DAUBOR · Design and Applications of Unconventional Borylation Reactions

Boronic esters are versatile synthetic intermediates for the preparation of a wide range of organic molecules. The recent approval of the anti-cancer agent Velcade, the first boronic acid containing drug commercialized, further confirms the status of boronic acid derivatives as an important class of compounds in chemistry and medicine. This proposal aims to develop three new unconventional approaches for the synthesis of boronic esters.The first one is based on the use of copper (low price and low toxicity) to promote unknown borylation reactions. Our method is an important step forward in that it proceeds using catalytic quantities of copper and allows the formation of a C-B bond along with a C-C or a C-N bond in a single catalytic cycle. Additionally, a copper-catalyzed borylation reaction is proposed as the key tool to solve the total synthesis of nigricanoside A, a potent antimitotic agent. The total synthesis of this natural product could have an impact in cancer research similar to that found for taxol or epothilones.The second approach deals with the development of borylation reactions under metal-free conditions. I propose to use bifunctional catalysts to promote the dual activation of B-B bonds and suitable electrophiles. This approach constitutes an unconventional way to synthesize boronic esters and has no precedent in the literature.Finally, the third section of this proposal branches into riskier territory. I propose to use Lewis-base/diboron adducts to generate organoboryl radicals. If successful, the potential impact will be very high and will certainly open unexplored ways in boron chemistry.The copper-catalyzed, metal-free, and radical approaches proceed by mechanistically distinct pathways and can give rise to complementary reactivity and selectivity partners. New findings in these areas would represent a significant step in the industrial and academic synthesis of boronic esters.