Anthracene coupled trans-pyridylcinnamide: a new fluororeceptor for selective sensing of dicarboxylates

trans-Pyridylcinnamide has been established as an alternative hydrogen bonding synthon, in place of urea for carboxylate binding. This alternative motif has been used in the design and synthesis of new fluorescent ‘On-Off’ signalling chemical sensor 1, which is found to bind aliphatic dicarboxylates with moderate binding constants. The recognition ability has been established by fluorescence, UV-vis and ¹H NMR spectroscopic methods. The receptor is found to be selective for long chain pimelate.     

Synthesis of novel chiral spirodione, (6R,7R)-7-phenyl-1-oxaspiro[5.5]undec-3-ene-2,5-dione: application to the asymmetric Diels-Alder reaction with high π-facial selectivity

The synthesis of the title spirodione, a new class of auxiliary based chiral synthon using (−)-trans-2-phenylcyclohexanol and its application to the asymmetric Diels-Alder reaction are described. Methodology for detachment of the chiral auxiliary from the cycloadduct has been developed.     

Furo[3,2-b]pyridine: a convenient unit for the synthesis of polyheterocycles

An efficient and rapid synthesis of furo[3,2-b]pyridine 1 is described using a one-pot Sonogashira coupling/heteroannulation sequence. Regioselective lithiation of this synthon was performed leading to various 2-substituted furo[3,2-b]pyridines. Some of them were used as substrates for short functional synthesis of polyheterocycles.     

Pt(II) stereoisomeric complexes with serine

There have been synthesized Pt(II) stereoisomeric complexes with hydroxy-α-amino acid serine (SerH = NH₂CH(CH₂OH)COOH is α-amino-β-hydroxypropionic acid): trans-[Pt(S-SerH)₂Cl₂], trans-[Pt(R-SerH)(S-SerH)Cl₂] with monodentately (through NH₂ group ) bound SerH and cis-, trans-[Pt(R-Ser)(S-Ser)], trans-[Pt(S-Ser)₂] with bidentately bound (through groups NH₂ and COO) ligands (R, S is the absolute configuration of asymmetric carbon atom). The successive phases in the synthesis of Pt(II) stereoisomeric complexes with serine were studied by ¹⁹⁵Pt NMR spectroscopy. To identificate the compounds synthesized the method of elemental analysis, IR and NMR (¹⁹⁵Pt, ¹³C, ¹H) spectroscopy were used. For trans-[Pt(R-Ser)(S-Ser)] the X-ray diffraction data were obtained.     

A Convenient Synthesis of the Important Retinoid Synthon Ethyl trans-3-formyl-2-butenoate

The efficient, high-yield synthesis of the important retinoic acid synthon ethyl trans-3-formyl-2-butenoate by Wadsworth-Emmons methodology is described.     

First total syntheses of (±)-3-aza-11-selena and (±)-3-aza-11-tellura steroids

An efficient synthesis of 11-selena and 11-tellura steroids bearing a pyridine as an A ring was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes, which were generated from a 3-azabicyclo[4.2.0]octa-1,3,5-trien-7-one ketal. The major isomer matches the trans-anti-trans ring configuration of natural products. Finally, the vinyl groups of the synthesized 11-hetero steroids have been oxidized by the Wacker process in good yields. The characteristic ¹H and ¹³C NMR spectroscopic features of the synthesized compounds are reported.     

NMR-Spectroscopic, computational and mass-spectrometric investigations on the cis/trans analogues of 2,3,4-trihydronaphthalene-1-one

NMR-Spectroscopic, computational and mass-spectrometric studies of the cis/trans isomers of N-[8-(acetylamino)-4-(2,2-dimethyl-1,1-diphenyl-silapropoxy)-6-fluoro-5-methyl-1-one-2,3,4-trihydronaphthyl]acetamide (1a and 1b), obtained as intermediates in the synthesis of an important class of alkaloid molecules, are reported. ¹H and ¹³C NMR analyses show an unusual axial preference of the TBDPSi- (tert-butyldiphenylsilyl) group in position 4 in both the isomers. Mass spectrometric evidence demonstrates that trans isomer has a higher affinity for ammonium ions than the cis isomer and that only the ammonium adduct [1b+NH₄]⁺ and the protonated molecule [1b+H]⁺ show the fragmentation in which loss of benzene is observed. Moreover, molecular mechanics and semi-empirical calculations indicate that a group of trans conformers tend to place one of the phenyl rings of the TBDPSiO- group in a offset π-stacked geometry with the compound's aromatic ring. The combination and the detailed analyses of these experimental and theoretical results could support the π-π interaction obtained as a conformational preference in the trans isomer.     

