Rearrangements with

When hydrazobenzene, or 5ym-diphenylhydrazine, is warmed with acids, it undergoes an intramolecular rearrangement, with the formation of benzidine,... 

When benzii is heated with potassium hydroxide solution, it undergoes a molecular rearrangement with the formation of the potassium salt of benzilic acid, or diphenyl lycollic acid ... 

Diallylsulfonium salts undergo intramolecular allylic rearrangement with strong bases to yield 1,5-dienes after reductive desulfurization. The straight-chain 1,5-dienes may be obtained by double sulfur extrusion with concomitant allylic rearrangements from diallyl disulfides. The first step is achieved with phosphines or phosphites, the second with benzyne. This procedure is especially suitable for the synthesis of acid sensitive olefins and has been used in oligoisoprene synthesis (G.M. Blackburn, 1969). 

Carboxylic acids react with butadiene as alkali metal carboxylates. A mixture of isomeric 1- and 3-acetoxyoctadienes (39 and 40) is formed by the reaction of acetic acid[13]. The reaction is very slow in acetic acid alone. It is accelerated by forming acetate by the addition of a base[40]. Addition of an equal amount of triethylamine achieved complete conversion at 80 C after 2 h. AcONa or AcOK also can be used as a base. Trimethylolpropane phosphite (TMPP) completely eliminates the formation of 1,3,7-octatriene, and the acetoxyocta-dienes 39 and 40 are obtained in 81% and 9% yields by using N.N.N M -tetramethyl-l,3-diaminobutane at 50 in a 2 h reaction. These two isomers undergo Pd-catalyzed allylic rearrangement with each other. 

A photochemical partial synthesis of aldosterone (19) made the hormone available on an industrial scale for the first time (114). Corticosterone acetate (51 acetate) is treated with nitrosyl chloride in pyridine at 20°C to yield the 11-nitrite (115). Irradiation of (115) leads to rearrangement with formation of the C g-oxime (116). Removal of the oxime residue with nitrous acid furnishes aldosterone (19) in excellent yield. 

Trialkyl phosphites participate ia Michaehs-Arbu2ov rearrangement with alkyl haUdes. Such esters can undergo auto-Arbu2ov rearrangement ia the absence of an alkyl haUde. 

Linalool can be converted to geranyl acetone (63) by the CarroU reaction (34). By transesterification with ethyl acetoacetate, the intermediate ester thermally rearranges with loss of carbon dioxide. Linalool can also be converted to geranyl acetone by reaction with methyl isopropenyl ether. The linalyl isopropenyl ether rearranges to give the geranyl acetone. 

Vkiyl aHenes (44) are rearranged with heat or metal catalysis and photosensitized isomerization to produce the vitamin D triene (156—160). 

Complexes involving larger metal clusters, eg, Au or Au2Rh, also undergo piezochromic rearrangements with rather dramatic changes in the absorption spectmm, and well-defined changes in molecular stmcture (6,7). 

Dibenzoyldiaziridine (130) thermally rearranges with ring opening and benzoyl migration to the dibenzoylhydrazone (138) (67CB142). 

Slgmatropic rearrangement with H-transler and C-C txjrxJ formation (inter or intramolecular) and chiral induction... 

The (9-isobomyl- and (9-[l-(5-pentamethylcyclopentadienyl)ethyl]-derivatives do not undergo rearrangement, but are very labile in trifluoroacetic acid (100% cleaved in 5 min). The cyclohexyl and isopropyl derivatives are more stable to acid, but undergo some rearrangement. The cyclohexyl group combines minimal rearrangement with ready removal. ... 

The contradictory observations that 16-dehydropregnenolone oxime fails to rearrange with phosphorus oxychloride while pregnenolone oxime undergoes the normal reaction " remain unexplained. The respective 3-acetates in both series rearrange in the expected fashion. 

An alkyl group can also migrate from oxygen to nitrogen or phosphorus [I, 72] (Michaelis-Arbuzov rearrangement) With this methodology, tetrafluoro-pyndine phosphonates and phosphmates can be obtained [75, 74], Chlorine fluoride... 

Difluoro-l -vinylcyclopropane undergoes a free radical 1,3 rearrangement with ring expansion yielding difluorocyclopentene derivatives [131 132] (equation 29) Similar, but more complex rearrangement occurs with l,l-difluoro-4-meth ylenespiro[3 2]hexane (equation 30)... 

