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The 1,3-dipolar cycloaddition reaction of (E,E)-1,3-bis(arylidene)indan-2-one with diarylnitrilimines, generated in situ via dehydrohalogenation of the corresponding hydrazonoyl chlorides , affords predominantly monospiropyrazolines and as a mixture of diastereoisomers. Also dispiropyrazolines are formed in moderate yields. The structure and stereochemistry of cycloadducts were confirmed by 1H and 13C-NMR spectroscopy, elemental analyses data, and single-crystal X-ray diffraction studies of and .

Synthesis of a series of cyclic fused-isoxazolines has been accomplished by regioselective and diastereoselective 1,3-dipolar cycloaddition of 3-methylindan-1-one enamines (1a, 1b, 1c) and 3-phenylindan-1-one enamines (2a, 2b, 2c) to arylnitrile oxides (3d, 3e, 3f, 3g, 3h). The structure of the cycloadducts was elucidated by 1H and 13C NMR spectroscopy. The proposed regio- and stereochemistry of fused-compounds (4) and (5) has also been corroborated by two single-crystal X-ray diffraction studies carried out on 4-methyl-8b-morpholinyl-3-(p-tolyl)-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (4be) and 3-(p-anisyl)-4-phenyl-8b-pyrrolidinyl-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (5af) and by means of density functional theory calculations.

Microwave-assisted 1,3-dipolar cycloaddition of (E,E)-1,3-bisarylidenetetral-2-ones with nitrilimines, generated in situ by dehydrohalogenation of the corresponding hydrazonoyl chlorides, affords a series of spiropyrazolines in good to excellent yields. The presence of a second exocyclic CC bond also allows the preparation of dispiropyrazolines. The cycloaddition proceeds with high chemo-, regio- and diastereoselectivity. The structure of the spiranic adducts has been established on the basis of their spectroscopic data and elemental analyses. The stereochemistry of these N-heterocycles has been confirmed by two X-ray diffraction studies. The luminescence properties and fluorescence quantum yields of these heterocyclic compounds have been investigated revealing that some of them are fluorescent in solution.

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused piperazines through a stepwise [3 + 3] cycloaddition pathway is observed. The stereochemistry of these N-heterocycles has been confirmed by several X-ray diffraction studies. Some of these compounds exhibit extensive hydrogen bonding in the crystalline state. To enlighten the observed regio- and stereoselectivity of the [3...

The synthesis and spectroscopic characterization of [Cp*2Mo2P2Se3] (1; Cp* = C5Me5) and its use as a molecular building block in the formation of copper(I) halide polymers is described. The reaction of 1 in CH2Cl2 with 2 equiv. of CuBr and CuI in CH3CN under diffusion conditions gave [(Cp*2Mo2P2Se3)2(CuBr)2] (2) and [(Cp*2Mo2P2Se3)(CuX)3(CH3CN)]n (X = I; 3/4), respectively. The structure of 2 is distinguished by a central Cu2Br2 ring coordinated on each side by a tripledecker complex through one of its P atoms. A 2D network is formed by weak interactions between Se atoms of neighboring molecules. Compound [(Cp*2Mo2P2Se3)(CuI)3(CH3CN)]n exists in two isomeric forms 3 and 4. The crystal structure of 3 can be described as a two-dimensional polymer that is formed by ribbons containing looped chains of three Cu2I2 rings and attached [Cp*2Mo2P2Se3] molecules. The structure of 4 contains a ribbon in which tripledecker molecules are linked through their P atoms to (CuI)6 clusters. The ribbons are connected by weak Se···Se interactions. The reaction of a mixture of 1 and P4Se3 with CuI gave [(Cp*2Mo2P2Se3)(P4Se3)(CuI)2]n. The crystal structure analysis of 5 reveals a new type of organometallic–inorganic framework in which 1 and P4Se3 are linked by Cu2I2 rings.

