Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

Regio- and stereoselective reactions of a rhodanine derivative with optically active 2-methyl- and 2-phenyloxirane

The reaction of a rhodanine derivative (=(Z)-5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one; 1) with (S)-2-methyloxirane (2) in the presence of SiO₂ in dry CH₂Cl₂ for 10 days led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(2) (Scheme 2). The analogous reaction of 1 with (R)-2-phenyloxirane (5) afforded also two diastereoisomeric spirocyclic 1,3-oxathiolanes 6 and 7 bearing the Ph group at C(3) (Scheme 3). The structures of 3, 4, 6, and 7 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that oxiranes react selectively with the thiocarbonyl group (CS) in 1. Furthermore, the nucleophilic attack of the thiocarbonyl S-atom at the SiO₂-activated oxirane ring proceeds with high regio- and stereoselectivity via an S_N2-type mechanism.     

An efficient microwave assisted synthesis of novel class of Rhodanine derivatives as potential HIV-1 and JSP-1 inhibitors

(Z)-5-(2-(1H-Indol-3-yl)-2-oxoethylidene)-3-phenyl-2-thioxothiazolidin-4-one (7a-q) derivatives have been synthesized by the condensation reaction of 3-phenyl-2-thioxothiazolidin-4-ones (3a-h) with suitably substituted 2-(1H-indol-3-yl)-2-oxoacetaldehyde (6a-d) under microwave condition. The thioxothiazolidine-4-ones were prepared from the corresponding aromatic amines (1a-e) and di-(carboxymethyl)-trithiocarbonyl (2). The aldehydes (6a-h) were synthesized from the corresponding acid chlorides (5a-d) using HSnBu₃.     

On the microstructure and symmetry of apparently hexagonal BaAl2O4

The P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P6₃ (a=2a_p, b=2b_p, c=c_p) structure model for BaAl₂O₄ to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6₃22 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (∼10 nm in diameter) are used to show that the P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic.     

New A-ring analogs of the hormone 1α,25-dihydroxyvitamin D3: (2′-hydroxymethyl)tetrahydrofuro[1,2-a]-25-hydroxyvitamin D3

Conceptually new, enantiomerically pure bicyclic tetrahydrofuro[1,2-a]-A-ring phosphine oxides (+)-4 and (−)-4 were successfully prepared from methyl 2-pyrone-3-carboxylate and (S)- or (R)-2-(tert-butyldimethylsilyloxy)methyl-2,3-dihydrofuran, respectively. In addition, (2′-hydroxymethyl)tetrahydrofuro[1,2-a]-25-hydroxyvitamin D₃3a and 3b as new A-ring-modified analogs of the natural hormone 1α,25-dihydroxyvitamin D₃ were readily synthesized by using Lythgoe-type coupling of the A-ring phosphine oxides (+)-4 and (−)-4 with C,D-ring ketone (+)-5.     

A highly stereoselective preparation of CF3-substituted 1-aryl-1,2-diphenylethenes: application to the synthesis of panomifene

β-CF₃-α,β-diphenylvinyl sulfide 3a was prepared stereoselectively in 77% yield from the reaction of 2 with phenyllithium at room temperature for 5 h. Oxidation of 3a with MCPBA afforded the corresponding vinyl sulfone 4a, in which (E)-4a can be crystallized in a mixture of CH₂Cl₂ and hexane. The addition-elimination reaction of (E)-4a with phenyllithium having substituents on the benzene ring provided 5a-j in 51-82% yields stereospecifically. Similarly, the treatment of (E)-4a with p-chloroethoxyphenyllithium in the presence of 12-crown-4 (20 mol %) at −10 °C, followed by slowly warming to room temperature, resulted in the formation of the corresponding panomifene precursor 6 in 82% yield.     

