Spirocyclic oxindoles, alkylative

A similar reaction was reported by Bencivenni, Bartoli, and co-workers [21] about the nitrocyclopropanation of oxindoles. They reported the reaction between methyleneindoline and 1-bromonitromethane catalyzed by bifunctional Brpnsted base/Lewis acid catalyst VIII. The reaction requires one base equivalent for the final cyclization. Mechanistically, the nitromethane addition to methyleneindoline takes place first, and a subsequent intramolecular alkylation renders the final spirocyclic nitrocyclopropane with good yields and excellent diastereo- and enantioselectivities (Scheme 10.10). 

Taking the advantage of the reactivity of alkylideneindolones, Bencivenni and Bartoli developed the nitrocyclopropanation of oxindoles (Scheme 10.15) [21]. The reaction of 1-bromonitromethane (47) with 17c was catalyzed by the bifunctional Bronsted acid-Lewis base cinchona derivative IX. The reaction required 1 equiv of Na2C03 to trap the bromhydric acid released during the last cyclization step. The reaction started with Michael addition of the nitromethane, which was followed by intramolecular alkylation to afford the spirocyclic nitropropanes 48. 

Related Michael-initiated sequential spirocyclizations involving nitrostyrenes as Michael acceptors and functionalized oxindoles as pronucleophiles have been proposed by Lu and coworkers [36]. Alternatively, ( )-p-bromo-p-nitrostyrenes (68) were obtained via a Michael/a-alkylation domino reaction [37]. The reaction was simply catalyzed by the bifunctional Brpnsted Acid-Lewis base catalyst XVII, rendering the final spirocyclopropanes 69 in good yields and excellent stereoselectivities, after epimerization with base (Scheme 10.23). 

---