The oxidative addition of (2,2-dibromovinyl)ferrocene [Br2C=C(H)–Fc] (1) to [Pd(PPh3)4] yields the heterodinuclear σ-alkenyl complex trans-[{Pd(Br)(PPh3)2}–C(Br)=C(H)–Fc] (2). Nucleophilic attack of sodium thiolates on 1 unexpectedly affords the vinyl thioether derivatives (Z)-[(RS)(H)C=C(H)–Fc] (4a: R = Ph; 4b: R = tBu; 4c: R = Et). Complexes 4a and 4c can also be prepared by addition of NaSR across the triple bond of Fc–C≡C–H (3). Addition of an excess of NaSR to 1 affords the dithioether derivatives (Z)-[(RS)(H)C=C(SR)–Fc] (5a: R = Ph; 5b: R = p-tolyl; 5c: R = Et). An addition/elimination sequence is suggested to account for this surprising result. The yield of 5c is very low due to a competing formation of ethynylferrocene (3). Reaction of 5b with [Re(thf)(CO)3(μ-Br)]2 and [PtCl2(PhCN)2] leads to the heterodinuclear chelate complexes [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}Re(Br)(CO)3] (6) and [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}PtCl2] (7a), respectively. Metathesis of the fluxional compound 7a in the presence of NaI affords [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}PtI2] (7b). The electrochemical properties of some of these complexes have been studied by means of cyclic voltammetry, and the molecular structures of 1, 2, 3, 4b, 4c and 6 have been determined by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The reaction of [Ni(COD) 2 ] with [Cp* 2 NbTe 2 H] (1; Cp * = η-C 5 Me 5 ) in the presence of Ph 2 PCH 2 PPh 2 (dppm) in boiling toluene gives black-violet [(Cp * 2 Nb) 2 NiTe 4 ] (3). If [Cp' 2 NbTe 2 H] (2; Cp' = tBuC 5 H 4 ) is used under similar conditions dark-brown [(Cp'Nb)2Ni5Te7(dppm)2] (4) is formed. The structures of 3 and 4 have been determined crystallographically. Complex 3 contains a severely distorted NiTe 4 tetrahedron to which two niobocene groups are coordinated. Density functional analysis of the electronic structure of the NiTe 4 building block shows that it is best described as an [Ni(η 2 -Te 2 ) 2 ] 2- fragment. The structure of 4 reveals the presence of two Ni 5 and Te 5 tetragonal pyramids stacked into each other in an opposite way. Six of the Te bridges form two triangular faces, each of which is capped by a Cp'Nb fragment. Additionally, two dppm ligands bridge the long Ni-Ni edges of the Ni 4 bases. Oxidation of 3 with [(C 5 H 5 ) 2 Fe]BPh 4 gives paramagnetic [(Cp* 2 Nb) 2 NiTe 4 ]BPh 4 (6), whereas oxidation with [(C 5 H 5 ) 2 Fe]PF 6 proceeds with fluoride transfer to give [Cp* 2 NbF 2 ]PF 6 (5). Electrochemical studies of 3 reveal the existence of the redox couples [3]2+/[3]+/[3]°/[3] - /[3] 2- . Density functional calculations carried out on the different oxidation states of 3 reveal the following main features: the persistent presence of Nb-Ni bonds and the retention of Te-Te bonds in cationic and neutral species and their breaking off in reduced forms. Irrespective of the initial site of electrochemical attack, the Te atoms and Cp rings are principally affected in the final products.

Novel dispiropyrrolothiazole derivatives (IV) and (VI) are synthesized under mild reaction conditions in a complete regio- and stereoselective manner using three-component 1,3-dipolar cycloaddition reactions of cyclic diketones (I) or (V) with thiazolanecarboxylic acid (II) and arylidenepyrolidinedione (III) The dispiropyrrolothiazole derivatives (IVf) and (IVg) are found to exhibit significant antimycobacterial activity and emerge as the most promising antitubercular agents.

