Addition of boron enolates of methylketones to aldehydes ; Intra and intermolecular hydrogen bonds in alkyl and silyl ethers: experimental and theoretical analysis

Author(s)

Marco Antonio Barbosa Ferreira

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2008-07-31

Examining board members

Luiz Carlos Dias; Jose Daniel Figueroa Villar; Antonio Claudio Herrera Braga

• Advisor: Luiz Carlos Dias

Abstract

ADDITION OF BORON ENOLATES OF METHYLKETONES TO ALDEHYDES. The presence of a b-heteroatom substituent in the boron enolates of methylketones has a strong influence in the stereochemical outcome of the corresponding aldol reactions. The boron-mediated aldol reactions of methylketones with P = PMB were found to proceed with high degrees of remote 1,5-anti stereoinduction. In the case of methylketones with P = TBS and P = t-Bu, the corresponding boron enolates additions to aldehydes gives a mixture of aldol adducts favoring the 1,5-syn adducts. The nature of the substituent at the aromatic ring does not influence the stereochemical outcome, as p-OMe and p-NO2 lead to similar results.INTRA AND INTERMOLECULAR HYDROGEN BONDS IN ALKYL AND SILYL ETHERS: EXPERIMENTAL AND THEORETICAL ANALYSIS. We have investigated the electronic impact of the P protecting group (TBS or PMB) in the conformational equilibrium of (R)-methyl substituted alcohols 139 (P = TBS) and 140 (P = PMB). The conformational analysis and H NMR experiments for alcohols 139 and 140 reflect the tendency for the existence of hydrogen-bonded conformations. We showed that the extents of the hydrogen bonds in silyl and alkyl ethers are determined by several properties, such as orbital interactions, lone pair hybridizations, and lone pair energies, and not just by the electronic occupancy of the acceptor atom (AU)