Construction of dihydropyrano[2,3‐c]pyrazolone via photoinduced Wolff rearrangement/chiral isothiourea catalyzed [4+2] cyclization reaction

Abstract A photoinduced Wolff rearrangement/chiral isothiourea catalyzed [4+2] cycloaddition reaction of pyrazolone derivatives and α ‐diazoketones was developed, affording the corresponding dihydropyrano[2,3‐ c ]pyrazolone derivatives in moderate to good yields (50–94 %) with satisfactory to excellent diastereoselectivities (>20 : 1 dr, in almost all cases) and enantioselectivities of 31–99 %. This protocol features readily available substrates, mild reaction conditions, and effective construction of vicinal tertiary and quaternary carbon stereocenters.