Asymmetric alkylation of aromatic aldehydes with dialkylzinc catalyzed by novel amino derivatives of hydroxytetrahydropyran

Novel, specially prepared, tetrahydropyran‐based γ‐amino alcohols (S)‐2‐(aminomethyl)‐3‐hydroxy‐6‐ethoxy(phenoxy)‐tetrahydropyrans ( I ) (amino = n‐Bu₂N, piperidinyl, pyrrolidinyl, azetidinyl) were tested as catalysts in the asymmetric addition of Et₂Zn and n‐Bu₂Zn to (hetero)aromatic aldehydes. In most cases the phenoxy derivatives of I acted more enantioselectively than the ethoxy ones. The dibutylamino derivaties showed the least enantioselectivity; the pyrrolidinyl derivatives were more active as catalysts than piperidinyl and azetidinyl compounds. The highest enantioselectivity was observed in the addition of Et₂Zn to benzaldehyde in the presence of (S)‐2‐(N‐pyrrolidinylmethyl)‐3‐hydroxy‐6‐phenoxytetrahydropyran. The corresponding alcohol was prepared with 72% ee (R‐configuration). The addition of dibutylzinc proceeded slowly and less selectively. The alkylation of (hetero)aromatic aldehydes with Et₂Zn and n‐Bu₂Zn was also studied in the presence of the known optical inductor (1S,2R)‐N,N‐dibutylnorephedrine. Some chiral aromatic secondary alcohols were synthesized in high chemical yields and up to 93% ee enantioselectivity. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis and Properties of Chiral Pyrazolidines Derived from (+)‐Pulegone

Several enantiomerically pure N(2)‐substituted octahydroindazoles were prepared as bicyclic pyrazolidine derivatives of (+)‐pulegone. Condensation of pulegone with hydrazine delivered a hexahydroindazole intermediate, which underwent N(2)‐substitution with various electrophiles (alkyl halides, acyl chlorides, phenyl isocyanate). The resulting N(2)‐substituted hexahydroindazoles could be reduced with LiBEt₃H in THF to the target compounds. In addition, a N(2)‐thiobenzoyl and some N(2)‐carbamoyl derivatives as well as a N(1)‐substituted octahydroindazole were synthesized. The compounds showed medium activity as iminium ion catalysts promoting quantitatively the Michael addition of nitroethane to cinnamaldehyde in up to 82 % ee for the resulting syn‐diastereoisomer and 78 % ee for the anti‐diastereoisomer. Unexpectedly, the N(2)‐acyloctahydroindazoles were readily oxidized under aerobic conditions. Moreover, it was shown that an oxidation of methyl phenyl sulfide to the corresponding sulfoxide is promoted by an N(2)‐acyloctahydroindazole in deuterochloroform as solvent. It is proposed that the oxidation of N(2)‐acyloctahydroindazoles proceeds by in situ generation of hydrogen peroxide, which in turn can act as an oxidant.     

Nickel‐Catalyzed Conjugate Addition of Silyl Ketene Imines to In Situ Generated Indol‐2‐ones: Highly Enantioselective Construction of Vicinal All‐Carbon Quaternary Stereocenters

The first enantioselective conjugate addition of silyl ketene imines to in situ generated indol‐2‐ones was performed in the presence of a chiral N ,N ′‐dioxide/Ni^II catalyst. This method provides efficient access to chiral β‐alkyl nitriles bearing congested vicinal all‐carbon quaternary stereocenters in up to 90 % yield with 23:1 d.r. and 98 % ee . The products enable facile transformations to chiral pyrroloindoline frameworks and spirocyclohexane oxindole derivatives. A possible transition state was also proposed to explain the origin of the asymmetric induction.     

Synthesis and Anti‐influenza Virus Activity of Novel bis(4H‐chromene‐3‐carbonitrile) Derivatives

An efficient and convenient method for the synthesis of bis(4H‐chromene‐3‐carbonitrile) derivatives by one‐pot, multicomponent reaction of bis‐aldehydes, malononitrile, and dimedone in the presence of a catalytic amount of piperidine is reported. Bis(2‐benzylidene‐1H‐indene)‐1,3‐(2H )‐dione derivatives were obtained as the main products as a result of reaction of the bis(arylidenemalononitriles) with indandione. The anti‐influenza H5N1 virus activities of the newly prepared bis‐chromene derivatives are also investigated.     

