Nucleophilic boryl motifs and alpha-borylcarbanions: reactivity and trends

Identifier:  TDX:3712

Handle: https://hdl.handle.net/20.500.11797/TDX3712

Authors:  Maza Quiroga, Ricardo José

Abstract:
In Chapter 2, copper (I) catalyzes the borylative cyclization of gamma-alkenyl aldehydes through chemo- and regioselective addition of Cu-B to C=C and concomitant intramolecular 1,2-addition of Cu-C on the C=O. The products are formed in an exclusive diastereoselective manner and computational analysis identify the key points for the chemo- and diastereoselectivity observed. In Chapter 3, we study the reactivity of diboron reagents with 1,3-dienes in a transition-metal-free context. The sole addition of Na2CO3 to bis(pinacolato)diboron, in MeOH, allows the 1,4-hydroboration of cyclic and noncyclic 1,3- dienes. The electronic influence on the substrate guarantees the conjugated 1,4-hydroboration versus 1,2-diboration. DFTcalculations show that the distribution of charge in the allylic anion intermediate governs the selectivity toward 1,4- hydroboration, while the favored trans configuration in diene reagents determines the preference for the E allyl boronate products. In Chapter 4, we studied the chemistry of alpha-boryl carbanions since they show a remarkable diversity, and enable efficient C-C bond formation. The electron-deficient, trivalent boron center stabilizes the carbanion facilitating its generation and tunning its reactivity. We describe the electronic structure and the reactivity trends of a large dataset of apha-boryl carbanions. We use DFT-parameters for capturing their electronic and steric properties, computational reactivity towards model substrates, and crystallographic analysis within the Cambridge Structural Dataset. This study maps the reactivity space by systematically varying the nature of the boryl moiety, the substituents of the carbanionic carbon, the number of alpha-boryl motifs, and the metal countercation. Furthermore, we can classify the alpha-boryl alkylidene metal precursors into three classes directly related to their reactivity. This trend map aids the selection of the appropriate reactive synthon depending on the sought reactivity.