Inserting a radical label at position 9 of bispidine using the Horner—Wadsworth—Emmons reaction to create a spin-labeled organocatalyst

Abstract

A bispidine derivative containing a paramagnetic moiety at position 9 was first synthesized by the Horner—Wadsworth—Emmons reaction between bispidine and a suitable radical-labeled reagent. The structures of diethyl {2-[(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl)amino]-2-oxoethyl}phosphonate, the free radical used as a reagent in this reaction, and 2-(3-benzyl-3,7-diazabicyclo[3.3.1]nonan-9-ylidene)-N-(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl)acetamide, the target radical, were confirmed using a combination of physicochemical analysis methods (mass spectrometry, EPR spectroscopy, and X-ray diffraction). Using the obtained spin-labeled catalyst, the EPR monitoring of the Michael reaction (addition of diethyl malonate to nitrostyrene) was carried out for the first time, which made it possible to formulate principles for designing catalysts with reporter groups.