(Ⅰ) Pd(0)-catalyzed Dearomatization Of Furan Rings (Ⅱ) Selective Reduction Based On Insitu-generated π-allylnickel

Dearomatization of aromatic compounds has attracted considerable attention because itprovides a simple method to achieve functionalized alicyclic synthetic building blocks whichcan be utilized as intermediates for the preparation of natural products and bioactivecompounds. Of particular interest is the dearomatization of furans due to their low Dewarresonance energy of4.3kcal mol and because furan rings contain masked functionalities ofolefin, diene, enol ether, and1,4-dicarbony. Accordingly, their partial dearomatization allowsthe reactivity of the remaining unsaturation to be intensively exploited. To date, there are anumber of different methods that, with unequal scope, allow the dearomatization of the furanring and which have been used extensively in the synthesis of numerous bioactive molecules.Among these methods, there are only a few examples of transition-metal-catalyzeddearomatizing processes being used for organic synthesis. We successfully achieve thedearomatization of furan rings through the series process, which is the Pd-catalyzed furanintramolecular α-aromatizing/furan ring-opening/β-H elimination. While we take advantageof this method to synthesis a series of3-substisuted benzofurans and3-substituted indoles.The combination of NaBH4with a catalytic amount of NiCl₂, which generates a highlyreactive nickel boride species in situ, has been extensively employed to reduce functionalgroups that are inert to sodium borohydride alone. This system is especially attractive for itslow cost, simple manipulations, short reaction times （generally requiring only a few minutes）.Therefore, expanding the application of this reducing system in organic synthesis is of greatpractical significance. However, to the best of our knowledge, little attention has been paid tothe regioselectivity and stereoselectivity of these reductive reactions involving the NaBH₄–NiCl₂system. The regioslective reduction of alactron-rich dienes and the reductive cleavageof allyl esters are fulfilled by this catalytic system, both of the reductive reactions mayinvolve Ï€-allylnickel intermediates generated from fresh nickel boride.