Cyclophanes bromination

During the synthesis of [2.2]paracyclophanediene, Dewhirst and Cram 83> prepared the bis-geminal dibromides 4a and 4b, which were subsequently converted into the diketones 5 a and 5 b. The UV spectra of the bromides 4a and 4 b show maxima at 236 nm. A comparison with the Amax values of other [2.2]paracyclophanes brominated at the bridges suggests that the absorption at 236 nm is the 235 nm band of [2.2]para-cyclophane, shifted bathochromically by the inductive effect of the... 

Rezaie and Bremner reported the synthesis of tricyclic 1,4-thiazepines by ring contraction. OT-Cyclophane lactam 237 was treated with Ar-bromosuccinimide and azoisobutyronitrile to yield 47% of dihydroindole derivative 238, as the major product next to side products 239-242 (Scheme 42). The same reaction condition was applied for the ester derivative of 237 (X = COOCH3>, but with longer reaction time. This resulted in indole analogues 240-242 (X = COOCH3) without the formation of dihydroindole derivatives. Bromination on the aromatic ring was observed prior to the intramolecular cyclization. The exact mechanism has not been resolved, but a possible reaction sequence could be... 

Halogen atoms, like any other substituents, modify the symmetry of the framework to which they are attached. Unlike many others, however, they introduce no conformational complications of their own since, in a mechanical sense, they are cylindrically symmetrical (locally CJ about the bond axis. (See, e.g., the discussion of Cram and coworkers17 of the numerous point symmetries potentially available in bromine substituted [2.2]-para-cyclophanes.)... 

An interesting [2.2]paracyclophane-bismuth bromide 1 2 adduct has been investigated. It forms self-organized extended (BiBra) chains, in which each bismuth atom participates in two Bi-Br bridges (with two short bonds Bi-Br 2.676 and 2.663 A, and two secondary Bi- -Br bonds 3.325 and 3.402 A) and is connected to a terminal bromine (Bi-Br 2.595 A). The chains are interconnected by the para-cyclophane molecules, each one connected in a fashion to two adjacent chains [460]. 

The precursors of cyclophanes 161, i.e., podands 156 were prepared in four steps starting from 3-ethylquinoxalin-2-one 159 (Mamedov et al. 2(X)5a Kalinin and Mamedov 2009), the alkylation of which with dibromooxoalkanes leads to 160 with ethyl moieties. The transformation of ethyl acetyl fragments was accomplished in three stages bromination, the substitution of the bromine atom by the azide group, and conversion of azidoethyl fragments into acetyl function when heated in aqueous acetic acid. 

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