Ring walk

Photochemical scrambling of ring atoms can involve a ring-walk or a cyclopropene mechanism. 

Almost all rj2-arene complexes of [Os] are amenable to both intrafacial (i.e., ring-walk) and interfacial (i.e., face-flip) isomerization mechanisms, which allow the metal to coordinate to the most thermodynamically favorable position (Figure 2). Aromatic molecules bearing a redonor group (e.g., anisole, aniline, phenol) tend to place the metal across C5-C6 in order to... 

Strawser D, Karton A, Zenkina OV, Iron MA, Shimon LJW, Martin JML, van der Boom ME (2005) Platinum stilbazoles ring-walking coupled with aryl-halide bond activation. J Am Chem Soc 127 9322-9323... 

Rhodium tetraacetate, as catalyst, in O-alkylation 666 Rhodococcus 978 Ring current effects 336 Ring inversion, cone-to-cone 1385, 1386 Ring-walk isomerization 283 Ripening, state of, effect on organoleptic properties of foodstuffs 913 River water, analysis of 946, 947, 962, 977 Road particulate matter, phenoUc compounds in 938... 

The cyclic ether (219) was converted into (220), which underwent rearrangement to (221) in a manner analogous to the celebrated norcaradiene ring-walk stereochemical analysis of the rearrangement indicated predominant inversion of configuration for both the photolytic and thermal processes and so symmetry considerations of the Woodward-Hoffman type may not be relevant to these (or at least the thermal) processes.559 Esters of pinocarveol were converted into myrtenyl compounds by CuOAc.560 cis- and rrans-Verbenyl and verbanyl acetates,561 562 related compounds563 and 2-methylverbanone564 have been synthesized for evaluation as attractants for cockroaches. 

Under the topic circumambulatoiy rearrangements R. F. Childs (3) has recently reviewed migrations of mono-, di-, tri- and tetravalent groups around the periphery of a ring. Walk rearrangements of [n.l. 0] bicycles are included as one topic of this more general review. 

Scheme 39. Possible routes for intrafacial migration of arenes. (i) Migration to a c-C-H (ii) C-H oxidative addition (iii) cr-arenium ring-walk (iv) f/ -allyl ring-walk.

The latter possibility for epimerization at C9 is unlikely given observations with a 9-cyano-9-methyl derivative in which C9 undergoes an allowed 1,7 carbon ring walk with inversion of configuration at 100°C (Scheme 10.18). Furthermore, retention of configuration at C9 is at least 10 000 times slower than inversion. 

How far can the catalyst diffuse or ring walk along the polymer backbone before either oxidative addition to a carbon-halogen bond or dissociation of the catalyst ... 

Scheme 7.6 Ring walk mechanism of nickel insertion, via the preferential coordination of Ni(PEt3)4, followed by intramolecular oxidative addition.

Scheme 7.13 Chain growth polymerization of a bithiophene monomer by Ni ring walk across a nonconjugated monomer.

Isomers of 2,9-dimethylbicyclo[6.1.0]nona-2,4,6-triene-9-carbonitrile (1) also undergo interconversion by a symmetry-allowed 1,7-carbon ring walk with inversion of configuration at 100 °C (Scheme 3.37). 

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