Lewis Acid Catalyzed Or Promoted Tandem Reaction Of Enynes And Propargyl Alcohols

This thesis mainly focuses on the cascade reaction of alkynes and propargyl alcohols under Lewis acid, which were divided into two parts.Part Ⅰ:Gold-catalyzed tandem reaction of enynesOver the past few decades, gold complexes or salt as a catalyst has played an important role in organic chemistry, especially in the area of enynes, which is mainly based on the structure character of gold. Gold is later transition metal located in the sixth period. Moreover, the outermost electron configuration of gold element is [5d106s1]. Therefore, gold, in its high state, the central metal ion has an empty orbit (d - orbit), which can coordinate with rich electron groups or compounds. Furthermore, gold not only act as transition metals but also as lewis acids. In this respect, numerous efforts have been made. The π-acid of gold shows high affinity for polarizing alkyne bonds, even in the presence of other rich electron receptors. After coordinating to gold, alkyne is polarized to active intermediates with duble cationic-carbenoid character, which reacts with various nucleophiles to complete the depolarization, thus forming a series of useful and complex compounds. In recent years, based on this point, we have explored the gold-catalyzed tandem reaction of enynes with oxygen-containing groups as nucleophilic reagent, which could to selective synthesis of the four different polycyclic skeleton compounds.1, We have developed an efficient gold-catalyzed cascade reaction for the construction of oxanorbornenes and naphthalene derivatives from easily prepared hydroxy enynes. The sequences involve a highly regioselective 5-exo-dig cycloisomerisation, followed by a Diels-Alder reaction to afford oxanorbornenes. With the same hydroxy enynes, we also obtained naphthalene derivatives using a different catalytic system by further aromatization reaction. Based on the controll experiments, we found that gold catalysts are effective to catalyze all three processes in this tandem reaction. The value of this cascade reaction is reflected by the applicability of diverse alcohol substrates and good compatibility with functional groups.2, After achieving the gold-catalyzed cascade cyclization of the hydroxy enynes, we found that the treatment of the enynones with a gold catalyst would give interesting oxabicyclic compounds or naphthyl ketones, Initially, the coordination of the alkynylmoiety of enynones with gold catalyst gives stable gold-carbonyl ylides or benzopyrillium intermediates, and subsequently undergo intramolecular [3+2] or [4+2] cycloaddition with dipolarophiles to construct two kinds of functionalized polycyclic compounds.Part Ⅱ:Lewis acid mediated tandem reaction of propargyl alcohols.In recent years, the transformation of propargyl alcohols becomes a fundamental method due to its special bifunctional character, which has attracted increasing attention in modern organic synthesis. With the help of Lewis acid and Br(?)nsted acid, an allenyl cation could be generated via tautomerization of the propargyl cation and then be attacked by nucleophiles, leading to the different sorts of reactions. So far, various nucleophiles have been developed to capture the allenyl cation to form different compounds. These nucleophiles include: a) Electron-Rich Arene; b) Enols or Enamines; c) Alkenes; d) Heteroatom Nucleophiles; e) Halide. On the basis of the character of propargyl alcohols in the presence of Lewis acid, our group has also systematically studied the Lewis acid-mediated tandem reaction of propargyl alcohol, which could to selective synthesis of the four different containing-nitrogen compounds.1, A novel and direct synthesis of 1-aryl-5-arylvinyl-tetrazoles from easily prepared propargylic alcohols and TMSN3 has been developed in the presence of TMSC1. The process may involve multiple intermediates, such as allenyl cation, allenylazide and carbon-nitrogen three bond. With the optimized conditions in hand, we explored the scope of propargylic alcohols. We found that this reaction tolerates a variety of propargylic alcohol substrates under mild conditions and can be scaled-up to grams. Furthermore, on the basis of control experiments, these results clearly indicate that allenylazide is involved in this novel transformation.2, Further studies on the intermediate allenylazide, we found that the proposed mechanism involves the Schimidt-type rearrangement of allenylazide intermediate to form intermediate I (-CN+). In order to verify the reaction intermediate I, by controlling the amount of azide and water, we found that the intermediate I could be trapped by water to form a series of a,β-unsaturated amides. Moreover, in this rearrangement process, the results with high chemoselectivity indicate that aryl groups have a greater migratory aptitude to the nitrogen atom than alkenyl groups.3, we have developed a novel BF3·Et2O promoted tandem transformation of propargylic alcohols into the corresponding 2-alkenylated benzoxazoles and benzimidazoles. Moreover, such processes could be performed under mild conditions and in a short time, giving the target compounds in good yields and broad substrate scope. Notably, this protocol offers a new synthetic strategy for the synthesis of biologically and pharmaceutically important benzoxazoles and benzimidazoles.