Ring exchange

C5D5 —MCI2 (260). Although this indicates that ring exchanges in Cp M is fast, other studies have shown that the ratio of exchange products depends... 

A more highly substituted pyrrolidone, doxapram, shows activity as a respiratory stimulant. Preparation of this agent involves an interesting rearrangement, which in effect results in a ring exchange reaction. Alkylation of the anion from diphenylacetonitrile with the chloropyrrolidine 14 affords 15. Hydrolysis of the nitrile function leads to the... 

The furan transfer reaction was extended to the furan-pyrrole ring exchange reaction by using propargylamines [138],... 

For the biochemically interesting purines formed by fusion of a pyrimidine and imidazole ring, exchange can take place either at the C-2 or C-8 positions. Preliminary results in the case of adenine (52)... 

The first study of ring-exchange reactions involving metallocenes has shown that vanadocene is quite inert to exchange with both Li(C5D5) and Ni(jt- 503)2. ... 

Interesting new developments in chromium chemistry which have been reported this year include the preparation of butadienetetracarbonylchromiurn by treating chromium atoms with butadiene, followed by subsequent treatment with The first ring-exchange reactions involving metallocenes have... 

In general, self-activation of all picolines with platinum oxide yields a predominance of isotope incorporation in the methyl side chain. This orientation has been attributed to a site effect in that catalytic sites formed by alkyl group reduction of platinum oxide favor side-chain deuteration at the expense of ring exchange. 

Decamethylferrocene, [FeCpf] (Cp = // -CjMes) [26], is the most common alkylated ferrocene derivative used for the preparation of CT complexes. [FeCpf] and its oxidized form, as is the case for most other decamethylmetallocenes [27], has Djj symmetry in the solid state. For use as an electron-donor it has the important advantage that it is resistant towards substitution reactions, ring exchange, and hydrolysis. It is also much more electron-rich than its parent compound, as reflected by the redox data reported in Table 8-1. 

This conclusion is also supported by evidence for another complex in the series 3a. The H spectra (Fig. 1) as well as the C NMR spectra show that simultaneously with the first (low barrier) process exchanging A -methyl groups also the C-methyl groups, which reside each on a different chelate ring, exchange and coalesce. It is thus evident that this first process effects an exchange of the chelate rings. 

FIGURE 16.21 Six-mem-bered rings exchanged for seven-membered rings. 

The complex [Mn(fj-C5Me5)2] is oxidized to the monocation (E° = -0.56 V) and reduced to [Mnfo-C5Me5)2] (E° = -2.50 V in MeCN), which is isolable as a pyrophoric sodium salt using sodium naphthalide in thf. The anion is isoelectronic with ferrocene but does not add electrophiles to the rings and is stable to ring exchange. Needless to say, it is an extremely powerful one-electron reductant (442). 

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