Friedel–Crafts reaction of electron-rich (het)arenes with nitroalkenes

Diastereoselective 1,6-Addition of α-Phosphonyloxy Enolates to para-Quinone Methides

The addition of α-ketoamide to p-quinone methide initiated by dialkylphosphite in the presence of organic base 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) is explored. Coupling of dialkylphosphites to α-ketoamides in the presence of a base follows [1,2]-phospha-Brook rearrangement, generating corresponding α-phosphonyloxy enolates that are subsequently seized by p-quinone methides (p-QMs). The two-step one-pot 1,6-conjugate addition provides effective access to a series of isatin-incorporated phosphate-bearing 1,6-adducts having two vicinal tertiary carbons with up to 90% yield and >20:1 dr.

Synthesis and practical applications of 2-(2-nitroalkyl)pyrroles

Functionalization of pyrroles introducing a 2-nitroalkyl moiety allows the formation of nitro-containing compounds to be used as pivotal intermediates for the synthesis of bioactive compounds. The reaction of pyrroles with nitroalkenes under the Friedel-Crafts conditions allows a direct entry to 2-(2-nitroalkyl)pyrroles. This approach can also be used for the preparation of enantioenriched derivatives exploiting asymmetric catalysis. In a complementary fashion, the Henry reaction between 2-formylpyrroles and nitroalkanes generates the corresponding nitroaldol products which upon dehydration and reduction of the intermediate 2-pyrrolylnitroethene efficiently afford 2-(2-nitroalkyl)pyrroles. This review article summarizes the most relevant procedures for the preparation of 2-(2-nitroalkyl)pyrroles during the last two decades as well as their significant practical applications.