Metal‐Free Reaction of ortho‐Carbonylated Alkynyl‐Substituted Arylaldehydes with Common Amines: Selective Access to Functionalized Isoindolinone and Indenamine Derivatives

Herein we describe a reaction of ortho‐carbonylated alkynyl‐substituted arylaldehydes with common primary amines that can provide functionalized isoindolinone and 3‐hydroxylindenamine products in high yields. Depending on the substituent size of primary amines, two distinct reaction pathways were exploited selectively, that are, an initial aza‐conjugate addition followed by hydrogen transfer to access isoindolinone framework and a unique oxa‐conjugate addition followed by Petasis–Ferrier rearrangement to afford indenamine derivatives. In the presence of Et₃N, the reaction property of small primary amines was changed, proceeding to afford 3‐hydroxylindenamine derivatives efficiently. These products contain interesting substructures that exist in many natural products and bioactive molecules. The reaction features contain the use of transition‐metal‐free catalysts, simple operation, broad substrate scope, and product diversity.     

Copper(I)‐Catalyzed Amination of Halogenopyridines with Polyamines

Cu^I‐Catalyzed amination of 2‐bromo‐, and 2‐, 3‐, and 4‐iodopyridines with tri‐ and tetraamines aimed at the synthesis of N,N′‐diheteroaryl derivatives was studied. A strong dependence of the product yields on the nature of starting compounds and the ligand used was observed. The increase in the number of ethene‐1,2‐diamine fragments in the polyamine structure led to the increase in the yields of polyheteroarylated compounds, whereas propane‐1,3‐diamine fragments favored the formation of monopyridinyl derivatives and promoted the heteroarylation of the secondary amino groups. 2‐Iodopyridine, as a more reactive compound, readily formed N,N‐diarylated products. The best yields of the target N,N′‐dipyridin‐2‐yl derivatives were 76% in the case of the triamine and 68% in the case of the tetraamine. A comparison of Cu^I‐ and Pd⁰‐mediated heteroarylation of polyamines was also presented.     

Short Syntheses of some ‘Decalin‐1,8‐diones’ and their Derivatives: Breaking the Pretended Symmetry

A cheap synthesis of the so‐called ‘decalin‐1,8‐diones’ started with the conjugate (1,4‐) addition of cyclohex‐2‐en‐1‐one derivatives to the γ‐position of the dilithium derivative (buta‐1,3‐diene‐1,1‐bis(olate)) of crotonic acid. Hydrogenation of these ‘1,4‐γ’ adducts and final cyclization afforded the enol tautomers of decalin‐1,8‐diones. Nucleophilic substitutions at these 3‐oxoenols by NH₃ or primary amines created only monoamino products (namely, 3‐oxoenamines) whose reactions with OPCl₃ yielded dihydro(1,3,2)oxazaphosphinin‐2‐one derivatives. The two regioisomers of a trimethyl‐3‐oxoenamine served as models for the constitutional assignments of the two rapidly interconverting (hence, individually NMR‐invisible), tautomeric trimethyl‐3‐oxoenols. Such methyl substitutions served to break the ‘pretended’ symmetry of ‘decalin‐1,8‐dione’. Hydrazine and 3‐oxoenols furnished oxygen‐free indazole derivatives whose N?H bonds exchanged with t_1/2=ca. 0.00035 s at ca. ?58(9) °C.     

Utility of Bis‐Hydrazonoyl Chlorides as Precursors for Synthesis of New Functionalized Bis‐Thiadiazoles as Potent Antimicrobial Agents

N′,N″‐([1,1’‐Biphenyl]‐4,4′‐diyl)bis(2‐oxopropanehydrazonoyl chloride) is considered to be the key intermediate for the synthesis of a variety bis‐1,3,4‐thiadiazole derivatives in one step methodology with good yields by reaction of with a series of hydrazinecarbodithioate derivatives 2a–e , 6a , b , and 8a–e . The assigned structures for all the newly synthesized compounds were confirmed on the basis of elemental analyses and spectral data (infrared, NMR, and mass), and the mechanisms of their formation were also discussed. Moreover, the antimicrobial activity for twelve selected products was screened, and the results obtained exploring the high potency of some of the tested compounds compared with the employed standard bactericides and fungicides. In addition, the minimum inhibitory concentration of the tested compounds was determined, and the results obtained exploring the high potency of three of the tested compounds against all the tested microorganisms.     

