalene derivatives are readily prepared in moderate to excellent yields with high regio- and stereoselectivity under very mild reaction conditions by the reaction of acetylenic malonates and ketones with I2, ICl, or NIS. The resulting iodides can be further elaborated using palladium-catalyzed coupling reactions.     

Organocatalytic sequential Michael reactions: stereoselective synthesis of multifunctionalized tetrahydroindan derivatives

Multifunctionalized tetrahydroindan derivatives with four stereocenters were constructed via two sequential Michael reactions between cyclic γ,δ-unsaturated-β-ketoester and nitroalkenes initiated with 0.5-2 mol % of cinchona alkaloid based bifunctional organocatalysts and then with 1 equiv of tetramethylguanidine for cyclization. The desired products could be obtained in high yields (up to 99% yield) with excellent enantioselectivities (95-99% ee) as well as diastereoselectivities (up to >99:1 dr) even on a gram scale.     

An efficient multicomponent protocol for the stereoselective synthesis of oxazinobenzothiazole derivatives

An easy and efficient protocol for the stereoselective one-pot synthesis of oxazinobenzothiazole derivatives is described.     

Novel stereoselective synthesis of 1,3-dienylsilanes via hydromagnesiation reaction of alkynylsilanes

Hydromagnesiation of alkynylsilanes gives (Z)-α-silylvinyl Grignard reagents, which undergo palladium-catalyzed cross-coupling reactions with alkenyl halides to afford stereoselectively 1,3-dienylsilanes in good yields.     

Novel transformation of 5-cyanouracil derivatives

5-Cyano-1-(dihydroxypropyl)-3-methyluracils were synthesized in the reaction of 1-(4-nitrophenyl)-5-cyano-3-methyluracil with appropriate aminodiols. In the aprotic solvents, the reaction proceeds according to the ANRORC type mechanism. In protic solvents the products of Dimroth rearrangement were isolated.