Utilization of Baylis-Hillman Adducts in palladium catalyzed reactions: mechanistic studies concerning the Baylis-Hillman reaction employing ESI-MS (/MS)

Author(s)

Cesar Henrique Pavam

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2005-01-03

Examining board members

Fernando Antonio Santos Coelho; Simon John Garden; Carlos Roque Duarte Correia

• Advisor: Fernando Antonio Santos Coelho

Abstract

The present work can be separated in two distinct parts, both concerning the chemistry of Baylis-Hillman adducts. The first part deals wíth the reactivity of these molecules facing palladium complexes in catalytic reaction conditions. In this way, we have employed aromatic orto halogenated Baylis-Hillman adducts as substrates for intramolecular Heck reactions, in severaI reaction conditions, aiming the construction of indanic frameworks. However, the expected products were not obtained at all in most of the studied catalytic systems. Probably, the 5-endo-trig cyclization model, kinetically disfavored, has been disfavored our approach. In continuation of this work, we employed these same substrates in cyclocarbonylation reactions catalyzed by Pd-tri-tert-butylphosphine type complexes in basic media, owing the synthesis of highly functionalized enol lactones. With this approach, we were able to synthesize severaI phtalides (with different steric and electronic properties), a cyclohexanone derivative, a b-spiro-Iactone moiety, as well an allylic alcohol compound, in good to excellent yields. These reactions proceed accordingly essentially different tandem transformations catalyzed by palladium (cyclocarbonylation/isomerization in the case of phtalides and double chemoselective cyclocarbonylation in the case of the b-spiro-Iactone). In the specific case of the phtalides, the cyclization model 5-exo-trig was observed, explaining therefore the dichotomy in the reactivity between the aryl- and acyl palladium complexes derived from the same Baylis-Hillman adducts precursors. The second part of the present Dissertation deals with the mechanistic study of the Baylis-Hillman reaction employing mass spectrometry with electrospray ionization (ESI-MS), as well as tandem mass spectrometry (ESI-MS/MS). This approach allowed us to probe, for the first time, the mechanism of this reaction, through the detection and structural characterization of all the zwitterionic intermediates involved in the catalytic cycle of the Baylis-Hillman reaction, in their protonated forms in methanolic solution. (AU)