Metallations and Reactions with Electrophiles of 4‐Isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ) with N‐Allyl and N‐Propargyl Substituents: Chiral Homoenolate Reagents

N‐Allyl, N‐cinnamyl, and N‐(3‐trimethylsilyl)propargyl derivatives of 4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ) are prepared by lithiation of the parent DIOZ (with BuLi in THF) and reaction with the corresponding bromides (Scheme 1). Lithiation in the same solvent, with deprotonation by BuLi on the allylic or propargylic CH₂ group at dry‐ice temperature, provides colorful solutions, which are either combined with aldehydes or ketones directly or after addition (with or without warming) of (Me₂N)₃TiCl or (i‐PrO)₃TiCl. Conditions have thus been elaborated under which all three types of conjugated lithium compounds react in the γ‐position with respect to the oxazolidinone N‐atom: carbamoyl derivatives of enamines and allenyl amines are formed in yields ranging from 60 to 80% and with diastereoselectivities up to 98% (Schemes 2–5). The C=C bond of the N‐hydroxyalkenyl groups has (Z)‐configuration (products 5 and 8 ), the allene chirality axis has (M)‐configuration (products 9 ), and the addition to aldehydes and unsymmetrical ketones has taken place preferentially from the Si face. A mechanistic model is proposed that is compatible with the stereochemical outcome (assuming kinetic control and disregarding the presence of Li and Ti species in the reaction mixture; cf. L, M in Fig. 4). Hydrolysis of the enamine derivatives leads to lactols, oxidizable to γ‐lactones, with recovery of the crystalline oxazolidinone, as demonstrated in three cases (Scheme 6). Thus, the application of chiral oxazolidinone auxiliaries (cf. Figs. 1 and 2) has been extended to the overall enantioselective preparation of homoaldols.     

Benzimidazole Annulated New Heterocyclic Compounds: Synthesis of New Polycyclic Pyrazole Derivatives

Several ( 3 ) new benzimidazole based polycyclic compounds of potential pharmaceutical interest have been prepared starting from 2‐benzimidazolelyl (1,3‐dioxo‐2‐indenylidene) acetonitrile. Unhypothesized, the C≡N function of the plausible intermediates was released as HCN rather than a classical nucleophilic addition when treated with bidentate reagents such as hydrazines, 5‐amino‐1H‐1,2,4‐triazole, 5‐amino‐4‐cyano‐1H‐pyrazole and 2‐aminobenzimidazole. When compound 3 reacted with active acetonitrile derivatives it afforded new polyfunctional pyridines via elimination of HCN in addition to, new pyrimidine, pyrazine and azepine derivatives.     

Bifunctional‐Thiourea‐Catalyzed Diastereo‐ and Enantioselective Aza‐Henry Reaction

Bifunctional thiourea 1 a catalyzes aza‐Henry reaction of nitroalkanes with N‐Boc‐imines to give syn‐β‐nitroamines with good to high diastereo‐ and enantioselectivity. Apart from the catalyst, the reaction requires no additional reagents such as a Lewis acid or a Lewis base. The N‐protecting groups of the imines have a determining effect on the chirality of the products, that is, the reaction of N‐Boc‐imines gives R adducts as major products, whereas the same reaction of N‐phosphonoylimines furnishes the corresponding S adducts. Various types of nitroalkanes bearing aryl, alcohol, ether, and ester groups can be used as nucleophiles, providing access to a wide range of useful chiral building blocks in good yield and high enantiomeric excess. Synthetic versatility of the addition products is demonstrated by the transformation to chiral piperidine derivatives such as CP‐99,994.     

