Regioselective Aryne Annulations of N-Tosyl-2-enamides and N-tert-Butylsulfinyl-2-enamides for the Construction of Dihydroquinolin-4-one and Chroman-4-imine Units

A regioselective synthesis of the dihydroquinolin-4-one 4 is achieved from the aryne-mediated annulation of an o -(trimethylsilyl)aryl triflate 1 with N -tosyl-2-enamide 2 in the presence of TBAT in toluene, whereas the chroman-4-imine 5 is formed from the reaction of 1 with N -( tert -butylsulfinyl)-2-enamide 3 and TBAF in THF. Governing factors for regioselectivity have been accounted for as strong steric and electronic effects between N -toluenesulfonyl and N - tert -butylsulfinyl groups in 2 and 3 . The methods described herein are successful with various substrates 1 with 2 or 3 in high levels of regioselectivity, and diastereoselectivity for 5 .