Application of the gold(I)-Catalyzed aldol reaction to a stereoselective synthesis of (2S, 3R, 4R, 6E)-3-Hydroxy-4-methyl-2-(methylamino)oct-6-enoic Acid ( = MeBmt), Cyclosporin's unusual amino acid

The title compound 8 was prepared in three steps starting from the optically pure aldehyde (2R, 4E)-2-methyl-hex-4-enal ( 3 ), thus constituting the shortest synthetic approach reported. Two of the three stereogenic centers in the product were generated in a coupling reaction of 3 with ethyl isocyanoacetate, catalyzed by a gold(I)/chiral ferrocenylphosphine system, giving the dihydrooxazole 5 in 85% diastereoselectivity (mismatchedcase). The weak effect of double stereodifferentiation in this reaction (matched case 90% ds) is discussed. N-Methylation and hydrolytic ring opening of 5 gave the protected form 7 of MeBmt, The X-ray diffraction study carried out on 7 confirms the absolute configuration of the two stereogenic centers formed in the gold(I)-catalytic reaction.     

Monocarboxylates of 3-Methylidene-β-lactams: Synthesis and unusual oxidative rearrangement into a spiro[azetidine-3,3′-pyrrolidine] derivative

Reaction of the 3-silylated β-lactams 1 with glycoxalates gives bis-lactam 3 , but the same reaction in the presence of 1 equiv. of Me₃SiCl leads to the formation of the disilylated adducts 5 . The latter is desilylated by (Bu₄N)F yielding the monocarboxylates 7 of 3-methylidene-β-lactams, which, with oxidizing agents, give the spiro compound 8 . The structure of 8 is established by spectroscopic data and a crystal-structure analysis.     

Isomerization of the azo-group in a tetrahydro-thiadiazepine

The preparation, isomerization and decomposition of the cis and trans isomer of a heterocyclic azo-compound is described.     

3,4,9,10 - Tetrathioperylene - I1.28, a new highly conducting,incommensurate organic charge transfer salt

We report here the preparation of TTP - I_1.28 (TTP = 3,4,9,10 - Tetrathioperylene), the crystal structures of TTP and its complex TTP - I_1.28 and their electrical conductivities. The crystal structure of TTP consists of two inequivalent types of segregated stacks with intermolecular planar spacings of 3.43 Å, and 3.47 Å. The crystal structure of TTP - I_1.28 consists of two incommensurate sublattices. The TTP sublattice is built up by segregated stacks of TTP molecules with interplanar spacing of 3.25 Å. The iodine sublattice consists of columns formed mainly by I₃ units. The electrical conductivity is very weakly metallic at room temperature and turns to a semiconducting behavior at 220 K with an activation energy of 15 meV.     

The Thermal Reactivity of 5,8α-Epidioxy-5α-cholestan-3β-yl Acetate in Acetic Acid

The thermolysis of the steroidal 5α,8β-peroxide 1 , under acidic conditions afforded in addition to the expected 5,10:8,9-diseco derivative 2 , the rearranged 5α,8β-epoxide 3 , the structure of which was determined by NMR spectroscopy and X-ray analysis.     

Electrical Double-Layer Structure at the Rutile-Water Interface as Observed in Situ with Small-Period X-Ray Standing Waves

X-Ray standing wave (XSW) measurements were made of Rb and Sr adsorbed from aqueous solutions at the rutile (110)-water interface. These experiments were performed to address the extent to which direct measurements of electrical double-layer structure are possible. The experimental results show that the Bragg XSW technique, using small-period standing waves generated by Bragg diffraction from the substrate, can precisely measure ion locations within the condensed layer and the in situ partitioning of ions between the condensed and diffuse layers. Differences in condensed layer ion positions were observed for Sr ions (measured in situ) as compared with Rb ions (in situ) and also for Sr ions (ex situ). An additional constraint on the ex situ Sr site geometry was provided by polarization-dependent surface EXAFS measurements. Such measurements can provide important constraints for the development and verification of electrical double-layer theory especially as applied to ion adsorption at the solid-water interface. Copyright 2000 Academic Press.     

5,10:8,9-Disecosteroids (= Steroklastanes): A new type of modified steroids

Thermolysis of steroidal 5α, 8α- peroxides of type 3a-d generates as major products the corresponding diseco compounds containing a 14-membered ring instead of the standard A-B-C-ring skeleton. Depending on the reaction conditions, either the primary products of type 9 or the α, β-unsaturated ketones of type 4 , formed by subsequent elimination of AcOH, are isolated. The latter, configurationally uniform compounds undergo epoxidation of the C(9)=C(10) bond followed by a Baeyer-Villiger oxidation to give, as final products, the 15-membered cyclic epoxyenol lactones of type 20 and 21 . The structures of the various products were determined by ¹H- and ¹³C-NMR spectroscopy. The conformations of the 14- and 15-membered rings were established by X-ray structure analyses of 7 and 21a . A reaction mechanism for the above transformations is discussed.