Unexpected rearrangement

When dihydromyrcene is treated with formic acid at higher temperatures (50°C) than that required to produce dihydromyrcenol and its formate, an unexpected rearrangement occurs to produce a,3,3-trimethylcyclohexane methanol and its formate (106). The product is formed by cyclization of dihydromyrcene to the cycloheptyl carbonium ion, which rearranges to give the more stable cyclohexyl compound (107). The formate ester, a,3,3-trimethylcyclohexane methanol formate [25225-08-5] (57) is a commercially avaUable product known as Aphermate. 

These observations can be extrapolated to the pyrrole series the 2-amino derivatives are very unstable whereas 3-aminopyrroles appear to be more stable. 3-Amino-l-tritylpyr-role (162) appears to exist in solution exclusively in the imino-A -pyrroline form (163) (83JCS(P1)93). 2-Aminoindole (164) is unusual in that it exists mainly as the 3//-tautomer (165). 4-Alkylaminoindoles (166) undergo an unexpected rearrangement to 4-amino-1-alkylindoles (167) when heated with p-toluenesulfonic acid hydrate (82CC1356). 

These examples serve to illustrate the fact that, in reactions in which carbenium ions are formed in proximity to the acetal lone pairs, unexpected rearrangements may occur. 

Irradiation (X > 300 nm) of a toluene solution of disilacyclobutane 38 with Ceo afforded the fullerene derivative 39 in a 61% yield, resulting from an unexpected rearrangement of the disilacyclobutane unit [41]. Also this reaction mechanism is still unknown. 

The pathway via the lithio quadricyclane intermediate failed due to an unexpected rearrangement presented in Fig. 2.16. 

An unexpected rearrangement of a 1,3-bishomocubyl ring system [262] accompanies an attempted nitration. The oxidative conditions are requisite for the transformation of a 1,3-dinitro substitution pattern to one with a disjoint polarity sequence (contra-polarization involved). The unusual contrathermodynamic reaction is allowed to occur because of the special steric confinement of the functionalized carbon atoms. The initial fragmentation and Michael addition are also set up by the proper disposition of the nitro groups. 

The reaction of the 2-pyridylvinyl ketone 28 with DMAD could take place in several ways, but nucleophilic attack from the nitrogen and Michael-type addition to the conjugated system gives the indolizine 30.251 A similar cyclization occurs with the diethyl malonate derivative 29 yielding 31, but in the case of 32 an unexpected rearrangement... 

An unexpected rearrangement of dihydro-1,4-thiazine has been reported.109... 

The photochemical reaction of bis(alkylidene)disilacyclobutane (24a and 24b) with C60 by a high-pressure mercury lamp (cutoff <300 nm) proceeds to afford the adducts 26a (61%) and 26b (52%) instead of 2521. The formation of these products is a result of an unexpected rearrangement of the disilacyclobutane moiety (equation 9). The FAB mass spectrum of 26a exhibits one peak at m/z 1056-1059 (CsoFUoSia, M++l cluster), as well as one for Q,o at m/z 720-723. 

Another unexpected rearrangement was encountered in the synthesis of 1 - e/u -valiolamine, when the alkene 4 was subjected to dihydroxylation conditions. Thus, heating of a mixture of 4 with a catalytic amount of OSO4 in a water/pyridine/t-butanol mixture containing trimethylamine N-oxide under reflux for 2 days gave a mixture of 5 (29%) and the a-diol 6 (14%) together with 46% of unchanged alkene 4. 

An unexpected rearrangement was observed during studies directed towards the synthesis of bicyclic keto silanes by the thermal rearrangement of cycloalkanones bearing an co-silylacetylenic chain P to the carbonyl group. Thus, the bicyclic enol silyl ether 2 was formed in 60-65% yield when the ketone 1 was heated neat at 300°C for 2 hours. 

A special experiment showed that the unsymmetrical pentathiepin 41 can be converted into the symmetrical pentathiepin 44 by S2CI2-DABGO in good yield (52%, DABCO= 1,4-diazabicyclo [2.2.2]octane) this is a new and unexpected rearrangement of a 2,3- to a 3,4-fused pentathiepin accompanied by ring chlorination (Scheme 6) <2005OBC3496>. 

Analogous high-yield cyclizations were reported with l-amino-2-nitro-derivatives of pyridines and isoquinolines, which gave the corresponding furoxans [53,54], Anilines oxidized in the presence of indoles afforded Schiff s bases from 2- and/or 3-position in low yield [55], An unexpected rearrangement occurred on treatment of l-phenyl-4-methyl-5-aminopyrimidinone with DIB and catalytic amounts of nickel dichloride, resulting in the formation of an imidazole derivative [56] ... 

Another unexpected rearrangement was observed from 3-phenyliodonio-l,4-naphthoquinone-3-imide which upon treatment with sodium alkoxides was transformed to (2-carbalkoxybenzoyl)acetonitriles [67]. 

A routine addition of HBr across the double bond of a vinylcyclopentane gave a small amount of an unexpected rearranged product. Propose a mechanism for the formation of this product, and explain why the rearrangement occurs. 

The reaction of the stable germylene 32 with a triarylmethylium ion gave not the expected germylium ion 33, but in a series of unexpected rearrangements, the germy-lium ion 34, which is intramolecularly stabilized by interaction of the electron-deficient germylium center with a remote aryl group (Scheme 16).80... 

In the context of a completely different type of chemistry, an unexpected rearrangement occurred upon reaction of C60 with l-methoxy-l-[2-(trimethylsilyl)ethoxy]carbene and afforded a mixture of 1,4-adduct ( )-146 (Figure 1.35) and the corresponding 1,2-adduct instead of the anticipated methanofullerene.299 A crucial role in this reaction course was ascribed by Wudl, Warkentin, and co-workers to the nucleophilicity of the dialkoxycar-bene, the electrophilicity of the fullerene and the (3-stabilization of a positive charge by the trimethylsilyl group. 

An interesting and novel rearrangement of quinoline N-oxides was recently discovered. In synthesizing 2-heptyl-l-hydroxy-4(l//)-quinolone, Hammerschmidt et al. observed an unexpected rearrangement of 4-(alkoxycarbonyloxy)quinoline A+oxidcs 116 to 1-(alkoxycarbonyloxy)-2-heptyl-4(l//)-quinolones 117 <07S1517>. 

In 1971, Yamada et al. published their preliminary smdies toward dendrobine (82) 173). Their starting material was the cheap, commercially available arene thymol, and the key step was an intramolecular Robinson annulation also known as Johnson s tandem reaction. After unexpected rearrangements within an ozoifization, their protocol was modified and in 1972 Yamada et al. were able to present the first S3mthesis of ( )-dendrobine (82) 146). 

Perhaps the most important feature in the modern development of the Smiles rearrangement is its application to heterocyclic chemistry. Various heterocyclic compounds have been approached both with the intended or with unexpected rearrangements. 

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