Type C rearrangement

Finally, it should be mentioned that as early as 1974 a combination of this rearrangement with the Type C rearrangement followed by a Ramberg-Bficklund olefination [91] was used to synthesize a number of trienes... 

Scheme 40 Combined application of Type H and Type C rearrangements for the synthesis of trienes...

With knowledge that 7i-bond twisting is a factor in leading to the Type C rearrangement, we turned to study the 3-t-butylcyclohexenone 52 in Scheme 8.13. The introduction of... 

Table 8.14 Computational Results for the Enone 52 Type C Rearrangement Species ...

The important application of the type C rearrangement is demonstrated by the synthesis of 4-hydroxy-2-cyclopentenone, a prostaglandin intermediate, starting from cyclopentadiene (Scheme 6)J"... 

The 1-oxide 3-oxide tautomerism [Eq. (3), p. 4] has been discussed earlier (Sections II and III,C) in connection with the problem of the structure of benzofuroxan. A second type of rearrangement involves the furoxan ring and an adjacent substituent group, and arose out of a suggestion of Bailey and Case that 4-nitro-benzofuroxan might be a resonance hybrid of type (57)-(-> (58), rather than 57. NMR ruled out this possibility the three protons present in... 

Sulfur and selenium analogues of 91 are also susceptible of this type of rearrangement. Its rate is defined by the strength of the C-chalcogen bonds in 91 and analogues and was found to increase in the order of S < Se < Te (94MI1). 

Thermal rearrangement of 2-vinylaziridines yields 3-pyrrolines. When aziri-dines 192 were heated in decalin at 180 °C, 3-pyrrolines 193 were formed in 75-85% yields (Scheme 2.48) [75]. A similar rearrangement was also observed by Lwowski and coworkers [4]. This type of rearrangement can be effectively pro-... 

The pseudobenzylisoquinoline alkaloids are fairly widespread in nature, being found among members of Berberidaceae, Annonaceae, Fumariaceae, and Ranunculaceae. The biogenesis of the pseudobenzylisoquinoline alkaloids assumes their formation from protoberberinium salts by C-8—C-8a bond scission in a Baeyer-Villiger-type oxidative rearrangement to produce the enamides of type 73 and 74. These amides may be further biotransformed either to rugosinone (76) type alkaloids by hydrolytic N-deformylation followed by oxidation or to ledecorine (75) by enzymatic reduction. These transformations were corroborated by in vitro studies (80-82). It is suggested that enamide seco alkaloids may be precursors of aporphine alkaloids (80), on one hand, and of cularine alkaloids (77), on the other. 

If the insertion step following oxidative addition occurs on one of the two fragments resulting from oxidative addition, an intramolecular catalytic reaction (C—O — C—C rearrangement) takes place (example 40, Table III). It is interesting to note that two different products—2,6- and 3,6-heptadienoic acids—can be obtained from allyl 3-butenoate. Their ratio can be controlled by adding 1 mole of the appropriate phosphine or phosphite to bis(cyclooctadiene)nickel or similar complex. Bulky ligands favor the 2,6 isomer. It is thus possible to drive the reaction toward two different types of H elimination, namely, from the a or y carbon atoms. 

Scheme IV.3). The general scheme of this type of rearrangements in aromatic five-membered heterocycles with an unsaturated side chain is known as the Boulton-Katritzky rearrangement [67JCS(C)2005]. 

Another type of rearrangement, involving ring-contraction of the seven-membered ring, occurs when c/s-2,3-diphenyldihydrodiazepine is heated above its melting point 2,3-diphenylpyridine and ammonia are formed... 

From a study of his and van Alphen s results, Huttel identified three classes of rearrangement (Scheme 40).137 Type A involved migration of a group from C-3 to unsubstituted C-4 (e.g., 114 - 11564), Type B an acyl migration from C-4 or C-5 to N (e.g., 116 -> 11764or 118 - 117137), and Type C an aryl migration from C-3 to N (e.g., 118 - 119137) the latter two modes were observed when all carbon atoms were fully substituted. 

Phosgenimium chlorides (585) permit a regiospecific synthesis of 3-(di-substituted amino)triazolo[4,3-c]pyrimidines (588) from the 4-hy-drazinopyrimidine 488 without a Dimroth type of rearrangement... 

Treatment of the chroman-4-one 1 with benzyl chloride in DMF at 100°C gave the corresponding benzyl ether 2. When the reaction temperature was raised to 153°C, however, the products obtained were the chromone 3 and the flavone 4. It was subsequently shown that the same type of rearrangement could be effected simply by heating 1 with benzyl chloride in DMF containing potassium carbonate. 

In some cases at higher decomposition temperatures (above 100 °C), isothiocyanates 11 may be formed after concerted Curtius-type decomposition/rearrangement of a (Z)-thioacyl azide 10-Z, while the corresponding ( )-isomer would give the nitrile 12 in a Grob-like fragmentation. The nitrenes are formed after nitrogen extrusion from the thioacyl azides, which are the open-chain isomers of the 1,2,3,4-thiatriazoles (Scheme 3). 

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