Homo‐ and copolymerization of norbornene derivatives with ethene by ansa‐fluorenylamidodimethyltitanium activated with methylaluminoxane

(t‐BuNSiMe₂Flu)TiMe₂ ( 1 ) activated with Me₃Al‐free methylaluminoxane (dried MAO) which conducts vinyl addition polymerization of norbornene (N) with very high activity was applied for homopolymerization of N derivatives (i.e., 5‐vinyl‐2‐norbornene (5V2N), 5‐ethylidene‐2‐norbornene (5E2N), dicyclopentadiene (DCPD)) at 40 °C. The activities for the N derivatives were about two orders of magnitude lower than that for N and decreased in the following order: 5E2N ? 5V2N ? DCPD. Copolymerization of ethene (E) and 5E2N under an atmospheric pressure of E was then conducted by 1 ‐dried MAO. The copolymerization proceeded with better activity than the homopolymerization of 5E2N and gave poly(E‐co‐5E2N) with narrow molecular weight distribution. The content of the ethylidene group in poly(E‐co‐5E2N) was controlled by the feed ratio of 5E2N/E. The T_g value of the copolymer changed from 70 °C to 155 °C according to the 5E2N content from 27 mol % to 68 mol %. The addition of N as a third monomer to the E‐5E2N copolymerization improved the activity and raised the T_g values of the terpolymer above 200 °C. The content of 5E2N was controlled by the 5E2N/N ratio with keeping the high T_g values. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4581–4587, 2007     

Regioselective synthesis and biological activity of oxidized chitosan derivatives

Oxidized chitosan derivatives with various degrees of oxidation (DS, 0.1–1.0) were prepared by the treatment of chitosan with CrO₃/aq HClO₄ or by the oxidation of ­3‐O‐ and N‐protected chitosan with 30% aq H₂O₂/Na₂WO₄ followed by 3‐O‐ and N‐deprotection. The oxidized products were then N‐acetylated with Ac₂O in order to improve their water‐solubility. Although the oxidized chitosan derivative of DS 0.28 and the degree of N‐acetylation of chitosan (DA) 38% was insoluble in the pH 3–8 region, that of DS 0.26 and DA 76% was soluble in the neutral pH range. The newly‐prepared acetylated and oxidized chitosan derivatives were found to suppress the chemiluminescence response of inflammatory cells such as canine polymorphonuclear cells (PMNs). Analysis by the surface plasmon resonance method revealed that the bind and release behavior of PMNs to acetylated oxidized chitosan derivatives was similar to that against carboxymethylated chitosan derivatives. The amount of water‐soluble chitosan derivative bound to cytokine IL‐8 was found to be affected by the structural and electronic features of the chitosan substituents in the chitosan chain. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of 2′‐Deoxy‐1′‐homo‐N‐nucleosides with Anti‐Influenza Activity by Catalytic Methyltrioxorhenium (MTO)/H2O2 Oxyfunctionalization

This paper describes a new route for the synthesis of 1′‐homo‐N‐nucleoside derivatives by means of either methyltrioxorhenium (MTO) or supported MTO catalysts, with H₂O₂ as the primary oxidant. Under these selective conditions, the oxyfunctionalization of the heterocyclic ring and the N heteroatom oxidation were operative processes, regardless of the type of substrate used, that is, purine or pyrimidine derivatives. In addition, the oxidation of 1′‐homo‐N‐thionucleosides, showed the occurrence of site‐specific oxidative nucleophilic substitutions of the heterocyclic ring. The MTO/H₂O₂ system showed, in general, high reactivity under both homogeneous and heterogeneous conditions, affording the final products with high conversion values of substrates and from medium to high yields. Many of the novel 1′‐homo‐N‐nucleoside analogues were active against the influenza A virus, without any cytotoxic effects, retaining their activity in both protected and unprotected forms.     

