Reactions circumambulatory

A quantum-chemical study has been undertaken on the isomerization of ctx-1-vinyl-, -1-formyl-, -1-thioformyl-, and -l-iminomethyl-2-vinylcyclopropane to cyclohepta-1,4-diene, 2,5-dihydrooxepine, 2,5-dihydrothiepine, and 2,5-dihydroaze-pine, respectively. Reaction pathways for circumambulatory rearrangements of main group migrants (NO, PO, NCS, SCN, NCO, OCN, SR, Cl, Br, and XX where X... 

Typical examples of circumambulatory rearrangements of bicyclo[3.1. Ojhexenyl cations are shown in Schemes 19 and 20. Swatton and Hart reported the isomerization shown in Scheme 19 in 1967 and proposed that the observed deuterium scrambling could be accounted for on the basis of a cyclopropyl walk reaction153. This circumambulation is comparable to that proposed by Zimmerman and Schuster as part of the sequence of reactions involved in the type A photorearrangement of 2,5-cyclohexadienones. ... 

The ions (216) can be prepared by protonation of the corresponding 2,3-homotropones in fluorosulphonicacid. Irradiation (A > 360 nm, — 70°C)ofthe ions leads to their isomerization. The selectivity shown in the photoisomerizations is attributed to the circumambulatory migration of the C-8 group via intermediates such as (217—219). Photoisomerization about the C-1—O and about the C-2—C-3 bond of the allyl cations (220—222) has been reported cf. the earlier preliminary report. Childs has reviewed the photochemical reactions of protonated unsaturated compounds. 

Another possible reaction, namely circumambulatory 1,3-shifts of the C5 carbon in BCP have not been observed except with carbomethoxy and cyano substitution. 

Benzene oxides also undergo circumambulatory 1,5-oxygen shifts. Finally, the conversion of benzene oxide to phenol was proposed and subsequently found to proceed via an acid-catalyzed reaction part of which involves an intermediate diol. " ... 

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