Grety Rihs

4′,6′-Methano carbocyclic thymidine: A conformationally constrained building block for oligonucleotides

The synthesis of the title compound 1 has been accomplished in 20 chemical steps starting from D-ribonolactone. X-ray crystallography shows the bicyclic skeleton of 1 to adopt a boat-like (“2′-exo”) conformation and preliminary hybridization data indicate that the substitution of 1 for natural thymidine in DNA/RNA heteroduplexes may increase their thermodynamic stability.

1′,6′-methano carbocyclic thymidine: Synthesis, x-ray crystal structure, and effect on nucleic acid duplex stability

The title compound 1 has been synthesized via bicyclic lactone 3 and amine 9 as the key intermediates. X-ray crystallography reveals the bicyclic skeleton of 1 to adopt a boat-like (3′-exo) conformation. Oligodeoxyribonucleotides incorporating up to 10 building blocks 1 in place of natural thymidine are still capable of binding to complementary DNA or RNA, albeit with lower affinity than the unmodified parent compounds.

Chemo-enzymatic synthesis of 1,2- and 1,3- amino-alcohols and their use in the enantioselective reduction of acetophenone and anti-acetophenone oxime methyl ether with borane.

Abstract New chiral amino-alcohols were enantioselectively synthesized using biotransformations as the key steps. They were used as ligand in the enantioselective borane reduction of acetophenone and of the corresponding anti oxime methyl ether.

Synthesis and structure of new chiral ferrocenylphosphines for asymmetric catalysis

Abstract The reaction of ( R )-1-[( S )-(diphenylphosphino)ferrocenyl]ethyl acetate ( 1 ) or N,N -dimethyl-( R )-1-[( S )-(diphenylphosphino)ferrocenyl]ethylamine ( 2a ) with secondary phosphines in acetic acid leads to the diphosphines 5 in moderate to good yields. Two of these ligands, ( R )=1[( S )-(diphenylphosphino)ferrocenyl]ethyl-dicyclohexylphosphine ( 5a ) and ( R P , R )-1[( S )-(diphenylphosphino)ferrocenyl]ethyl-phenyl-(2-methoxyphenyl)phosphine ( 5g ), as well as the complexes [Rh( 5a )(NBD)]BF 4 ·2CH 2 Cl 2 ( 9 ), [Pd(η 3 -C 3 H 5 ) ( 5a )]OTf ( 10 ) and [PtCl 2 ( 5a )] ( 11 ), have been characterized by X-ray diffraction. Crystals of 5a, 9, 10 and 11 are orthorhombic, space group P 2 1 2 1 2 1 , with four molecules in the unit cell. 5a : a =10.772(1), b =15.278(1), c =21.069(2) A; 9 : a =18.166(2), b =17.540(2), c =14.564(1); 10 : a =10.995(4), b =14.021(8), c =25.410(11) A; 11 : a =15.077(14), b =15.122(16), c =16.188(11) A. The stereogenic-at-phosphorus derivative 5g crystallizes in the monoclinic system, space group P 2 1 , with two pairs of symmetry independent molecules per the unit cell with a =7.896(1), b =25.667(2), c =15.654(1) A and β=92.39(1)°. Very similar conformations of the chelate rings in the complexes 9–11 are observed, this being indicative of the relative rigidity of the ligand 5a .

Studies on organophosphorus compounds—XLI: Formation of 3-pyrazoline-5-thione disulfides from 3,5-pyrazolidinediones. C-alkylation of 3,5-pyrazolidinediones

Abstract 4-Substituted-1,2-diphenyl-3,5-pyrazolidinediones (Phenylbutazone analogous) 1a–d react with 2,4-bi-(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-difulside (Lawesson Reagent (LR) with formation of the corresponding 3,3′-dithiobis (1,2-dihydro-3 H -pyrazole-5-thione)s 2a–d . When the 4-substituent contains a sulfoxide group this is deoxygenated to the sulfide by LR at room tmeperature. 1-Phthalazinone-4-thione, 1,4-phthalazine-dithione and ethyl aminothioxoacetate have also been prepared from the corresponding carbonyl compounds. Alkylation or acylation of 2a–d yielded 3H-pyrazole-3-thione derivatives 8 and 9 . Alkylation of 1 with MeI in the presence of Et 3 N at room temp. yielded the C-alkylated products 10 exclusively. X-RAy crystallographic investigations of 2b and 9a are presented.

Fluorine-containing organozinc reagents. II: The crystal structure of (1,1-dichloro-2,2,2-trifluoroethylzinc chloride)•2(dimethylformamide)

Abstract The DMF complex of 1, 1-dichloro-2, 2, 2-trifluoroethylzinc chloride, a key intermediate in the one pot synthesis of CF 3 CCl 2 -substituted alcohols, has been isolated and its structure determined by 13 C NMR spectroscopy and by X-ray diffraction. This is the first X-ray structural study of a perhalogenated alkylzinc halide and the results show the DMF complex to be monomeric.

A new electrophilic 2-pyrone bearing a CF3-group, its preparation and its [4+2] cycloaddition reactions

Abstract An efficient method for the synthesis of 4-methoxycarbonyl-6-trifluoromethyl-2H-pyran-2-one (4) starting from the 1:1-adduct of the CuCl-catalysed addition of 1,1,1-trichloro-2,2,2-trifluoroethane to dimethyl itaconate is presented. The new electrophilic 2-pyrone 4 affords [4+2] cycloadducts with a number of olefins and acetylenes. Their formation follows the reactivity patterns of a typical Diels-Alder reaction with inverse electron demand. The overall sequence represents a new methodology for the transfer of the CF3- group from a simple freon into more complex organic compounds.

Enantioselective synthesis: Catalysis of the aldol reaction by neutral gold(I)-chiral ferrocenylphosphine complexes. Crystal structure of the complex [{(η5-C5H4PPh2)(η5-C5H3(PPh2)CH(Me)N(Me)CH2CH2NMe2)Fe}2(AuCl)3] · Et2O

Abstract The chiral aminoferrocenylphosphine [(η 5 -C 5 H 4 PPh 2 )(η 5 -C 5 H 3 (PPh 2 )CH(CH 3 )-N(CH 3 )CH 2 CH 2 N(CH 3 ) 2 )Fe] ( 1 ) reacts with (H 3 C) 2 SAuCl to give neutral gold(I) complexes that are active catalysts for the enantioselective coupling of isocyanoacetate esters with aldehydes, forming dihydrooxazoles. The structure of the trimeric complex [(rac- 1 ) 2 (AuCl) 3 ] · Et 2 O has been determined by X-ray diffraction.

The azo-chromophor as component in photo [2+2]-cycloaddition reactions synthesis, structure and pe-analysis of planar-parallel bisazo-molecules

Abstract In order to test for a photo [2+2]-cycloaddition between two azo-units a tetracyclic bisazo-compound (7) has been constructed, for which the X-ray analysis confirms a planar-parallel arrangement of the N 2 -units and transannular N-N-distances of 2.877 A and 2.821 A, resp. In preliminary photoexperiments N 2 -elimination predominates in 7; in the N-oxides 10/11, however, after direct excitation (λ = 254 nm) N 2 /N 2 O-metathesis (13/14 and 15, resp.) is observed.

Cladospirone bisepoxide: Definite structure assignment including absolute configuration and selective chemical transformations

Abstract The definite structure of cladospirone bisepoxide 1 was determined as 1a by X-ray analysis. The absolute configuration could be deduced from the X-ray crystallographic structure determination of its ring-opened product 8 . In order to define the structural features responsible for various biological effects of this metabolite, the reactivity of the epoxide and enone functional groups has been explored.