Synthesis of Chiral Vicinal Diamines by Silver(I)‐Catalyzed Enantioselective Aminolysis of N‐Tosylaziridines

The kinetic resolution of 2‐aryl‐N‐tosylaziridines and the asymmetric desymmetrization of meso ‐N‐tosylaziridines by ring openings with various primary and secondary anilines, and aliphatic amines as nucleophile have been realized by using a single silver(I)/chiral diphosphine complex as catalyst for the first time. The simple starting materials, broad scope, and easy scalability render this protocol a practical way to chiral vicinal diamine derivatives.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

Synthesis of New Chiral Derivatives of N,N′‐Dimethylpropyleneurea (DMPU) and Examination of Their Influence on the Regio‐ and Enantioselectivity of Addition of 2‐(1,3‐Dithianyl)lithium to Cyclohex‐2‐en‐1‐one

The preparation of three new chiral derivatives of DMPU (N,N′‐dimethylpropyleneurea) is described (Schemes 2–4); one type of derivative carries 1‐phenylethyl or 1‐cyclohexylethyl groups at the N‐atoms of the tetrahydropyrimidin‐2(1H)‐one ring ( 2 and 4 ), another type of derivative is substituted at C(4) and C(6) of the heterocyclic ring ( 7 ). The potential of these chiral Lewis bases as promoters in the regio‐ and/or enantioselective addition of 2‐(1,3‐dithianyl)lithium to cyclohex‐2‐en‐1‐one was explored; they are all unable to effect enantioselective addition; the derivatives with branched substituents at the N‐atoms do not shift the addition mode from 1,2 to 1,4, while the 3,4,5,6‐tetrahydro‐1,3,4,6‐tetramethylpyrimidin‐2(1H)‐one does (Scheme 5). The results provide useful information regarding the nature of the nucleophilic organolithium reagent: obviously, the steric hindrance to Li complexation on the CO O‐atom of the tetrahydropyrimidin‐2(1H)‐one by branched substituents at N‐atoms (cf. X‐ray crystal structure of 2 in the Fig.) prevents solvent‐separated‐ion‐pair (SSIP) formation; this was confirmed by PM3 and B3LYP/3‐21‐G(d)//PM3 calculations (Scheme 6).     

Synthesis of 4‐fluoroalkyl‐2H‐pyrido [1, 2‐a] pyrimidin‐2‐ones from 2, 2‐dihydropolyfluoroalkanoic acids

In the presence of N, N′‐dicyclohexylcarbodiimide, 2‐aminopyridine and its derivatives (2) condensed with 2, 2‐di‐hydropolyfluoroalkanoic adds (1) to give the corresponding amides. Subsequent intramolecular Micheal addition‐elimination reactions of the fluorine‐containing amides under basic conditions gave 4‐fluoroalkyl‐2H‐pyrido[1,2‐a]pyrimidin‐2‐ones (3) in good yields.     

A new series of liquid‐crystalline bi‐1,3,4‐oxadiazole derivatives: synthesis and mesomorphic behaviour

Symmetrical bi‐1,3,4‐oxadiazole derivatives, namely 5,5′‐bis(phenyl 4‐alkoxybenzoate)‐2,2′‐bi‐1,3,4‐oxadiazole (BBOXD‐n, n = 6, 10, 14, 16), were synthesised. All BBOXD‐n exhibited remarkably stable SmC phases by virtue of the high transition enthalpies of SmC–I. In addition, BBOXD‐6 and BBOXD‐10 showed an enantiotropic nemetic phase with enthalpies of the N–I transition up to 5.16 kJ mol^?1. As confirmed by wide‐angle X‐ray diffraction analysis and MM2, molecules of BBOXD‐n showed high‐angle tilting (55–57°) within their smectic C phases.     

Geometry‐Retentive C‐Alkenylation of Lithiated α‐Aminonitriles: Quaternary α‐Alkenyl Amino Acids and Hydantoins

α‐Amino nitriles tethered to alkenes through a urea linkage undergo intramolecular C‐alkenylation on treatment with base by attack of the lithionitrile derivatives on the N′‐alkenyl group. A geometry‐retentive alkene shift affords stereospecifically the E or Z isomer of the 5‐alkenyl‐4‐iminohydantoin products from the corresponding starting E ‐ or Z ‐N ′‐alkenyl urea, each of which may be formed from the same N ‐allyl precursor by stereodivergent alkene isomerization. The reaction, formally a nucleophilic substitution at an sp² carbon atom, allows the direct regioselective incorporation of mono‐, di‐, tri‐, and tetrasubstituted olefins at the α‐carbon of amino acid derivatives. The initially formed 5‐alkenyl iminohydantoins may be hydrolyzed and oxidatively deprotected to yield hydantoins and unsaturated α‐quaternary amino acids.