Synthesis,structural analysis,and thermal and spectroscopic studies of methylmalonate-containing zinc(II) complexes

The synthesis, crystal structure, thermal analysis and spectroscopic studies of five zinc(II) complexes of formulae [Zn(Memal)(H₂O)]_n (1) and [Zn₂(L)(Memal)₂(H₂O)₂]_n (2-5) [H₂Memal = methylmalonic acid, and L = 4,4′-bipyridine (4,4′-bpy) (2), 1,2-bis(4-pyridyl)ethylene (bpe) (3), 1,2-bis(4-pyridyl)ethane (bpa) (4) and 4,4′-azobispyridine (azpy) (5)] are presented here. The crystal structure of 1 is a three-dimensional arrangement of zinc(II) cations interconnected by methylmalonate groups adopting the μ₃-κ²O:κO’:κO”:κO”’ coordination mode to afford a rare (10,3)-d utp-network. The structures of the compounds 2-5 are also three-dimensional and they consist of corrugated square layers of methylmalonate-bridged zinc(II) ions which are pillared by bis-monodentate 4,4′-bpy (2), bpe (3), bpa (4) and azpy (5) ligands. The Memal ligand in 2-5 adopts the μ₃-κO:κO′:κO′′:κO′′′ coordination mode. Each zinc(II) ion in 1-5 is six-coordinated with five (1)/four (2-5) methylmalonate-oxygen atoms, a water molecule (1-5) and a nitrogen atom from a L ligand (2-5) building distorted octahedral environments. The rod-like L co-ligands in 2-5 appear as useful tools to control the interlayer metal-metal separation, which covers the range 8.4311(5) Å (2) – 9.644(3) Å (5). The influence of the co-ligand on the fluorescence properties of this series of compounds has been analyzed and discussed by steady-state and time resolved spectroscopy on all five compounds in the solid state.     

Reversible pyranyl complex formation and the mechanism of rearrangement to (η-6-oxocycloheptadienyl)Mn(CO)3 complexes in the reaction of β-cyclomanganated 1,5-diarylpenta-1,4-dien-3-ones and alkynes; the crystal structure of [2,4-diphenyl-6-(2-phenylethenyl)pyranyl-η]tricarbonylmanganese

[1-Phenyl-2-[(E)-3-phenylprop-2-en-1-oyl-κO]ethenyl-κC¹]tetracarbonylmanganese (1a) reacts with PhCCH in CCl₄ at room temperature to form [2,4-diphenyl-6-(2-phenylethenyl)pyranyl-η⁵]tricarbonylmanganese (2a), whose X-ray crystal structure is reported to complement that of its isomer [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese (3a), previously obtained from the reaction under reflux; but for 1a and PhCCPh the pyranyl complex cannot be isolated before rearrangement to the 3a analogue occurs. More forcing reaction conditions for 1a with Me₃SiCCH and for [1-(2-trifluoromethylphenyl)-2-[(E)-3-(2-trifluoromethylphenyl)prop-2-en-1-oyl-κO]ethenyl-κC¹]tetracarbonylmanganese (1b) with Me₃SiCCH and PhCCH give new analogues of 3a where previously only 2a analogues had been isolated.The reaction in CCl₄ under reflux of PhCCH and the β-deuterio analogue of 1a, [1-phenyl-2-[(E)-3-phenylprop-2-en-1-oyl-3d-κO]ethenyl-κC¹]tetracarbonylmanganese, gave deuteriated 3a with exo-D at the α-carbon, C7. This is inconsistent with the Mn-mediated Ph migration mechanism originally proposed to accommodate the endo position of Ph in 3a, and instead it implicates a cyclopropyl carbonyl-addition intermediate or a cyclopropyl acyl-substitution transition state in the key rearrangement step for 2a → 3a.     

