46 One Step Synthesis of Michael Acceptors by An Organocatalyst

Wednesday, November 4, 2009: 11:40 AM
Rio Grande (Camino Real Hotel)
Alejandro Bugarin , Chemistry, Texas A&M University, College Station, TX
Brian T. Connell , Chemistry, Texas A&M University, College Station, TX
Molecules incorporating the α,β-unsaturated carbonyl functionality are commonly utilized as substrates for a range of chemical transformations, including the Morita–Baylis–Hillman reaction, the Diels–Alder reaction, Michael additions, in addition to numerous biotransformations.
This objective of this study was to develop a rapid, convenient, one step α-methylenation of a variety of carbonyl-containing molecules. Herein we report a simple and mild protocol for the direct α-methylenation of aldehydes, ketones and esters using paraformaldehyde, a stoichiometric amount of N-diisopropylammonium trifluoroacetate, and 10 mol% trifloroacetic acid in refluxing tetrahydrofuran. This reaction affords α,β-unsaturated carbonyls by way of a Mannich-type reaction of a transiently formed Schiff base.
Using this catalytic system, α,β-unsaturated carbonyls can be obtained in good to excellent yields (62 to 99%) using various aromatic and aliphatic ketones, aldehyes and/or esters at 67 ºC after 8 h (18 examples). Furthermore, no isomerization of the double bond is detected in any of the adducts. The TBDPS protecting group is shown to be stable to these reaction conditions.
In conclusion the α-methylenation of carbonyls by N-diisopropylammonium trifluoroacetate and paraformaldehyde has been successfully accomplished. The ease with which this reaction can be performed could facilitate its use in numerous synthetic procedures including tandem processes.
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