Congenital genu recurvatum (CGR) is a condition rarely observed during pregnancy. It is characterized by hyperextension of the knee, marked limitation of flexion, and a forward curvature of the lower extremities. It is also known as the back knee deformity. Prenatal diagnosis is possible with the use of sonography. Sonography allows imaging of the entire limbs, as well as assessment of position and mobility. When 3-dimensional (3D) and real-time 3D (4-dimensional) sonography are added to the scan, a more dynamic evaluation of the rendered limb(s) is possible; this further enhances the ability to detect abnormal positioning and movements of the limbs and to assess the relationship of the limbs to each other as well as to the rest of the fetal body. A review of the literature revealed only 1 other case in which prenatal diagnosis of isolated CGR was made. 1 We report a case of isolated postural CGR diagnosed at 21 weeks with both 2-dimensional (2D) and 3D sonography.

Treatment of 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl2C=C(H)-N=CPh2] (1) with excess sodium isopropylthiolate or sodium thiophenolate in DMF yielded the 2-azabutadiene derivatives (RS)2C=C(H)–N=CPh2 (2) (2a R = iPr; 2b R = Ph). Nucleophilic attack of the sodium salt of ethyl thioglycolate on 1 afforded as the sole product the six-membered heterocyclic compound ethyl 2-ethoxycarbonylmethylthio-5,5-diphenyl-5,6-dihydro-4H-1,4-thiazine-6-carboxylate (5). The reaction is initiated by substitution of the two vinyl-bound chloro substituents to give {EtO(O=)CCH2S}2C=C(H)–N=CPh2 (2c) as intermediate. A mechanism that accounts for the subsequent cyclisation reaction is proposed. The 2-azabutadiene derivative (PhO)2C=C(H)–N=CPh2 (7) was obtained by the reaction of 1 with sodium phenolate. The regioselectivity of the incoming nucleophile is roughly correlated with its hardness/softness in accord with Pearson’s HSAB principle. The molecular structures of 2a,b, 5 and 7 were determined by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Four deuterium-labelled ABA catabolites of high isotopic purity were prepared for hormone profiling studies using HPLC-ESI-MS-MS. The catabolites, namely [7′,7′,7′-d3]-PA, [7′,7′,7′-d3]-DPA, [5,8′,8′,8′-d4]-7′-hydroxyABA and [4,5,8′,8′,8′-d5]-ABA glucose ester were prepared either by biotransformation or chemical synthesis starting with labelled ABA. The labelled compounds are employed as internal standards for plant hormone profiling by liquid chromatography–electrospray–tandem mass spectrometry. Copyright © 2005 John Wiley & Sons, Ltd.