Carbonylation ot 1-adamantyl triflate in the presence of tnflic acid also gives a derivative of homoadamantane as the result of a similar rearrangement with ring expansion [55] (equation 36)... 

A similar sequence of reactions takes place with the enamlnes of cyclic ketones (55-57) the initially formed unstable cyclobutene rearranges with insertion of two carbon atoms into the ring. A wide variety of cyclic ketones have been allowed to react in this way. For instance, the enamine (75) gave 76 on reaction with dimethyl acetylenedicarboxylate in refluxing toluene (55) and the heterocyclic enamine (77) obtained from dihydro-3-(2H)-... 

Methyl-1,2-dihydropapaverine (175, R = OMe) rearranges to the 2-methyl-3-(3,4-dimethoxybenzyl)-6,7-dimethoxy-3,4-dihydroisoquinolin-ium salt (176, R = OMe) under very mild conditions (treatment with 2% hydrochloric acid). A similar rearrangement of l-(3,4-methyl-enedioxybenzyl) - 2 - methyl - 6,7 - dimethoxyisoquinoline (175, R, R = —O—CHj—O—) affords 3-(3,4-methylenedioxybenzyl)-2-methyl-6,7-di-methoxy-3,4-dihydroisoquinolinium chloride (176, R, R = O—CHj—O—) (256). The reaction was shown to be an allylic rearrangement with internal return (275,275). 

The complementary ABO ester (2,7,8-trioxabicyclo[3.2.1]octyl ester) is prepared from the epoxy ester by rearrangement with Cp2ZrCl2/AgC104. The OBO ester is more easily cleaved by Brpnsted acids than is the ABO ester, but the ABO ester is cleaved more easily by Lewis acids, thus forming an orthogonal set. The ABO ester can be cleaved with PPTS (MeOH, H2O, 22°, 2 h LiOH) the OBO ester is cleaved at 0° in 2 min. ... 

Wittig rearrangement with participation of 0-heterocycles 97LA1275. 

The mechanism proposed by Emmons thus corresponds in part to the decomposition of the trialkyl-oxaziranes by ferrous salts. By radical attack on the 7V-alkyl group of the oxazirane, the radical 32 is formed which rearranges with ring opening to 33. Radical 33 propagates the chain by attack on a further molecule of oxazirane. It takes up an H-atom and is decomposed to ketone and ammonia. The aldehyde produced from the M-alkyl group is converted to tar. 

The rearrangement with ring contraction probably is the most important synthetic application of the Favorskii reaction it is for example used in the synthesis of steroids. Yields can vary from good to moderate. As solvents diethyl ether or alcohols are often used. With acyclic a-halo ketones bearing voluminous substituents in a -position, yields can be low a tcrt-butyl substituent will prevent the rearrangement. 

The initial series of major tranquilizers consists of alkylated derivatives of 4-aryl-4-hydroxypiperidines. Construction of this ring system is accomplished by a set of rather unusual reactions. Condensation of methylstyrenes with formaldehyde and ammonium chloride afford the corresponding hexahydro-1,3-oxazines (119). Heating these oxazines in the presence of acid leads to rearrangement with loss of water to the tetrahydropyridines. Scheme 1 shows a possible reaction pathway for these transformations. Addition of hydrogen bromide affords the expected 4-bromo compound (121). This last is easily displaced by water to lead to the desired alcohol (122) The side chain (123) is obtained by Friedel-Crafts acylation of p-fluorobenzene with 4-chloro-butyryl chloride. Alkylation of the appropriate arylpiperidinol with 123 affords the desired butyrophenone derivative. Thus,... 

Claisen rearrangements with 74 -, Diels-Alder reactions with 74 -, enantioselective reactions 74... 

When heated, the benzotrithiadiazepines undergo a rearrangement with loss of nitrogen to give 1,2,3-benzotrithioles, e.g. the reaction of 6,9-dimethyl-7,8-diphenyl-1,3A4,5,2,4-benzotri-thiadiazepine.393... 

Hydroxyalkyl)porphyrins,84-85 I07b 109 easily accessible from porphyrins by Friedel-Crafts acylation and subsequent reduction, undergo a stereoselective Claisen rearrangement with N,N-dimethylacetamide dimethyl acetal. The substitution pattern and the stereochemical arrangement of the derived chlorins match those of naturally occurring chlorins9 (see Section 1.2.1.2.). 

---