Development of the first and practical method for enantioselective synthesis of B-enriched p-borono-l-phenylalanine

At present p-(¹⁰B)borono-l-phenylalanine (l-¹⁰Bpa) is used clinically as an excellent ¹⁰B carrier for BNCT; however, its enantioselective synthesis has not been reported yet. The present Letter describes the first and practical method for enantioselective synthesis of ¹⁰B-enriched l-Bpa using Z-l-Ser-OMe as the chiral synthon in good total yield and high optical purity.     

Nickel(II), palladium(II) and platinum(II) complexes of trans spanning ditertiary phosphine 3,3′-oxybis- [(di-meta-tolylphosphino)methyl]benzene

The synthesis of the trans-spanning bidentate diphosphine ligand, 3,3′-oxybis-(di-meta-tolylphosphino)methyl]benzene (I) and its complexes with Ni^II, Pd^II and Pt^II are described. The ligand I forms monomeric trans square planar complexes [MX₂(I)] (M = Ni, Pd or Pt, X = Cl or X = NCS in case of Ni). ³¹P and ¹H NMR parameters are reported.     

An asymmetric synthesis of cis,anti, cis-tricyclo[5,3,0,02,6]decanes applying γ-hydroxymethyl-γ-butyrolactone as a chiral synthon. First asymmetric total synthesis of (−)-β-bourbonene

The asymmetric total synthesis of cis, anti, cis-tricyclo[5,3,0,0^2,6]decane sesquiterpene β-bourbonene is described. The key (2+2) photocycloaddition was carried out applying the optically pure butenolide derivative $\text{6b}$ as a chiral synthon.     

Further applications of endocyclic enamine-enone annulations : The total syntheses of rac-Sceletium alkaloid A4 and 3'-demethoxy sceletium alkaloid A4

The total synthesis of rac-sceletium alkaloid A₄1a and of its 3'-demethoxy analogue 1b via the annulation of endocyclic enamines 4a–b is presented. The Michael acceptor 5a is a useful synthon for the two-step synthesis of 2,3-disubstituted pyridines from Δ²-pyrrolines.     

An efficient synthesis of 7-hydroxy-2,6-dimethylchromeno[3,4-d]oxazol-4-one—a protected fragment of novenamine

The high-yielding six-step synthesis of 7-hydroxy-2,6-dimethylchromeno[3,4-d]oxazol-4-one 17 from commercially available 2,4-dihydroxy-3-methylacetophenone is described. Coumarin 17 constitutes a useful synthon for coumarin antibiotic synthesis. A new methodology for oxazole formation applicable to 3-aminocoumarins has been developed, and a mechanistic rationalization is proposed.     

2-cyano Δ3 piperidines vi1 : a general method for the stereoselective synthesis of cis and trans 2,6-dialkylpiperidine alkaloids

The cis 2,6-dialkylpiperidine alkaloid (±) dihydro-pinidine $\text{7b}$ and the trans alkaloid (±) solenopsin A $\text{5a}$ were synthesized from a common α-aminonitrile synthon $\text{1}$. The key step in this synthesis was the stereoselective reductive decyanation of the 1-benzyl-2cyano-2′, 6-dialkylpiperidines $\text{3a}$ and $\text{3b}$.     

The first highly stereoselective approach to the mitotic kinesin Eg5 inhibitor HR22C16 and its analogues

A general method for the synthesis of the mitotic kinesin Eg5 inhibitor HR22C16 1 and its analogues based on protecting group (PG)-modulated highly diastereoselective Pictet–Spengler reaction of l-tryptophan methyl ester hydrochloride with meta-(RO)-benzaldehyde is described. By using the enantiomerically pure (1R,3S)-1,3-disubstituted tetrahydro-β-carboline trans-4c as a common chiral synthon, HR22C16 1 and its analogues 2 and 3 were synthesized in 90.1%, 90.2%, and 86.5% overall yields, respectively.     