Total synthesis of apigenin 7,4′-di-O-β-glucopyranoside, a component of blue flower pigment of Salvia patens, and seven chiral analogues

We have succeeded in the first total synthesis of apigenin 7,4′-di-O-β-d-glucopyranoside (1a), a component of blue pigment, protodelphin, from naringenin (2). Glycosylation of 2 according to Koenigs-Knorr reaction provided a monoglucoside 4a in 80% yield, and this was followed by DDQ oxidation to give apigenin 7-O-glucoside (12a). Further glycosylation of 4′-OH of 12a with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl fluoride (5a) was achieved using a Lewis acid-and-base promotion system (BF₃·Et₂O, 2,6-di-tert-butyl-4-methylpyridine, and 1,1,3,3-tetramethylguanidine) in 70% yield, and subsequent deprotection produced 1a. Synthesis of three other chiral isomers of 1a, with replacement of d-glucose at 7 and/or 4′-OH by l-glucose (1b-d), and four chiral isomers of apigenin 7-O-β-glucosides (6a,b) and 4′-O-β-glucosides (7a,b) also proved possible.     

3-Oxyanthranilic acid derivatives from Actinomadura sp. BCC27169

Eight new compounds including 9′-[2-amino-3-(4″-O-methyl-α-rhamnopyranosyloxy) phenyl]nonanoic acid (1), 9′-[2-amino-3-(4″-O-methyl-α-ribopyranosyloxy)phenyl] nonanoic acid (2), 11′-[2-amino-3-(4″-O-methyl-α-rhamnopyranosyloxy)phenyl]undecanoic acid (3), 11′-[2-amino-3-(4″-O-methyl-α-ribopyranosyloxy)phenyl]undecanoic acid (4), 8-(4′-O-methyl-α-rhamnopyranosyloxy)-3,4-dihydroquinolin-2(1H)-one (5), 8-(4′-O-methyl-α-ribopyranosyloxy)-3,4-dihydroquinolin-2(1H)-one (6), 8-(4′-O-methyl-α-rhamnopyranosyloxy)-2-methyquinoline (7), and 8-(4′-O-methyl-α-ribopyranosyloxy)-2-methylquinoline (8) were isolated from Actinomadura sp. BCC27169. The chemical structures of these compounds were determined based on NMR and high-resolution mass spectroscopy. The absolute configurations of these monosaccharides were revealed by the hydrolysis of compounds 7 and 8. Compounds 3 and 8 exhibited antitubercular activity at MIC 50 μg/mL. Only compound 3 showed cytotoxicity against KB cell at IC₅₀ 18.63 μg/mL, while other isolated compounds were inactive at tested maximum concentration (50 μg/mL).     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Assembly of diverse structural types of organotellurium compounds in the reactions of (4-MeO-C6H4)2TeO with pyridine carboxylic acids

The reactions of Ar₂TeO (Ar = 4-MeO-C₆H₄) with 2-, 3- and 4-pyridine carboxylic acids (LH) afforded different organotelluroxane structural types depending on the stoichiometry of the reactants and the conditions of the reaction. Ar₂Te(L)OH (1a-1c) are formed in a 1:1 reaction of Ar₂TeO with LH in the presence of water. On the other hand a 1:2 reaction under anhydrous conditions leads to the formation of Ar₂TeL₂ (2a-2c). A 2:2 reaction under anhydrous conditions affords the ditelluroxanes Ar₂Te(L)OTe(L)Ar₂ (3a-3c) while tritelluroxanes Ar₂Te(L)OTeAr₂OTe(L)Ar₂ (4a-4c) are formed in 3:2 reactions. Interestingly, 3a-3c are formed in the reaction of 2a-2c with Ar₂TeO. The former can be hydrolyzed to 1a-1c while the latter upon reaction with Ar₂TeO lead to the formation of the tritelluroxanes 4a-4c. Attempts to metalate 2a with PdCl₂(MeCN)₂ leads to a transfer of the carboxylate ligand to palladium affording Ar₂TeCl₂ and PdL₂. X-ray crystal structures of representative examples of the family of 1, 2 and 3 reveal interesting supramolecular structures and the formation of a novel [TeO]₂ structural unit. The latter results from intermolecular secondary Te?O interactions.     