The preparation of a family of dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, i = 4 (1); Cp′ = η5-C5H4SiMe3, M = Nb, i = 3 (2); Cp′ = η5-C5H4SiMe3, M = Nb, i = 2 (3); Cp′ = η5-C5Me5, M = Nb, i = 4 (4); Cp′ = η5-C5Me5, M = Nb, i = 3 (5); Cp′ = η5-C5H4SiMe3, M = Ta, i = 4 (6); Cp′ = η5-C5H4SiMe3, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl3}2(μ-1,i-NC6H4N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C5H4(SiMe3)2 or C5Me5(SiMe3). Complexes 1−7 can also be prepared by the reaction of two equivalents of [MCp′Cl4] (Cp′ = η5-C5H4SiMe3, M = Nb, Ta; Cp′ = η5-C5Me5, M = Nb, Ta) with one equivalent of the corresponding aniline compound, N,N,N′,N′-tetrakis(trimethylsilyl)-1,4-, -1,3-, or -1,2-phenylenediamine, respectively. The synthesis of [{Ta(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5Me5, i = 4 (8); Cp′ = η5-C5Me5, i = 3 (9)] was only successful with the second preparative method. The reaction of 1, 2 and 8 with alkylating reagents gave the corresponding tetraalkyl derivatives, [{M(Cp′)R2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 4 (10); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 4 (11); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 4 (12); Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 3 (13); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 3 (14); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 3 (15); Cp′ = η5-C5Me5, M = Ta, R = Me, i = 4 (16); Cp′ = η5-C5Me5, M = Ta, R = CH2SiMe3, i = 4 (17); Cp′ = η5-C5Me5, M = Ta, R = CH2Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp′)(Me)(X)}2(μ-1,4-NC6H4N)] [Cp = η5-C5H4SiMe3, M = Nb, X = Cl (19); Cp = η5-C5H4SiMe3, M = Nb, X = NMe2 (20); Cp = η5-C5Me5, M = Ta, X = Cl (21)], were also prepared. The molecular structures of complexes 1, 8 and 17 were determined by single-crystal X-ray diffraction studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The complex [Cp*{C5H4(CH2CH2NMe2)}TaCl2] (1) was synthesised by reaction of the lithium salt LiC5H4(CH2CH2NMe2) with the tantalum compound [Cp*TaCl3(PMe3)]. Reduction of 1 with NaAl(H)2(OCH2CH2OMe)2 leads to the trihydride derivative [Cp*{C5H4(CH2CH2NMe2)}TaH3] (2). The oxidation of 2 in THF with ferrocenium ion leads to a cationic dihydride intermediate [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) with an intramolecular stabilization by the aminoethyl side-chain of the cyclopentadienyl ligand. The hemilabile character of the functionalised cyclopentadienyl ligand was checked by treating 3 with electron-donating ligands (e.g. phosphanes, sulfides, anions); in all cases, no displacement of the amino group was observed. When treated with HBF4, 2 undergoes a loss of the hydride and the resulting cation can be isolated as a solvento adduct by carrying out the reaction in dimethyl sulfide. Acidolysis of 2 in the presence of an excess of trifluoroacetic acid affords the compound [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). Microanalytical and NMR spectroscopic data for these complexes are given. The X-ray crystal structures are reported for [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) and [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

4,4-Dichloro-1,1-diphenyl-2-azabuta-1,3-diene (1) oxidatively adds to [Pd(PPh3)4] and [Pt(C2H4)(PPh3)2] giving rise to the σ-alkenyl complexes trans-[MCl{[C(Cl)=C(H)−N=CPh2]}(PPh3)2] (2a: M = Pd; 2b: M = Pt). When 1 is treated with [Pd(PPh3)4] in a 1:2 ratio in refluxing toluene, the dimetallic μ-vinylidene complex [(PPh3)ClPd{μ-[C=C(H)−N=CPh2]}PdCl(PPh3)2] (3) is formed. In this fluxional compound, a PPh3 ligands migrates in a reversible manner between the two Pd centers. Substitution of the PPh3 ligands of 3 by 2 equiv. of Ph2PCH2PPh2 affords the A-frame complex [ClPd(μ-dppm)2{μ-[C=C(H)−N=CPh2]}PdCl] (4). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A series of cyclic fused-isoxazolines is obtained by regioselective and diastereoselective 1,3-dipolar cycloaddition of enamines (I) and (IV) to arylnitrile oxides.

The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Huckel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: significant shortening of the Fe-Fe distance (deltad(Fe-Fe)> 0.3 A) and weakening of the As-As bond length ((deltad(As-As) > 0.3 A) suggests the formal presence of two diatomic AsSe ligands and a Fe-Fe bond. DFT and EHMO calculations confirm that an electron is removed from an occupied Fe-Fe orbital of antibonding character during oxidation. All molecular orbitals lower their energies upon oxidation, but the energy drop is relatively small for those involving the As-As bond. An additional structural feature in 4 consists of an electronic interaction of the iodide with both As atoms which suggests a formally neutral ion pair. Electrochemical studies confirm that the oxidation of 1 is a reversible one-electron process with E(1/2)= +0.07 V (in THF). These studies also reveal that 4 dissociates in polar solvents, such as THF, into [1]+ and I-, which is followed by transformation into 1 and I3.

