Rearrangement of Cephem Bromohydrins to Thiazepine Derivatives

A new rearrangement of cephem bromohydrins 2 – 5 to thiazepine derivatives 7 – 8 is described. The structure of the rearrangement product is established by an independent synthesis. The probable mechanism of the above rearrangement is discussed.     

Total synthesis of (-)-okilactomycin

A highly convergent synthesis of (-)-okilactomycin is described. Key reactions of this synthesis include a strategy-level diastereoselective oxy-Cope rearrangement/oxidation sequence, a Petasis-Ferrier union/rearrangement tactic, and an efficient RCM reaction to construct the 13-membered macrocyclic ring.     

Development of the 1,2-oxaza-Cope rearrangement

A method for a concise assembly of oxazine rings based on a Lewis acid-promoted hetero-Cope rearrangement is described. The hetero-Cope rearrangement features the first examples of the [3,3]-sigmatropic transpositions involving the nitroso group. A variety of functionalized substrates have been subjected to the reaction. The described method has a strong potential for the synthesis of marine natural products containing oxazine rings.     

A cyclobutene bridgehead olefin approach to the germacranes

A model study for the synthesis of the germacranes is described which utilizes a consecutive oxy-Cope/cyclobutene ring opening rearrangement sequence. The β,γ-unsaturated enone necessary for the rearrangement is obtained directly from the photocycloaddition of allene and cyclohexenone.     

Solvent effect in the synthesis of 4-carbamoyl-3-hydroxycoumarins

A new synthesis of 4-carbamoyl-3-hydroxycoumarin is reported. The synthesis of carbanilates of 3-hydroxycoumarin and their novel rearrangement to the carboxamides is also described.     

Lewis acid-mediated unprecedented ring-opening rearrangement of 2-aryl-N-tosylazetidines to enantiopure (E)-allylamines

A highly efficient strategy for Cu(OTf)2-mediated ring-opening of 2-aryl-N-tosylazetidines in polar and coordinating solvents followed by an unprecedented rearrangement to substituted achiral and chiral (E)-allylamines (ee >99%) is reported. The methodology has been applied for the synthesis of gamma-unsaturated-beta-amino acids. A plausible mechanism for the rearrangement is also described.     

A biomimetic type expedient approach to the tricyclic core of xyloketals. Application to a short, stereocontrolled synthesis of alboatrin and a remarkable epi to natural isomerisation

An expedient synthesis of the linear tetrahydrofurano benzopyran ring system of xyloketals is described involving an ortho ester Claisen rearrangement and an intramolecular cationic cyclisation. This strategy was applied for a short, stereocontrolled and high yield synthesis of the phytotoxic metabolite alboatrin.     

A short and efficient synthesis of furo[2,3-b]indoles

Application of Wittig olefination-Claisen rearrangement protocol for the short synthesis of furo[2,3-b]indoles is described.     

Regioselective two step synthesis of 3-substituted 2-aminoimidazo[1,2-a]pyrimidines

A two step procedure for the regioselective synthesis of 3-substituted-2-aminoimidazo[1,2-a]pyrimidines is described. The key step is a Dimroth rearrangement of a mixture of 2 and 3-substituted aminoimidazo[1,2-a]pyrimidines that yields quantitatively one regioisomer. Reaction screening for the rearrangement step is reported. A multicomponent isocyanide based reaction is chosen as the preferred way for the synthesis of the precursors. Elucidation of regiochemistry has been done by X-ray determination of some representative compounds.     

Formal total synthesis of (±)-magellanine

Formal total synthesis of magellanine is described. Key features in the synthesis were stereoselective Ireland-Claisen rearrangement and intramolecular Pauson-Khand reaction of exo-cyclic enynes.     

Application of directed metalation in synthesis. Part 6: A novel anionic rearrangement under directed metalation conditions leading to heteroannulation

A short and efficient synthesis of condensed 1,4-oxathiin-2-ones from easily available phenols is described. The key step in this synthesis is a hitherto unreported anionic rearrangement under directed metalation conditions. The rearrangement occurs after side chain deprotonation of a methyl sulfanyl group by an O-carbamate directed metalating group and the reaction mixture is kept at room temperature for 8-12 h. Acid-mediated cyclisation of the rearranged product affords [1,4]oxathiin-2-one.     

Synthesis of novel spiro-cyclohexene bicyclo[2.2.2]octane derivatives

A methodology for the synthesis of novel spiro-cyclohexene bicyclo[2.2.2]octane derivatives, including Claisen rearrangement and ring-closing metathesis (RCM) as key synthetic steps, is described.     

1-Alkynyl Disulfides: Their Characterization and Their 1-Thiapropargyl — 3-Thiaallenyl Rearrangements

The synthesis of novel 1-alkynyl disulfides 1 is described together with their 1-thiapropargyl — 3-thiaallenyl rearrangement and a [1,3]-sigmatropic shift of 1-alkynyl amino disulfides, followed by rearrangement of the aminothio-substituted thioketenes so formed.     

Synthesis of 2-cyclopentenones by gold(I)-catalyzed Rautenstrauch rearrangement

The rearrangement of 1-ethynyl-2-propenyl pivaloates to cyclopentenones catalyzed by cationic triphenylphosphinegold(I) complexes is described. The reaction tolerates both alkyl and aryl substitution at the acetylenic and olefinic positions. Importantly, the gold(I)-catalyzed rearrangement of enantioenriched propargyl pivaloates proceeds with excellent chirality transfer, thus providing a practical method for the enantioselective synthesis of cyclopentenones.     

Deamination of 6-aminopenicillanic acid

The synthesis of 6α-acyloxy-penicillanic acids either by deamination of 6-amino-penicillanic acid or by rearrangement of N-nitroso-penicillins is described.     

Formal synthesis of (+)-crocacin C

The formal synthesis of (+)-crocacin C is reported. The approach described takes advantage of a highly regioselective epoxide cuprate addition and a diastereoselective Overman rearrangement. The synthesis is practical and amenable to scale up.     

Synthesis of 2-amino-3-methoxypyrazinc

A new synthesis of 2-amiuo-3-methoxypyrazine, an intermediate in the synthesis of sulfalene, via 2-carbamido-3-hydroxy pyrazine and subsequent Hofmann rearrangement of 2-carhamido-3-methoxypyrazine, is described.     

Stereocontrolled synthesis of conjugated dienamides via the ynamine-claisen rearrangement with (arylthio)ynamine

A new, versatile method for the stereocontrolled synthesis of conjugated (E, E)-dienamides is described which relies upon the acid-catalyzed or thermal ynamine-Claisen rearrangement with readily accessible (arylthio)ynamines.     

Reaction of Oximes of α-Diketones with Diphosphorous Tetraiodide for Preparation of Oxadiazoles and Nitriles

The utility of diphosphorous tetraiodide as a new, mild, condensing agent for synthesis of oxadiazole is described. These data indicate the simple dehydration of oximes to 1,2,5-oxadiazole as well as the rearrangements of oximes to normal Beckmann product 1,2,4-oxadiazole. However, mono-oxime of benzil undergoes abnormal Beckman rearrangement to benzaldehyde as major product. The described method is simple and important for the synthesis of the oxadiazoles as well as for nitriles.     

Asymmetric synthesis of chiral synthons bearing alkynyl group via organoaluminum-promoted pinacol-type rearrangement

A method is described for the synthesis of chiral alkynyl ketones and alkynols via trimethylaluminum-promoted pinacol-type rearrangement where alkynyl groups behave as “the staying group”, followed by stereoselective reduction leading to the latter.