In 2- und 3-Stellung verzweigte,enantiomerenreine 4,4,4-Trifluor-3-hydroxy-buttersäure-Derivate aus 6-Trifluormethyl-1,3-dioxan-und -dioxin-4-onen

Preparation of Enantiomerically Pure 4,4,4-Trifluoro-3-hydroxy-butanoic Acid Derivatives, Branched in the 2- or 3-Position, from 6-Trifluoromethyl-1,3-dioxan- and -dioxin-4-ones Enantiomerically pure 3-hydroxy-3-trifluoromethyl-propionic acid and esters, substituted in the 2- or 3-position, are prepared (13 examples) from (R)- or (S)-4,4,4-trifluoro-3-hydroxy-butanoic acid. Key intermediates are the 2-t-butyl-6-trifluoromethyl-1,3-dioxan- and -dioxin-4-ones. The Li enolate of the cis-dioxanone is generated with t-BuLi and reacts with electrophiles (alkyl halides, aldehydes, imines, nitroolefins, Br₂, I₂) with predominant formation of trans,trans-2,5,6-trisubstituted dioxanones (9 examples). Elimination of HBr from the 5-Br-substituted dioxanone gives the (R)- or (S)-dioxinone, a chiral derivative of 4,4,4-trifluoro-3-oxo-butanoic acid (trifluoro-acetoacetate). Michael additions of cuprates or of CuCl-doped Grignard reagents to the dioxinone produce 6,6-disubstituted dioxanones (10 examples) bearing a CF₃ group in the 6-position. In most cases this addition is highly diastereoselective, with the new substituent winding up in the trans position. There are, however, surprising exceptions, such as the product formed with benzylmagnesium chloride which is an abnormal adduct with a p-quinoid structure ( 26 ) and with the newly introduced group in the cis position with respect to the t-Bu group. The structures of four trisubstituted dioxanones bearing CF₃ groups are determined by X-ray crystal structure analysis (Figure 1, Table 1), one of them including the absolute configuration (by anomalous diffraction). Besides the well-known sofa, a twist-boat conformation of dioxanones appears to be favorable. The solution conformations of the different types of CF₃-substituted dioxanones are derived from Nuclear Overhauser NMR measurements and compared with the crystal structures (Figure 3).     

New γ-pyrone propionates from the Indian Ocean sacoglossan Placobranchus ocellatus

A new γ-pyrone propionate, compound 9, and its peroxy derivative 10 have been isolated from the sacoglossan Placobranchus ocellatus. The structure and the relative stereochemistry of the new molecules, which displayed an unprecedented carbon skeleton characterised by a bicyclo [4.2.0] octane, have been determined by both spectroscopic methods and comparison with model compounds. By analogy with photodeoxytridachione (2), a sunscreen protective role could be also suggested for compound 9 in living P. ocellatus.     

A study of trialkyltin β-aryl-β-triphenylgermyl propionates

Twenty new compounds of the form Ph₃GeCHArCH₂COOSnR₃ (R = n-Bu, cyclohexyl; Ar = substituted phenyl) have been synthesized. Their structures were characterized by IR and ¹¹⁹Sn and ¹H NMR spectroscopy. The compounds are five-coordinated carboxylate bridged polymers when R = n– Bu; when R = cyclohexyl (Cy) they are four-coordinate. ¹¹⁹Sn NMR measurements of chemical shift for the two series of compounds have shown that there is a good linear relationship for the chemical shift of ¹¹⁹Sn NMR between the tributyltin and tricyclohexyltin propionates, viz. δ¹¹⁹Sn(Bu₃Sn) = 1.0474 δ ¹¹⁹Sn(Cy₃Sn) + 95.8076, n = 5, r = 0.993. The structure of one compound was determined by X-ray diffraction. It exists as a monomeric four-coordinated species in a distorted tetrahedronal geometry.     