Chloro-bridged bimetallic complexes (η5-C5H5)[η5-C5H4PPh2M′(CO)4]W(μ-Cl)X [X = Cl (3), × = H (4); M′ = Cr, W] were prepared by photochemical irradiation of (η5-C5H5)[η5-C5H4PPh2M′(CO)5]WClX [X = Cl (1), × = H (2); M′ = Cr, W]. The reactivity of the chloro-bridged complexes towards Lewis bases was studied; by exposure to CO or phosphanes, a facile cleavage of the chloro bridge accompanied by regio- and stereospecific coordination at M′ occurs. The X-ray structure of complex 3 (M′ = W) is reported.

Reaction of the title imines with diphenyldiazomethane gives a Δ3-1,3,4-triazoline, which leads, after loss of dinitrogen, to a transient azomethine ylide. Subsequent elimination of ethyl or methyl chloroformate gives the unexpected 1,1-diphenyl-4,4-dichloro-2-aza-1,3-butadiene.

The reactions of [Cp#2NbBH4] (1) [Cp# = C5Me5 (Cp*) or C5Me4Et] and [Cp′2TaH3] (Cp′ = tBuC5H4) with elemental selenium give complexes of the general composition [Cp2MSe2H]. These exist in three isomeric forms, A–C, depending on the metal and the chalcogen. [Cp#2NbSe2H] (2) incorporates the novel η2-Se2H ligand (C), which is labile when exposed to light. Solutions of 2(Cp*) can be converted into [Cp*2NbSe2H] (3), which exists in two isomeric forms A or B, along with [Cp*2NbSe3H] (4) and [Cp*2NbO2H] (5). [Cp′2Ta(η2-Se2)H] (6) is the only isomer found for the Ta system. Se abstraction by means of P(OEt)3 gives [Cp′2Ta(=Se)H] (7). Complex 7 can be reduced with Na/Hg and subsequently hydrolysed to give [Cp′2Ta(SeH)H2] (8), which has also been observed during the formation of 6. Coordination of [W(CO)5THF] at the Se lone pair of 7 affords the heterobimetallic complex 9. All compounds have been characterized by means of 1H- and, in some cases, 77Se-NMR spectroscopy. Products 8 and 9 have also been subjected to X-ray diffraction analysis.

Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by 1H, 77Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.

A four-step protocol for the synthesis of 2-fluoromethyl and 2-hydroxymethyl 4-alkyl furans 1a and 1b from a-alkyl acroleins 4 and 1-bromo-1-trimethylsilylethylene (5) via allene oxides 2 is elaborated, and is applied to the preparation of steroid furans 10, 11, 14 and 15 from α,β-unsaturated aldehyde 8.

Synthesis of (S)-methylenecyclopropaneacetic acid starting from L-(−)-malic acid, via (2S)-O-tert-butyldimethylsilyl-1,2-epoxybutan-4-ol and 1-O-tert-butyldiphenylsilyl-5-benzenesulfonyl-6-trimethylsilylhexane-1,3-diols as the key intermediates, is described.

Digitoxigenin ( I ) was obtained from 17-oxoandrost-5-en-3β-yl acetate ( III ) using, as a key step, free radical stereoselective substitution of an iodine atom in VI by a nitrile group. Transformation of the nitrile group at C-17 into a pregnane side chain or a butenolide lactone ring took place without isomerization at C-17.

The reaction of β-trimethylsilylalkyl sulfones ( 4a – 4b ) with oxirane derivatives ( 5a – 5d , 9 ) followed by treatment of the immediate adducts with sodium hydride, affords O-trimethylsilyl homoallylic alcohols ( 7a – 7e , 11 ), mainly (Z) isomers.

