General Method for the Construction of ortho-tert-Butyl Phenols & 3,4-Dihydro-2H-1,3-benzoxazines via Base-Promoted ortho-Quinone Methide Chemistry; A Review of Generation of aza-ortho-Quinone Methide and Its Applications
Ortho-quinone methides (o-QMs) are highly reactive electrophiles, which have been well used in chemical synthesis. Our group developed a base-promoted method to generate o-QMs in-situ, which is subsequently used for [4+2] cycloadditions with a dienophile and 1,4-conjugated additions with a nucleophile. In this thesis, I would like to discuss two new methods for synthesizing privilege structures using our base-promoted o-QM chemistry. In the first part of this thesis, a new general process for construction of a variety of ortho-tert-butyl phenols via o-QMs is presented. In addition, other known methods for construction of ortho-tert-butyl phenols were also evaluated regarding to their regioselectivity, efficiency and functional group tolerance. By comparison, we concluded that our o-QM chemistry provides better yields and also tolerate an assortment of functional groups for delivering ortho-tert-butyl phenols. In the second part of this thesis, a one-pot method for combining three separate components leading to a variety of N-substituted 3,4-dihydro¬-2H-1,3-benzoxazines is described. This method involves the addition of a Grignard reagent to an ortho-OBoc salicylaldehyde derivative in the presence of an imine. With an assortment of imines tested, 15 examples of N-substituted 3,4-dihydro-2H-1,3-benzoxazines are presented, including the diastereoselective incorporation of racemic imines. In the third part of this thesis, I would like to discuss about aza-ortho-quinone methides (aza-o-QMs), an analogue of o-QMs. Aza-o-QMs are very similar to o-QMs for their highly electrophilicity. Nevertheless, aza-o-QMs are far less explored comparing to o-QMs. Therefore, I would like to use my experience in o-QMs to propose a more general method for base-promoted aza-o-QMs generation and its future applications suitable for our group.