The orbital sequence in cyclic 1,3-diketones

The He(I) photoelectron (PE) spectra of the cyclic 1,3-diketones 1–5 have been recorded. Based on a comparison between experimental and calculated (MINDO/3) results it is shown, that in all cases the n_(A) orbital is on top of the n₊(S) orbital. This sequence is confirmed by the comparison between the PE spectra of 1–5 with those of the corresponding vic.triketones 6–10.     

The cycloacylation — 1,3‐Acylrearrangement sequence as tool for highly substituted pyrrolones

The cyclization reactions between bis‐imidoylchlorides 1 and ketones, which possess different CH‐acidity, were investigated. Diphenylacetone 2 reacts under mild conditions via C,O‐cyclization of the preformed enolate to yield the iminofurane derivative 3 . Upon treatment with trifluoroacetic acid, the latter can be rearranged quantitatively into the pyrrolone 5 . In contrast, 1,3‐acetonedicarboxylate 9 and cyclohexanone 12 immediately lead to highly substituted pyrrolones 11 and 14 . Obviously, the primarily formed cyclization products undergo a very fast 1,3‐acyl rearrangement (Dimroth‐/Mumm‐Rearrangement). The structures of the maleiimide 11 and the indolone 14 were determined by single crystal X‐ray structure analysis. Due to its amino/imino substructure, compound 3 is an efficient ligand for metal complexation reactions, exemplified by the synthesis of two different Zn‐complexes 7 and 8 .     

Synthesis of spiro-substituted 1,3-oxazines by a new sequence leading to spiroheterocycles

Summary The target compounds, i.e. 1,3-oxazines which are spiro-substituted in position 6 by a piperidine moiety, are derived from 1-oxa-3,9-diaza-spiro[5.5]undecane, a novel heterocyclic parent system. They were all approached by the following three-step sequence: 1,3-dipolar cycloadditions of nitrile oxides and nitrones to piperidines bearing an exocyclic methylene group gave the corresponding spiro-substituted oxazole derivatives3. In a consecutive step these were cleaved by hydrogenolysis to -amino-alcohols4, which in a final step were recyclized by insertions of a C₁-unit to yield the target structures5–10: thus ade facto ring-extension of spiro-oxazoles to spiro-oxazines was accomplished.

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Synthese von spirosubstituierten 1,3-Oxazinen mittels einer neuen zu Spiroheterocyclen führenden Synthesefolge

Zusammenfassung Die Zielverbindungen, d.h. 1,3-Oxazine mit einem Piperidinring als Spiro-Substituenten in 6-Stellung, leiten sich von 1-Oxa-3,9-diaza-spiro[5.5]undecan, einem neuen heterocyclischen Grundkörper, ab. Sie wurden alle mit Hilfe der folgenden dreistufigen Synthesefolge zugänglich gemacht: 1,3-dipolare Cycloadditionen von Nitriloxiden und Nitronen an Piperidinderivate mit einer exocylischen Methylengruppe gaben die entsprechenden spiro-substituierten Oxazolderivate3. Diese wurden anschließend hydrogenolytisch zu den -Aminoalkoholen4 gespalten, welche schließlich wieder unter Einschub von einem C-Atom zu den Zielstrukturen5–10 cyclisiert wurden: dadurch wurde einede facto-Ringerweiterung von Spiro-Oxazolen zu Spiro-Oxazinen erreicht.

     

The methoxycarbonylcarbene insertion into 1,3-dithiolane and 1,3-oxathiolane rings

Treatment of substituted 1,3-dithiolanes and 1,3-oxathiolanes with methyl diazoacetate in the presence of Rh₂(OAc)₄ effects ring expansion to the corresponding substituted 1,4-dithiane-2-carboxylates and 1,4-oxathiane-3-carboxylates. The sulfur ylides initially generated in these reactions undergo Stevens rearrangement in competition with both [2,3]-C-C-sigmatropic rearrangement and intramolecular fragmentation. In the case of 2-styryl-substituted 1,3-oxathiolane and 1,3-dithiolane, ring expansion on one-, three- and four-carbons subsequently takes place.     

