Thermal behaviour of aryl γ-haloprcpargyl ethers

An alternative method for the regio- and stereoselective bromination of alkenes, alkynes, toluene derivatives and ketones using a bromide/bromate couple

Abstract: Mixtures of NaBr and NaBrO3 in two different ratios have been used for highly stereoselective bromination of alkenes and alkynes, and regioselective bromine substitution at the α-carbon of ketones and at the benzylic position of toluene derivatives. The reactions were conducted in an aqueous acidic medium under ambient conditions. The solid reagents were prepared from the intermediate obtained in the “cold process” of bromine manufacture and are stable, non-hazardous and inexpensive to prepare. This procedure provides an efficient and practical alternative to conventional procedures using liquid bromine directly or indirectly.

Ruthenium-catalyzed [2 + 2] cycloadditions between bicyclic alkenes and alkynyl halides.

Abstract: Ru-catalyzed [2 + 2] cycloadditions between norbornadiene and alkynyl halides were found to occur in moderate to good yields (32−89%). The presence of the halide moiety greatly enhances the reactiv...

Alkynyl Halides in Ruthenium(II)-Catalyzed [2+2] Cycloadditions of Bicyclic Alkenes

Abstract: Ru-catalyzed [2+2] cycloadditions between bicyclic alkenes and alkynyl halides were found to occur in moderate to good yields. The presence of the halide moiety greatly enhances the reactivity of the alkyne component in the cycloaddition and can be transformed into a variety of products that are difficult or impossible to obtain by direct cycloaddition. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Rhodium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides.

Abstract: Cationic rhodium(I)-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were found to occur in good yields (70−87%). The halide moiety is compatible with the cycloaddition reactions, and no oxidative insertion to the alkynyl halide was observed. The halogen-containing cycloadducts could be transformed into a variety of products that are difficult or impossible to obtain via direct cycloaddition.

Claisen rearrangement of aryl propargyl ethers in poly(ethylene glycol)- a remarkable substituent and solvent effect

Abstract: The Claisen rearrangement of aryl propargyl ethers in poly(ethylene glycol) - 200 at 200°C affords products in good yields. Aryl propargyl ethers containing electron donating groups yield (2H)-benzopyrans and those containing electron withdrawing groups yield 2-methylbenzofurans.

A simple route for the synthesis of 4-chlorochromenes and chroman-4-ones

Abstract: A one pot synthesis of a number of 4-chlorochromenes and chroman-4-ones was achieved from γ-chloropropargyl aryl ethers proceeding through Claisen rearrangement, depending upon the solvent of choice.

Claisen-Umlagerung von 2-Propinyl-(3-pyridyl)-und Allyl-(3-pyridyl)äthern†

Abstract: Claisen Rearrangement of 2-Propinyl (3-Pyridyl) and Allyl (3-Pyridyl) Ethers1 2-Propinyl (3-pyridyl) ether (1), synthesized from the corresponding 3-pyridinol, was heated in DMF or decane at 208° in a sealed tube. In this way the furopyridines 2 and 3 were formed, and furthermore the pyranopyridine 4 if decane was used as solvent (Scheme 1). The same reactions took place with (2-methyl-3-pyridyl) 2-propinyl ether (14). In DMF only 15, and in decane 16 as well as 15 were formed (Scheme 3). The rearrangement of the pyridine derivative 17, which is substituted in both O-positions to the ether moiety, gave in both DMF and decane the diastereoisomeric tetracyclic compounds 18 and 19. The same kind of reaction took place with 25 (Scheme 4). In the thermolysis of the allyl 3-pyridyl ether (27) cyclization was observed, too. The isolated product has the structure of the dihydrofuropyridine 28 (Scheme 6). The substituted allyl 3-pyridyl ether 30 reacted in the same way to the dihydrofuropyridine 31 (Scheme 6).

Synthese und Eigenschaften der 4‐Chlor‐ und 4‐Brom‐2H‐chromene sowie der 3‐Brom‐2H‐chromene

Abstract: Durch Abspaltung von Bromwasserstoff entstehen aus den trans-3.4-Dihalogen-chromanen die entsprechenden 4-Halogen-2H-chromene 1–4. Die 3-Brom-2H-chromene 5 und 6 erhalt man durch Dehydratisierung der cis-3-Brom-4-hydroxy-chromane. Synthesis and Properties of 4-Chloro- and 4-Bromo-2H-chromenes and of 3-Bromo-2H-chromenes Dehydrobromination of trans-3,4-dihalochromans yields the 4-halo-2H-chromenes 1–4. Dehydration of cis-3-bromo-4-hydroxychromans leads to the 3-bromo-2H-chromenes 5 and 6.