Polyhydroxylated pyrrolidines: synthesis from d-fructose of new tri-orthogonally protected 2,5-dideoxy-2,5-iminohexitols

The readily available 3-O-benzyl-1,2-O-isopropylidene-β-d-fructopyranose (2) was transformed into its 5-O- (3) and 4-O-benzoyl (4) derivative. Compound 4 was straightforwardly transformed into 5-azido-4-O-benzoyl-3-O-benzyl-5-deoxy-1,2-O-isopropylidene-β-d-fructopyranose (7) via the corresponding 5-deoxy-5-iodo-α-l-sorbopyranose derivative 6. Cleavage of the acetonide in 7 to give 8, followed by regioselective 1-O-silylation to 9 and subsequent catalytic hydrogenation gave a mixture of (2S,3R,4R,5R)- (10) and (2R,3R,4R,5R)-4-benzoyloxy-3-benzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (12) that was resolved after chemoselective N-protection as their Cbz derivatives 11 and 1a, respectively. Stereochemistry of 11 and 1a could be determined after total deprotection of 11 to the well known DGDP (13). Compound 2 was similarly transformed into the tri-orthogonally protected DGDP derivative 18.     

Two novel Cu4O4 cubanes with functionalized chelating aziridine ligands

The synthesis and molecular structure of [Tetrakis{μ₃-(2-aziridin-1-yl-ethanolato-κ²N,O)-bromidocopper(II)] (5) and [Tetrakis{(N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine-κ²N,N′)-(μ₃-hydroxido)-copper(II)}]tetrabromide (7) is reported. Both chelate complexes are prepared from the corresponding bidentate aziridine ligands 2-(1-aziridinyl)ethanol (3) and N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine (4), respectively and CuBr₂ (1) or CuBr (2, by redox reaction), in dry dichloromethane. Both compounds crystallize in a distorted Cu₄O₄-cubane structure. In the neutral complex 5, the cube is formed by four μ₃-bridging oxygen atoms of the bidentate 2-aziridin-1-yl-ethanolato ligand formed by deprotonation of 3 and four square-pyramidal Cu(II) centers. In the cationic complex 7, the Cu₄O₄ core consists of four μ₃-hydroxido bridges situated at alternate vertexes to four also 5-coordinate Cu(II) centers. Both compounds are fully characterized by IR-spectroscopy, elemental analysis and X-ray structure analysis and describe the first examples of cubanes with aziridine ligands.     

Solvent-dependent formation of two different Cd(II) complexes with p-BrC6H4C(S)NHP(O)(OiPr)2 (HL). Crystallographic modification of Cd(HL)2L2

Reaction of the potassium salt of N-(diisopropoxyphosphoryl)-p-bromothiobenzamide p-BrC₆H₄C(S)NHP(O)(OiPr)₂ (HL) with Cd(II) cations in freshly dried and distilled EtOH leads exclusively to the complex [Cd(p-BrC₆H₄C(S)NH₂-S)(L-O,S)₂] ([Cd(L^I)L₂]), while the same reaction in H₂O leads to the complex [Cd(HL-O)₂(L-O,S)₂] ([Cd(HL)₂L₂]). The corresponding reactions with Zn(II) always lead to the complex [Zn(L-O,S)₂] ([ZnL₂]) regardless of the solvent. The crystal structure of [Cd(HL)₂L₂]^.2/3H₂O reveals to be a polymorph to the previously reported anhydrous [Cd(HL)₂L₂].     

