Applications Of Modified Allylic Compounds In Synthesis Of Bisphosphine Monoxides And Stereoselective Three-component Olefination Reaction

Recently, a class of modified allylic compounds, derived from the Morita-Baylis-Hillman adducts, such as allylic halides, allylic acetates, allylic carbonates etc, have attracted much attention from synthetic chemists. Under the catalysis of Lewis bases, these allylic compounds readily undergo allylic alkylations with a series of nucleophiles; under the catalysis of tertiary phosphines, various cycloadditions can be successfully achieved with electrophiles. In this thesis, the following two kinds of new applications of allylic carbonates in organic synthesis have been explored:First, starting from allylic carbonates, a new synthetic approach for a novel type of bisphosphine monoxides was successfully devised.Bisphosphine monoxides, as a class of phosphorus ligands, have broad utilities in the catalysis and pharmaceuticals. Their synthetic methods can be classified into two categories:one is via characteristic coupling of two monophosphines with different oxidation states; another is by the selective mono oxidation of bisphosphines. Those known methods all have their own limits and drawbacks. In this work, a new process based on allylic carbonates has been developed:under the catalysis of a Lewis base, the allylic carbonate reacts with diphenylphosphinate or diethyl phosphonate, forming monophosphine oxide bearing an activated alkene moiety; subsequent hydrophosphination of the prepared monophosphine oxide with HPPh2 under the influence of a base readily affords the bisphosphine monoxide. The structures of the obtained bisphosphine monoxides have been confirmed by 31P NMR, 1H NMR,13C NMR spectroscopy.Secondly, for the first time, a three-component olefination reaction between allylic carbonate, phosphine and aldehyde has been realized.Phosphine-catalyzed annulation reactions of allylic carbonates with activated olefins or imines have been attracted much research interest from organic synthetic chemists. In these reported reactions, it is generally considered that an in situ formed phosphorus ylide is the key intermediate. On the basis of this concept, a three-component olefination between allylic carbonates, phosphines and aldeyhdes has been achieved for the first time. Results from this study show this reaction has a broad substrate scope, providing a general method for highly stereoselective synthesis of trisubstituted 1,3-dienes. The structures of the olefination products have been determined by 1D and 2D NMR spectroscopy and X-ray diffraction. Through 31P NMR monitoring experiment, the in situ formed phosphorus ylide intermediate was observed, which was also confirmed by comparison with directly prepared allyl phosphorus ylide. Also, the high stereoselectivity of the Wittig olefination has been well rationalized.