Tetrabutylammonium Fluoride (TBAF) Promoted Some New Organic Synthesis Reactions And Fluorination Of β-halo-α, β-unsaturated Aldehydes Or Ketones

Carbon-carbon bond formation is of fundamental importance in organic synthesis. It lies at the heart of the synthetic organic chemistry and gives rise to an enormous number of molecular forms. Various methodologies are developed toward this target. The innovations in organic chemistry which use readily available, cheap and non-toxic materials to construct targeted molecules with high yields under mild conditions are highly desired. Therefore, development of new reaction and new methodology is one of the most attractive areas in organic chemistry.This dissertation is focused on the study of activations of cyclic and acyclicβ-halo-α,β-unsaturated aldehydes or ketones promoted by TBAF under mild conditions. The TBAF directly abstracts a proton at the gamma position from cyclicβ-halo-enal or enone to generate vinylogous enolate in solvent, whereas deprotonation of acyclic P-halo-enal at alpha position leads to elimination reaction. Two or three new methods have been developed for the additions ofβ-halo-α,β-unsaturated aldehydes or ketones with different electrophiles and a series of densely functionalized products have been prepared. Another study on fluorination of acyclicβ-halo-enal indicates elimination-addition mechanism for this nucleophilic substitution reaction instead of addition-elimination mechanism. The details are summarized below:1) A new Br(?)nsted base promoted method for the intermolecular crossed-conjugate addition between two different activated alkenes under mild conditions is described. This method facilitates the construction of all-carbon quaternary centers and synthesis of multi-functional spirocyclic compounds.2) A novel tandem deprotonation/Michael addition/acetalization reaction of two different enals is described. A functionalized spiro-2H-pyran derivative involving a quaternary carbon center and adjacent vinyl halogen group in the skeleton is readily synthesized through this highly selective crossed-Michael addition.3) A first direct vinylogous aldol reaction between cyclicβ-halo-enals and aromatic aldehydes promoted by TBAF to give polyfunctionalized 8-hydroxy-β-halo-α,β-unsaturated aldehydes in high regio-and diastereoselectivities under mild conditions is achieved.4) A highly efficient stereoselective synthesis of (Z)-monofluoroenals from acyclicβ-halo-enals in the presence of TBAF in THF under mild conditions is described. In practice, it is a tandem elimination-addition reaction.