Facile intramolecular rearrangement

H. B. Mereyala and S. Guntha, Stereoselective synthesis of rare (d and l) mono and disaccharides of 5-deoxy hexofuranosiduronic acids by a facile intramolecular rearrangement of hemiacetal heptonolactone alcohols, Tetrahedron, 51 (1995) 1741-1762. 

The zirconium(IV) complex 27, with one and one t -allyl unit, upon heating, undergoes facile intramolecular rearrangement to a 3-allylmetallacyclobutane complex 28, which after treatment with silver(I) triflate releases allylcyclopropane (29) in quantitative yield. ... 

Phosphine substituted complexes also undergo a facile intramolecular rearrangement at low temperatures. Two distinct carbonyl signals are seen in the NMR spectrum, which interconvert even at 0°C via a process believed to involve a capped trigonal-prismatic intermediate (1073). Related phosphine... 

Au9(P(4-MeOC6H4)3)g] +, has a centered crown structure (26). The two compounds have similar electronic spectra and P NMR spectra even at low temperature, indicating that these compounds undergo facile intramolecular skeletal rearrangement in solution. 

Intramolecular photodimerization of 2-pyridones provides a series of primary photoproducts, the structures of which were a function of the chain length comecting the two reactive centers." The initially formed dimers were characterized as being derived from a photochemically allowed [2 + 2] cycloaddition process in each case examined. A particularly interesting example from this study in terms of [4 + 4] cycloaddition chemistry is the conversion of dipyridone (114) into Ae net [4 + 4] dimer (115) via a facile thermal rearrangement. " Further irradiation of the [4 + 4] species (115) produced a second [2 + 2] adduct that was isomeric with the initially formed metastable species. 

The carbenes 1 can be trapped by intermolecular [1 + 2] cycloaddition to cyclopentadiene to give 2,357 and furan to give 3 and 5,356-357 but intramolecular reactions always compete. As expected, the furocyclopropanes undergo facile thermal rearrangement reactions, e.g. 3 —> 4 and 5 -> 6. 

The important application of 4-alkynyl-3-methoxy-4-hydroxycyclo-butenones includes their ability to cleave supercoiled DNA by a mechanism that involves contribution from a diradical intermediate. The 4-alkynyl-4-hydroxycyclobutenones, which bear alkyl group at position 2 can effectively damage DNA, as opposed to the corresponding 2-alkoxy analogs (the latter could rearrange to their epoxides by a facile intramolecular pathway). For... 

Fullerene nitro functional groups were found to be unstable thermally in solution or in SO, which prohibits the direct purification and separation of polynitrated isomers. The instability of these compounds arises from the facile occurrence of the intramolecular rearrangement into corresponding nitrites and further polyhydroxylated by hydrolysis ... 

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