Optically active α-fluoroketones (96–97% ee) were obtained by the regioselective opening of chiral allene oxides with anhydrous tetrabutylammonium fluoride.

An efficient and highly stereoselective synthesis of the A-ring synthon 4 of 1,25(OH)2-vitamin D3 (1) is described. The aldehyde 12, which was used for an intramolecular ene reaction to form the main framework 18, was obtained by two different asymmetric approaches starting from olefin 6.

Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by 1H, 77Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.

Optically active γ-hydroxy-β-keto phosphonates 8 (96–97% ee) were obtained starting from 1-trimethylsilyl-1 -alkynes 1 by employing chiral allene oxides for introduction of α-hydroxy carbonyl functionality.

The reaction of the hydrofluoroborate salt of an open-chain analogue of a Reissert compound with some α,β-ethylenic esters does not give a [4 + 2] cycloadduct, as previously described in the case of ethyl acrylate. The reaction starts with a 1,3-dipolar cycloaddition of a munchnone imine 5c, d. The [3 + 2] cycloadducts 13 evolve via a rearrangement–condensation sequence to give a substituted 2-pyridone derivative 18 or 19. The proposed mechanism has been verified by the isolation and structural X-ray analysis of some compounds of the reaction sequence.

New dipeptides, structural analogues of known immunomodulating agents, were prepared by stereospecific condensation between 2-substituted thiazolidine-4-carboxylate esters with N-substituted L-proline or L-thiaproline. The structure of these compounds has been elucidated by combination of NMR methods and X-ray analysis. In addition, NMR measurements on dipeptides indicated the presence of S-cis and S-trans conformers around the amide bonds.

A series of new 2-substituted thiazolidine-4-carboxamide derivatives which have potentially useful immunological properties, have been synthesized in a stereoselective manner by coupling 2-subsituted thiazolidine-4-carboxylic acids with amines or amino esters. The structure of these compounds was established by combination of NMR methods and by X-ray analysis.

Recent studies clearly show the utility of the carbodiimide protocol to attach the redox-active Fc moiety to the N-terminal side of amino acids and peptides under mild conditions, resulting in stable and often crystalline products that afford themselves to structural analysis by X-ray crystallography. Electrochemical studies of Fc-peptides show that there is a significant influence of the redox potential depending on the amino acid sequence. The Fc moiety is sensitive to structural changes that occur in the peptide to which it is attached. For helical Fc-oligoprolines, the redox potential of the Fc group makes it easier to oxidize as the oligoproline chain increases in length. Nonhelical peptides, having a similar primary but different secondary structure, give rise to very different redox potentials. The ramifications of these findings to biological systems are significant in that they provide further evidence that the redox properties of a metal center are influenced by factors that go beyond the primary ligand sphere and thus for the involvement of long-range interactions. The Fc group is clearly sensitive to the shape of the peptide. These effects are currently under more detailed investigation [45] in order to gain further insight into the electronic structure of these ferrocenoyl peptides. Although we are not yet in a position to distinguish between "sensing" coordination or "sensing" conformation changes, this effect is of interest because it may allow the development of peptidic sensors.

The 1α-hydroxy A-ring phosphine oxide 1, a useful building block for vitamin D analogues, was synthesized from (S)-carvone in nine synthetic operations and a single chromatographic purification in 25% overall yield. The synthesis features two novel efficient synthetic transformations: the Criegee rearrangement of α-methoxy hydroperoxyacetate 10 in methanol to obtain directly the desired secondary 3β-alcohol 11 and the highly chemo- and stereoselective isomerization of dieneoxide ester (E)-7 to the 1α-allylic alcohol with an exocyclic double bond (E)-8. Further insight into the selectivity control of the latter rearrangement was obtained from the reactions of (Z)-epimeric substrates. The new synthetic approach leading to the 1α-hydroxy epimers complements our previously reported synthesis of the corresponding 1β-epimers, thus producing all stereoisomers of these versatile building blocks efficiently from carvone.