Researches On Petasis Reaction Of4-Substituted-1,2-Oxaborol-2(5H)-Ols

The Petasis reaction is a highly versatile multicomponent reaction, which can form different types of molecules and also enable the synthesis of a variety of novel structures and heterocycles with a high degree of molecular diversity. This process is widely utilized in combinatorial chemistry and drug discovery.This thesis mainly focused on the researches on Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols and has successfully developed two novel reaction protocols:(1) One-pot synthesis of functionalized2,5-dihydrofurans via an amine-promoted Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols.(2) Regioselective synthesis of dihydropyrone derivatives via Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols. The mechanisms of two reactions were explored separately.Amine-promoted Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols with salicylaldehydes, provides a one-pot and efficient route toward functionalized2,5-dihydrofurans. The process, which combines alkenyl boronic acid-based Mannich reaction and a highly efficient intramolecular SN2cyclization, provides a novel method to construct the substituted2,5-dihydrofurans from simple starting materials.Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols, glyoxylic acid and amines, which provides a one-pot route to prepare3-amino-3,6-dihydro-2H-pyran-2-ones and3-amino-5,6-dihydro-2H-pyran-2-ones with high selectivity under different conditions. The reaction process combines a alkenyl boronic acid-based Mannich reaction and a highly efficient intramolecular lactonization. The latter also contains rearrangement reaction of carbon-carbon double bond in the presence of amine. The intermediate was isolated, which provides effective evidence toward proposed mechanism, In addition, we also isolated the products of reaction that two equivalents of aldehyde and amine component are involved in and tentatively propose a possible reaction pathyway for this reaction. The method provides a novel strategy to construct dihydropyrone derivatives from simple starting materials through convenient procedures.In summary, we synthesized two types of heterocyclic compounds of dihydrofurans and dihydropyrones via Petasis reaction of4-substituted-1,2-oxaborol-2(5H)-ols, which provides a novel approach to synthesize natural products and bioactive molecules with related structures.