Thermische Umlagerungen von (+)-Isopinocampheol und (−)-Isopinocamphon

Short-path thermolysis of (+)-isopinocampheol ( 1 ) at about 330° in the gas phase yields mainly (—)-(3 S, 4 S)-3, 7-dimethyl-octa-1,6-dien-4-ol ( 2 ). Longer heating of 2 at about 290–330° yields as main products the diastereoisomeric hydroxy-Δ⁸-iridenes 3, 4 and 5 in ratios dependent on temperature. Above 400°, formation of 4-methylpent-3-en-1-al ( 7 ) and 2-butene ( 8 ) predominates. Compounds 7 and 8 also appear as the stable final thermolysis products of 3, 4 and 5 above 500°. Small quantities of (+)-iso-dihydrocarveol ( 6 ) always occur as by-product in the thermolysis of 1 . Short-path thermolysis of (—)-isopinocamphone ( 13 ) at about 430° leads, with slight epimerisation, to the three diastereoisomeric oxo-Δ⁸-iridenes 15, 18 and 17 via (+)-(3 S)-3, 7-dimethylocta-1, 6-dien-4-one ( 14 ). Structure and stereochemistry of all reaction products are established spectroscopically and chemically.     

Chinolizine und Indolizine,XIV Umlagerungen von Heterocyclen,X Ringumwandlungen von 1-Acyl-2-hydroxy-4-chinolizinonen

By heating with ammonia or aniline 1-acyl-2-hydroxy-4-quinolizinones (1 a–e) are transformed to 4-hydroxy-5-(2-pyridyl)-2-pyridones (3 a–f), with4 a–d as minor sideproducts. The structure of the rearranged compound3 f was established by an independent synthesis starting with6 and7. The reaction of1 a, d with ethyl β-aminocrotonate (β-ACE) yields pyrono-quinolizinones8 a, b and pyronopyridones9 a, b as byproducts; the latter are obtained in high yield by reaction of3 a, b with β-ACE. The ringtransformation reaction cannot be extended to 1-methoxycarbonyl-quinolizinones, such as10; in this case 2-amino-4-quinolizinone11 is the main product of the reaction with ammonia.     

Thermische Umlagerungen von halogensubstituierten Aryl-propargyläthern

7-Chloro-2-chloromethyl-benzofuran (13) and 3, 8-dichloro-2 H-1-benzopyran (12) are the main products from the thermal rearrangement (230–260°) of 2, 6-dichlorophenyl propargyl ether (7) . Compounds 17 , 18 and 19 are also formed, but in much smaller amounts (scheme 2 and table 1). However, in the case of the bromo-compounds 8 and 9 the rearrangement products are the benzofuran derivatives 21 and 22 , containing one bromine atom less per molecule (scheme 4). The corresponding naphthyl propargyl ethers 10 and 11 can be rearranged much more easily (180°) to the halogeno-naphthofurans 24 and 26 respectively. In the case of the bromo-ether 11 , 2-methyl-naphtho[2, 1-b]furan (25) is also formed (scheme 5). If the propargylic hydrogen atoms in 7 and 11 are replaced by deuterium atoms, then after rearrangement the deuterium atoms in the products d- 13 and d- 26 are found in the β-positions to the oxygen atom of the furan ring (schemes 3 and 5). It is suggested that initially a [3s, 3s]-sigmatropic rearrangement of the aryl propargyl ethers to the 6-allenyl-6-halogeno-cyclohexa-2, 4-dien-1-ones (e.g. a ) occurs and that from these the isolated products are formed via radical pathways (scheme 6). Under neutral conditions aryl propargyl ethers containing a free ortho-position give on heating benzopyran derivatives [2]. When this thermal reaction is carried out in sulfolane in the presence of powdered potassium carbonate, 2-methyl-benzofuran derivatives are formed (table 2). This leads to the possibility of preparing, depending on the conditions, either benzopyran or benzofuran derivatives by the Claisen rearrangement of aryl propargyl ethers. The mechanism for the formation of the benzofurans is given in scheme 9.