Five-membered heterocycles are good nucleophiles

The reactivity of these five-membered systems with nucleophiles has received note. Zatsepina and Tupitsin and their co-workers recorded the use of deuterium exchange rates in methyl groups of five-membered heterocycles in ethanolic KOEt as a source of o values, with a p value of 4.7.271 Spinelli and his co-workers revealed that even for tri- and tetrasubstituted five-membered heterocycles the Hammett equation employing er values where appropriate gives good correlations. The systems studied are 32-37, in all cases the slow step... 

Hassner and coworkers have developed a one-pot tandem consecutive 1,4-addition intramolecular cycloaddition strategy for the construction of five- and six-membered heterocycles and carbocycles. Because nitroalkenes are good Michael acceptors for carbon, sulfur, oxygen, and nitrogen nucleophiles (see Section 4.1 on the Michael reaction), subsequent intramolecular silyl nitronate cycloaddition (ISOC) or intramolecular nitrile oxide cycloaddition (INOC) provides one-pot synthesis of fused isoxazolines (Scheme 8.26). The ISOC route is generally better than INOC route regarding stereoselectivity and generality. 

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