Pd-Catalyzed Tandem Homocoupling-Aldol-Dehydration Of Ortho-Acylphenyl Iodides

Catalytic cascade reaction belongs to one of most efficient methods to constructcomplex polycyclic compounds. Transition-metal catalyzed homocoupling of arylhalides which is employed as a powerful tool to construct aryl carbon (sp2) arylcarbon (sp2) bonds, provides a variety of possible approach for the synthesis ofheterocyclic compounds. Up to now, much significant progress on various transition-metal catalyzed homocoupling of aryl halides has already been achieved, but therehave been rare reports about the transition-metal catalyzed cascade Ullmann couplingreaction of aryl halides, which possibly provides a concise approach to constructcomplex organic compounds. Herein we described a Pd-catalyzed tandem Ullmannhomocoupling/aldol/dehydration of ortho-acylphenyl iodides in which PdCl2(0.05equiv)/DPPP(0.1equiv)/K2CO3(1.5equiv) catalytical system could rapidlyconstruct dibenzo-seven-memebered-ring core in moderate to excellent yield under150℃. All of these compounds were comfired by1HNMR、13C NMR、HR-MS andX-Ray Diffraction. Moreover, the substrate tolerance of this reaction is good, manysensitive functional groups including NH2and halogen could allow for thistransformation. The substituting groups in the benzene ring of ortho-acylphenyliodides possess significantly electronic effects. The electron donating group on thephenyl ring afforded the dibenzo-7-membered-ring compounds in moderate toexcellent yields, and the electron withdrawing group such as5-Cl and5-CO2Et on thephenyl ring gave the desired product in poorer yields. Moreover, no cascadehomocoupling/cyclization product from the electon-poor5-nitro-substitutedphenylketone was observed. Because the dibenzo-seven-memebered-ring core widelyexist in colchicine derivatives，the reaction provides an efficient and convenient routefor the synthesis of colchicine derivatives.Finally, to further investigate the reaction mechanism, some related controlreactions were conducted in order to trap some possible byproducts and intermediates.On the basis of the controlled experiments, we proposed possible reaction mechanismwhich involved homocoupling/Aldol condensation/dehydration.