Design and synthesis of boron containing 2,4-disubstituted-phthalazin-1(2H)-one and 3,7-disubstituted-2H-benzo[b][1,4] oxazine derivatives as potential HGF-mimetic agents

We synthesized boron containing 2-(4-methoxybenzyl)-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioaborolan-2-yl)phenyl) phthalazin-1(2H)-one 3 and 7-methyl-3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-2H-benzo[b][1,4] oxazine 8. The reaction of compound 2 with B₂pin₂ using potassium acetate as the base and Pd(PPh₃)₂Cl₂ as the catalyst, produced the corresponding boron-containing derivative 3 as a white solid in 65% yield. Alternatively, we have synthesized compound 8 as a yellow solid in 59% yield using the Miyaura borylation reaction. The potassium trifluoro(4-(-methyl-2H-benzo[b][1,4]oxazine-3-yl)phenylborate 9 was then obtained after treatment of 8 with aqueous solution of KF₂H in methanol as white solid product in 60% yield. The biological activities of the synthetic compounds are currently being evaluated.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

Syntheses and structural characterization of some mono- and di-p-nitrophenyl[3]ferrocenophanes: X-ray structure of [3]ferrocenophane, 3-p-nitrophenyl[3]ferrocenophane, and 3,4′-bis-(p-nitrophenyl)[3]ferrocenophane; DFT calculations on ferrocene derivatives

[3]Ferrocenophane (3a) reacts in a Gomberg reaction with diazotized p-nitroaniline to give a mixture of mono- and di-substituted products. The isomeric pairs of 3- and 2-(p-nitrophenyl)[3]ferrocenophanes (4 and 5), as well as 3,4′- and 3,4-bis-(p-nitrophenyl)[3]ferrocenophanes (6 and 7) were separated from the mixture by column chromatography on Al₂O₃ and characterized by means of mass, IR, UV, ¹H-NMR spectroscopy, and by X-ray analysis (4 and 6). PM3/tm and density functional theoretical calculations on ferrocene (1) and ferrocenophane derivatives are reported. A refined X-ray structure determination of [3]ferrocenophane (3a) is given.     

Synthesis and structural studies of some titanium and zirconium complexes with chiral bis(amide), amidinate or bis(amidinate) ligands

Reaction of bis(amide) sodium Na₂[(1R,2R)-(−)-1,2-(NSiMe₃)₂-C₆H₁₀] (Na₂[L¹]) with Ti(OiPr)₂Cl₂ in different conditions gave mixed-ligand complexes [Ti(OiPr)Cl][L¹] (1) or [Ti(OiPr)₂Cl]₂[L¹] (2); 2 is a dinuclear titanium example in which Ti atoms are bridged by nitrogen and oxygen atoms simultaneously forming a distorted rhombic core. Reaction of the amine-amidinate ligand (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-(NHSiMe₃)-C₆H₁₀(Li[L²]) or rarely linked bis(amidinate) ligand Li₂[(1R,2R)-(−)-1,2-{NC(Ph)N(SiMe₃)}₂-C₆H₁₀](Li₂[L³]) with ZrCl₄ yielded the unbridged and bridged bis(amidinate) complexes ZrCl₂[L²]₂ (3) and [ZrCl₂(THF)][L³] (4), respectively; Moreover, the reaction of (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-Li(NSiMe₃)C₆H₁₀(Li₂[L²]) with Ti(OiPr)₂Cl₂ gave a new type of tridentate amido-amidinate product [Ti(OiPr)₂][L²] (6), which is a distinct model compared to [Ti(OiPr)₂Cl][L²] (5) yielded from Li[L²]. All the products have been characterized by X-ray crystallography and the structural studies are presented detailedly comparing with relevant compounds.     

Interesting transformations of naturally occurring cassane diterpenoids and bioevaluation of the products

Two cassane diterpenoids, pulcharrin G (1) and 6β-cinnamoyl-7β-hydroxy-voucapen-5-α-ol (2), the constituents of Caesalpinia pulcherrima, were treated with BF₃·OEt₂ to furnish two olefinic products 3 and 4, respectively. The products were formed by elimination of water and migration of a methyl group from C-4 to C-5. The cytotoxic and antimicrobial activities of 3 and 4 were examined.