Nitrosation fundamentals

Besides, cyclic nitroso acetals have attracted considerable interest because [3+ 2]-cycloaddition of nitronates to olefins provides a simple and efficient procedure for the synthesis of five-membered cyclic nitrosals (see Scheme 3.153). Hence, knowledge of the configurations of these products allows conclusions about the mechanism of this very important process. However, it is impossible to distinguish kinetic and thermodynamic products of [3+ 2]-cycloaddition of nitronates to olefins without studying such a fundamental problem as the stereodynamics of five-membered cyclic nitroso acetals, that is, the ring and nitrogen inversions. 

Electrophilic nitration and nitrosation of aromatics are fundamental synthetic organic reactions and are well understood in terms of mechanism/ On the other hand, similar nitration and nitrosation of alkanes were only studied in the 1970s and 1980s. 

The nitrosation reactions and the chemistry of diazoalkancs are also used in synthesizing just certain specific types of compounds, like cydopropancs. The mechanisms here are more involved, however, and an understanding of their steps at this point is helpful because similar types of chemistry will be. seen again later, in Chapter 22. As you plow through this, try to focus on the relationship of each mechanistic step to processes you ve seen before. Almost all of this chemistry is based on relatively fundamental sorts of events, like protonation and deprotona-tion, combined with elimination or addition. 

Consequently the change in the acidity profile has been linked to a fundamental change in the rate-determining step. Thus unlike the situation at lower acidities, where the initial A-nitrosation is always rate controlling, the slow step at very high acidities may be proton loss from the intermediate nitrosamine ion (14) as shown in Scheme (16) °. ... 

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