Five-membered cyclic nitronates additions

Finally, Scheme 3.14 presents the Michael addition of bromomalonic ester to conjugated nitro olefins 10. This approach allows one to synthesize five-membered cyclic nitronates (5) doubly functionalized at the C-5 atom (Scheme 3.14, Eq. 5). 

Cycloaddition of Nitrocarbenes. Scheme 3.24 presents possible approaches to the synthesis of five-membered cyclic nitronates (24), where [3 + 2]-cyclo-addition of intermediate nitrocarbenes (as dipoles B) to olefins as trapping agents is the key step. 

It should be noted that tetramethylethylene was involved in the [3+ 2]-cyclo-addition with five-membered cyclic nitronates (363). 

The mechanism of this reaction has not been studied in detail. However, it can be represented as a sequence of reactions. The first reaction is, in fact, [3+ 2]-cycloaddition of olefin to furoxan (161). Under severe conditions, the resulting intermediate A undergoes fragmentation to give five-membered cyclic nitronate B. The latter is involved in the usual addition reaction with an excess of olefin to form isolable bicyclic product (162) (301, 378, 379). 

In addition, chiral five-membered cyclic nitronates can be prepared from optically inactive starting nitronates with the use of ligated palladium (catalyst) as a chiral inductor (71) (ee 97%). 

In the case of five-membered, cyclic nitronates, the NMR resonances for C(3) appears in the same region as C(a) in the silyl nitronates (Table 2.20) (60,62,74). In addition, C(5) is observed between 72 and 92 ppm. For six-membered cyclic... 

The Chmielewski group has pubHshed extensive studies on the addition of cycHc nitrones to a,P-unsaturated 8- and yl ctones. While five-membered ring nitrones (e.g., 229) react with 8-lactones (e.g., 230) exclusively via an exo-approach because of unfavorable steric interactions, they react with y-lactones (231) through both endo- and exo-transition states, giving rise to mixtures (Scheme 45) (2006TA68). Lactones bearing substituent groups react in such a way that the nitrone approaches the Tt-bond from the face of the alkene opposite the substituent. Cyclic nitrones can adopt conformations that clearly define the location of a substituent on the dipole. For example, reaction 232 with 231 produced only two... 

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