Metals in organic syntheses: XIV. NMR,IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes

Among the several hydrides formed when trans-[PtHClL₂] (L = PPh₃) reacts with Sncl₂, only trans-[PtH(SnCl₃)L₂] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl₃)L₂]. At −10°C, cis-[PtEt(SnCl₃)L₂] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable.At −50°C, a mixture of trans-[PtHClL₂] and trans[PtH(SnCl₃)L₂] reacts with ethylene to give cis-[PtEtClL₂] and cis-[PtEt(SnCl3)L₂] and this has been attributed to the catalytic activity of SnCl₂ which dissociates from cis-[PtEt(SnCl₃)L₂] at this temperature.Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl₃)L₂], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L₂]⁺ SnCl₃⁻. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L₂], trans-[Pt(SnCl₃)(COEt)L₂], trans-[PtCl(COEt)l₂ · SnCl₂], and trans-[Pt(COEt)(CO)L₂]⁺ SnCl₃⁻. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL₂] with SnCl₂.Trans-[PtH(SnCl₃)L₂] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl₃)(CO)₂L₂], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl₃)L₂] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl₃)L₂] is allowed to react with CO.The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.     

Synthesis and variable coordination modes of a bis-thiophene-appended macrocycle in complex with cobalt(III)

The bis-thiophene appended cyclam derivative L³ (trans-6,13-dimethyl-6,13-bis(thiophene-3′-ylmethylamino)-1,4,8,11-tetraazacyclotetradecane) has been synthesised, characterised and complexed with Co^III. The crystal structure of the diprotonated ligand as its cyanoborohydride salt [H₂L³][NCBH₃]₂ is reported. Variable coordination modes to Co^III have been identified that find the ligand binding either as a tetradentate (cyclam-like) macrocycle in the structurally characterised complexes trans-[CoL³Cl₂]Cl and trans-[CoL³(NCBH₃)(OH)]Cl or as a hexadentate in [CoL³]Cl₃ where both functionalised exocyclic amines coordinate in trans coordination sites. In this case, we have found that the structure of the hexadentate coordinated complex [CoL³]³⁺ is significantly tetragonally elongated due to steric effects of the thiophene rings and this also leads to a very large 500 mV anodic shift in the Co^III/II redox potential relative to the unsubstituted hexaamine complex of Co^III.     

The use of a thermostable signature amidase in the resolution of the bicyclic synthon (rac)-γ-lactam

The resolution of the bicyclic synthon (rac)-γ-lactam (2-azabicyclo[2.2.1]hept-5-en-3-one) is an important step in the synthesis of a group of chemotherapuetic agents known as carbocyclic nucleosides. The archaeon Sulfolobus solfataricus MT4 produces a thermostable γ-lactamase that has a high sequence homology to the signature amidase family of enzymes. It shows similar inhibition patterns of amidases towards benzonitrile, phenylmethylsulfonyl fluoride and heavy metals such as Hg²⁺, and is activated by thiol reagents. The enzyme selectively cleaves the (+)-enantiomer from a racemic mix of γ-lactam. It also exhibits general amidase activity by cleaving linear and branched aliphatic and aromatic amides. The enzyme catalyses the synthesis of benzoic hydrazide from benzamide preferentially to benzamide cleavage in the presence of excess hydrazine. This enzyme has potential for use in industrial biotransformations in the production of both carbocyclic nucleosides and hydrazides.     

A new method for the synthesis of metal complexes with <Emphasis Type="Italic">trans</Emphasis>-[B<Subscript>20</Subscript>H<Subscript>18</Subscript>]<Superscript>2–</Superscript> dianion

A new method has been proposed for the synthesis of transition metal complexes with the trans-[B₂₀H₁₈]^2– dianion from complexes with the closo-decaborate anion [B₁₀H₁₀]^2– without changing the cationic part of the complex. A cerium(IV) salt has been used as an oxidizing agent. Complexes [NiL₃][trans-B₂₀H₁₈] (L = Bipy, Phen) have been identified by elemental analysis and IR spectroscopy.     

Synthesis and characterisation of some salts of the ions [Rh(Oxalato)2(Rpy)2]−

Salts of three bisoxalato bis(pyridine) species, trans-[Rh(ox)₂(py)₂]^?, trans-[Rh(ox)₂(3-Mepy)₂]^? and trans-[Rh(ox)₂(4-Mepy)₂]^? have been isolated from the substitution of N-heterocycles into trisoxalatorhodate(III) and characterised on the basis of ¹H NMR and ¹³C NMR spectra, which are similar to that of the trans-[Co(oxalato)₂ (R-py)₂]^? complex.