[4 + 2] Cycloadditions of 1-Phosphono-1,3-butadienes with Nitroso Heterodienophiles: A Versatile Synthetic Route for Polyfunctionalized Aminophosphonic Derivatives
yl)-1,3-butadiene, and 1-(diethoxyphosphonyl)-3-tert-butyldimethylsilyloxy-1,3-butadiene with various nitroso heterodienophiles has been investigated as a new synthetic route for aminophosphonic derivatives. The HDA cycloadditions regioselectively led to the proximal isomers, i.e., presenting the NR3 group in the meta position regarding the phosphonate substituent. From the resulting 6-phosphono-3