COPPER(II) PROPIONATES Crystal and Molecular Structure of Bis(propionato)copper(II) Di(methyl-3-pyridylcarbamate)

Abstract

New copper(II) propionate compounds of composition Cu(prop)₂L (L =methyl-3-pyridylcarbamate or N, N-diethylnikotinamide) andau(prop)₂L₂ (L = methyl-3-pyr-idylcarbamate or2, 6-pyridinemethanole) have been prepared. The crystal and molecular structure of thetetrakis(μ-propionato)di(methyl-3-pyridinecarbamate) dicopper(II), Cu-₂(prop)₄(mpc)₂, was determined by direct method and Fouriertechniques. The compound crystallizes in the orthorhombic space group Pcab with four dimeric units in a cell withdimensions a = 19.350(4), b = 15.390(3), c = 10.725(2)Å. The structure was refined byfull-matrix least-squares methods to a R factor of 0.031, based on 3666 independent reflections. Thecompound is dimeric, with square-pyramidal geometry at each copper centre. The two copper atoms are bridgedby four carboxylate groups, while the apical ligands are methyl-3-pyridylcarbamate. The structural dataare compared with those found in similar copper(II) propionates. Spectral data of Cu(prop)₂L aretypical for dimeric copper(II) compounds. Both Cu(prop)₂L₂ compounds seem to possessoctahedral cop-per(II) stereochemistry with differing tetragonal distortion.     

Enantioselective N‐Heterocyclic Carbene Catalysis by the Umpolung of α,β‐Unsaturated Ketones

N‐Heterocyclic carbene‐catalyzed formation of β‐anionic intermediates from enones has been employed in the enantioselective synthesis of 2‐aryl propionates. The reaction was achievable using a homochiral 4‐MeOC₆H₄ morpholinone catalyst allowing the first example of enantioselective catalysis by umpolung of α,β‐unsaturated ketones. The reaction is high yielding, and shows robustness with reasonable generality. A mechanism is proposed in which the enantiodetermining protonation is achieved using either hexafluoroisopropanol or the formed naphthol product.     

三苯基锗杂环羧酸酯的合成与表征

合成了8种三苯基锗杂环羧酸酯Ph~3GeO~2CR(R=2-呋喃、2-呋喃乙烯基、2-噻吩基、2-吡啶基、3-吡啶基、4-吡啶基、3-吲哚甲基、3-吲哚丙基),利用元素分析、红外光谱、核磁共振氢谱和质谱表征了这些化合物的结构。体外实验表明,这些化合物对MCF-7和WiDr癌细胞具有较好的抑制活性。     

三苯基锗炔基膦酸酯的合成和表征

０IntroductionInrecentyears，thechemistryoforganogermaniumcompoundswasextensivelystudiedbecauseoftheirbiologicalactivity犤１，２犦．Organotinderivativesofoxyandthiophosphorusacidarewell－known犤３～５犦．Inourearlywork，theorganotinderivativesofalkynyloralkenylphosphateweresynthesizedandtheirstructuresandbiologicalactivitieswerealsostudied犤６～８犦．Sofar，tri－organogermaniumderivativesofphosphonicacidhavenotbeenreported．Inthispaper，O－bis（triphenylgermanium）alkynylphosphatesandO－trip…     

Crystallographic report: Crystal and molecular structure of Ph3GeO2CC4H3O

The germanium atom in the title compound is in a distorted tetrahedral geometry defined by an oxygen donor, derived from an effectively monodentate carboxylate ligand, and three ipso‐carbon atoms from the phenyl substituents. Copyright © 2005 John Wiley & Sons, Ltd.     

The Meinwald reaction of alkyl propionates. Synthesis of the C1-C9 fragment of aurisides

The C1-C9 northern fragment of aurisides 12a was prepared in eight steps and 41% overall yield starting from Grieco's bicyclic lactone (+)-4. The synthesis features a key stereoselective Meinwald reaction of the lithium enolate of alkyl propionate with the functionalized δ-lactone 3.