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.     

Determination of Enantiomer Ratios of Bornane Congeners in Biological Samples Using Heart-Cut Multidimensional Gas Chromatography

The enantiomeric ratios of the chlorinated bornanes, 2-exo, 5,5,9,9,10, 10-heptachlorobornane (B[20030]-(022)), 2-endo,3-exo,5-endo,6-exo,8, 8,10,10-octachlorobornane (B[12012]-(202), Parlar No. 26), 2-exo,3-endo,6-endo,8,9,10,10-heptachlorobornane (B[21001]-(112)), 2,2,5,5,9,9, 10,10-octachlorobornane (B[30030]-(022), Parlar No. 38), 2-endo,3-exo,5-endo6-exo,8,8,9,10,10-nonachlorobornane (B[12012]-(212), Parlar No. 50), and 2,2,5,5,8,9,9,10,10-nonachlorobornane (B[30030]-(122), Parlar No. 62) were determined in a hake liver (Merluccius merluccius) and in two whitebeaked dolphin blubber (Lagenorynchus albirostris) samples. The analysis was performed by heart-cut multidimensional gas chromatography using an electron capture detector (ECD). Ultra 2 (5%-phenyl-95%-methylsilicone) was used as stationary phase in the first column and enantioselectivity was obtained in the second column with a phase consisting of a mixture of OV-1701 and heptakis(2,3,6-O-tert- butyldimethylsilyl)-β-cyclodextrin (10 : 1). All reference standards were also tested on the enantioselective column alone. The comparison of the two systems showed that deviations of ±0.12 from the racemic enantiomer ratio can be observed for the single column due to co-eluting impurities which are present in the reference standards. In most of the heart-cut chromatograms of the biota samples about 15 peaks could be found, showing the importance of a multidimensional separation system for an interference-free quantification by ECD. In all biological samples a significant deviation from the racemic enantiomer ratio was found for B[30030]-(022) (Parlar No. 38) and for B[30030]-(122) (Parlar No. 62). This indicates that an enantioselective disposition of the congeners occurs. In addition, considerations are presented concerning the relationship between congener structure and enantiomeric disposition.     

Synthesis of Optically Active α-Amino- phosphinic Acids by Catalytic Asymmetric Hydrogenation in Organic Solvents and Aqueous Micellar Media

Enantiomeric excesses of up to 99 % could be obtained in the synthesis of the biologically interesting acylated α-aminophosphinic acids 1 (R¹=Me, Ph; R²=H, Me, Et; R³=H, F, iPr) by asymmetric hydrogenation with rhodium complex catalysts and subsequent hydrolysis [Eq. (1)]. cod=1,5-cyclooctadiene.     

SYNTHESE UND STEREOCHEMIE DER 1-AMINO- UND 1-PHENYLAMINO-1,3-AZAPHOSPHOLAN-5-ONE

Abstract

Die Titelverbindungen werden durch Kondensation von Carboxymethyl- und 1-Carboxyethylphenylphosphin mit dem Hydrazon oder Phenylhydrazon des Benzaldehyds dargestellt. Die 1-Benzoylamino- und 1-Benzylidenamino-derivate des 1,3-Azaphospholan-5-ons sind auf unterschiedlichem Wege zugänglich, indem einmal das 1-Amino-1,3-azaphospholan-5-on mit Benzoylchlorid oder Benzaldehyd umgesetzt oder die Carboxyalkylphosphine mit N-Benzoyl-benzaldehydhydrazon bzw. Benzalazin zur Reaktion gebracht werden. Die Reaktionen verlaufen unter stark bevorzugter Bildung sterisch einheitlicher Diastereomere deren relative Konfiguration ¹H-NMR-spektroskopisch bestimmt wird. Vorstellungen über die Ursachen des stereospezifischen Reaktionsablaufs werden entwickelt.

The title compounds are prepared by condensation of carboxymethylphenylphosphine or 1-carboxyethylphenyl-phosphine with the hydrazone or phenylhydrazone of benzaldehyde. The 1-benzoylamino- and 1-benzylidenamino-derivatives of the basic compounds are made by two routes, by reaction of 1-amino-1,3-azaphospholan-5-ones with benzoylchloride or benzaldehyde or by interaction of the carboxyalkylphosphines with N-benzoyl-benzaldehyde-hydrazone or benzalazine, respectively. All the reactions proceed under stereospecific formation of certain diastereomers, the relative configuration of which is elucidated by investigating their ¹H-nmr-spectra. Suggestions concerning the stereospecifity of the reactions are discussed.     

On Penicillin‐Binding Protein 1b Affinity‐Labeling Reagents

The synthesis of some 3‐aryl‐3‐(trifluoromethyl)3H‐diazirine and benzophenone‐based photoaffinity labels is reported. The photolabile group is bound to a scaffold that also accommodates functional groups to which an indicator unit (biotin) and the bioactive ligand can be attached orthogonally. To three of the labels, moenomycin was conjugated with the aim to provide tools for the identification of the moenomycin binding site within the transglycosylase domain of the enzyme PBP 1b. Some preliminary photoaffinity‐labeling experiments were carried out.     

Systematic investigations of the photocatalytic alkyne-nitrile heterotrimerisation to pyridine

The photocatalytic heterocyclotrimerisation of ethyne and nitrile initiated by cobalt(I) complexes was studied. General mechanistic features as proposed for the ‘dark’ reaction were found to apply as well under photolytic conditions albeit with modifications. The results suggest that the irradiated light accelerates that stage of reaction, leading to the organometallic species which is believed to be the common intermediate for the formation of pyridine and benzene. The rate of pyridine production is linear dependent from nitrile concentration. Benzene formation may be minimised by keeping the ethyne concentration low. An alternative mechanism, based on the initial coordination of nitrile at cobalt is not confirmed. A novel gas buret system was used, which allowed automatic feed of ethyne under isobaric conditions and to monitor all reactants simultaneously on-line.     

The Synthesis and Dimerization of Transient 1-Silabutadienes

3-Methyl-1-tris(trimethylsilyl)silyl-2-butenol(1) ( 6 ) and (E)-3-Phenyl-1-tris(trimethylsilyl)silyl-2-propenol(1) ( 7 ) were prepared by the reaction of tris(trimethylsilyl)silyllithium ( 5 ) with 3,3-dimethylacrolein and (E)-cinnamaldehyde, resp. The alcohols 6 and 7 proved to be suitable precursors for the generation of the transient 1-silabutadienes (Me₃Si)₂Si = CHCH = CR¹R² 8 and 9 ( 8 : R¹ = R² = Me; 9 : R¹ = H, R² = Ph) following the principle of the modified Peterson reaction. Thus, 6 and 7 after deprotonation with excess MeLi in ether at low temperatures eliminated trimethylsilanolate and gave 8 and 9 , which were trapped by the excess organolithium reagent undergoing nucleophilic 1,2- or 1,4-addition reactions. In the absence of scavengers, e.g. when 8 and 9 were generated by treatment of 6 and 7 with stoichiometric quantities of MeLi in ether, the 1-silabutadienes dimerize in a [2 + 2] head-to-head fashion to give the 1,2-disilacyclobutanes 17 and 18 , resp., besides polymeric material. Treatment of the alcohol 6 with MeLi in tetrahydrofuran caused a 1,3-Si,O-trimethylsilyl shift affording the alkoxysilane (Me₃Si)₂SiH? CH(OSiMe₃)CH = CMe₂ 19 .