Synthesis of 1,3-diarylsubstituted indazoles utilizing a Suzuki cross-coupling/deprotection/N-arylation sequence

Herein we report a general synthesis of 1,3-diarylsubstituted indazoles utilizing a two-step Suzuki cross-coupling/deprotection/N-arylation sequence. This procedure proceeds in excellent overall yield starting from the 3-iodo-N-Boc indazole derivative allowing for rapid access to these compounds.     

The vibrational spectra of some 1,3-dimethyl-1,3-diaza-2-boracyclopentanes

A detailed vibrational assignment is proposed for 1,3-dimethyl-1,3-diaza-2-boracyclopentanes:

where X = Cl, Br or NMe₂. The assignments are generally in accord with C_2v symmetry, but there is some evidence for a slight breakdown, as some A₂ modes appear in the IR. The BN₂ stretches are near 1500 cm^?1, (antisymmetric) and 1300 cm^?1 (symmetric), consistent with a large degree of π-bonding.     

The synthesis of 1,3-diamidophospholipids

A straightforward synthesis of a small library of 1,3-diamidophospholipids is presented using readily available, cheap reagents and introducing a simple phosphoramidate protecting group strategy.     

Substituted propanes: VI. The vibrational spectra and conformations of 1,3-dichloro-, 1,3-bromochloro-, 1,3-dibromo- and 1,3-diiodo-propane

The infrared and Raman spectra of 1,3-dichloro-, 1,3-bromochloro-, 1,3-dibromo- and 1,3-diiodopropane were recorded as liquids and in the crystalline state at low temperatures. Crystals of 1,3-dibromo- and 1,3-diiodopropane formed under ca. 20 kbar pressure at ambient temperature were studied by infrared technique.No evidence was found for the GG₁ conformer (parallel C-halogen bonds), but the other three staggered conformers (GG, AA, and AG) (four for 1,3-bromo-chloropropane) were observed in the liquid. In all the stable low temperature crystals the GG conformers were present, at high pressure 1,3-dibromopropane crystallized in GG and 1,3-diiodopropane in the AA conformation. The C-halogen stretching vibrations have been interpreted in detail. A complete list of fundamentals have been proposed for the GG conformers in each compound, for 1,3-diiodopropane the additional AA fundamentals have been assigned whereas some AG bands were interpreted for each compound.     

1,3-Dimethoxy-1,3-dimethyl-1,3-diphenyl- and 1,3-dimethoxy-1,3-tetraphenyldisiloxanes: synthesis and structure

Russian Chemical Bulletin - 1,3-Dimethoxy- 1,3-dimethyl- 1,3-diphenyl- and 1,3-dimethoxy- 1,3-tetraphenyldisiloxanes were synthesized. Their structures were confirmed by IR and NMR spectroscopy....     

The anomeric effect in 2-arylseleno-1,3-dithianes

The anomeric effect in a series of 2-(4-substituted-phenylseleno)-1,3-dithianes (substituents, R = NO₂, CF₃, H, OMe, NMe₂) decreases in the sequence NO₂>CF₃>H>OMe>NMe₂, providing systematic experimental evidence for the role of stabilizing orbital interactions.     

1,3-Migration of Hydrogen in 1,3-Dioxane Carbocation

Russian Journal of Organic Chemistry -     

The sequence length in polymethyl methacrylate

The sequence length and tacticity of methyl methacrylate polymers prepared at 303–363°K in the presence of trichlorobromomethane as a transfer agent were measured from NMR spectra. The lengths did not change appreciably but there was an increase in syndiotacticity with increasing concentration of transfer agent. There is no marked change in tacticity with molecular weight.     

The Dielectric Properties of 1,3-Butanediol

The dielectric properties of 1,3-butanediol were measured over the temperature range 293–423 K. The static permittivity ε_s was measured at a frequency of 1 MHz. The permittivity ε′ and dielectric loss ε′’ were determined by the balance method over the frequency range 2–37.5 GHz.