Exotic reaction

The lists of reactions provided by molecular, supramolecular and semiconductor PCs vide supra) suggest certain perspectives for their practical applications for fine organic synthesis. Note, that sometimes PCs act selectively producing a sole product in rather exotic reactions in other cases, a whole set of exotic products can be produced from the same reagents vide supra). 

Cobalt occurs in vitamin B12. This vitamin is very complex and is required for some exotic reactions of metabolism. A deficiency of vitamin B12 results in pernicious anemia. More about this vitamin follows in chapter 15. 

The second chapter deals with cellulose solutions in yet another solvent system for cellulose, namely DMAc/IiCl, which is not used on an industrial scale as is NMMO, but on the laboratory scale for analytical purposes. The presence of the somewhat exotic reaction medium poses special requirements on trapping methodology that was used to clarify the mechanisms of different degradation processes. This issue was of importance since maintenance of cellulose integrity is the key prerequisite for any analytical procedure which should report the polymer characteristics of the genuine cellulosic material. 

The reaction of 2-methyl-3-thioformylindole 173 with 2-aminoethanethiol led to the formation of the 1,3-dithie-tane 176 in 8% yield, and also two Schiff bases 174 and 175 (Equation 28) <1999RJO1507>. The rather exotic reaction of 4-diethylamino-3-butyn-2-one 177 with l-isothiocyanato-4-nitrobenzene 178 has also been reported <2001SL361>. After 4h of heating in THF of the substrates, the substituted thiete 179 and dithietane 180 were isolated in 46% and 35%, respectively (Equation 29) <2001SL361>. 

Protons and carbenium ions always add to C=C double bonds via carbenium ion intermediates simply because no energetically favorable onium ions are available from an attack by these electrophiles. An onium intermediate formed by the attack of a proton would contain a divalent, positively charged H atom. An onium intermediate produced by the attack of a carbenium ion would be a carbonium ion and would thus contain a pentavalent, positively charged C atom. Species of this type are at best detectable under exotic reaction conditions or in the norbornyl cation (Figure 2.25). 

The exchange of tin for lithium or other metals is probably the most valuable job it does. Reagents such as BuLi attack tin or boron directly rather than removing a proton. Silicon is not usually attacked in this way and proton removal is more common. In the next chapter we shall see how transition metals open up a treasure chest of more exotic reactions for which the reactions in this chapter are a preparation. 

Exotic reactions like the ignition of a H2-CI2 mixture by optical radiation will not be covered in this book. 

The product, which is isolated in 25% yield, contains a V=V with semibridging carbonyl ligandsT Other examples of six-electron donors are more exotic. Reaction of Fe3(CO)i2 with allene leads to a bisallyl complex. ... 

Catalyst Selection. The choice of catalysts determines not only the rate of PUR formation by means of the fundamental reaction between isocyanates and their partner reactants, but also the contribution of some of the more exotic reactions of the isocyanates. The rate of PUR formation is, of course, of critical importance to the reaction-injection molding and reinforced-reac-tion-injection molding technology. Among the exotic reactions of the isocyanates the following may be worthy of note. 

Because of structural variety that allows one to modify the mode of deformation, distorted condensed benzenoid (and non-benzenoid as well) aromatics will continue to be a source of exotic reactions. These molecules will continue to accept challenge of synthetic chemists because new alternative methods should always be developed. Moreover, these investigations of special 71 bond systems will certainly deepen our understanding of chemical bonding, but also would provide opportunities of finding useful reactions and functions of organic molecules. 

This study also revealed the validity of the enthalpy-entropy compensation effect even for such an exotic reaction as the transfer of a CyD complex from H2O to D2O (see Fig. 8.8) ... 

At the cost of a short digression from group 15 chemistty, a brief comment may be warranted on these exotic reactions. The remarkable species CH5+ is best thought of as a complex of CH3+ and H2, with a three-center two-electron bond, reminiscent of B-H-B bonding in diborane. 

NR is essentially a simple olefin and therefore, in theory, amenable to the very many known chemical reactions of such species. The trialkyl-ethylenic double bond is electron rich via inductive and hyper-conjugative effects although somewhat sterically hindered. The better knoi n chemical modification of diene rubbers, including NR, have been reviewed although the literature contains many other examples of more exotic reactions. Most reactions pertinent to a trialkyl ethylene have been tried on NR and, in general, they work with variable degrees of efficiency. However, usually only solution-phase chemistry has been employed. 

Although initially developed as a rather exotic reaction, the intramolecular transace-talization reaction can also be a very useful tool in asymmetric synthesis of important chiral compounds and natural products. Both, starting materials and products of the intramolecular transacetalization reaction are protected y-hydroxycarbonyl compounds, orhomoaldols (Scheme 13). Homoaldols are versatile motifs in organic synthesis that can be easily transformed into a vast array of important chiral compounds. However, due to the problematic homoaldol disconnection, these compounds are not readily available in a catalytic asymmetric fashion. 

---