Highly substituted α,β-unsaturated ketones are prepared by the N-heterocyclic carbene-initiated addition of α-hydroxypropargylsilanes to aldehydes. This strategy serves as a highly efficient alternative to the standard Morita-Baylis-Hillman (MBH) approaches for these types of compounds. In contrast to the MBH reaction, different substitution in the β-position of the product (R 1 ) can be accommodated in moderate to excellent yields with a high degree of control over the resulting alkene.The Morita-Baylis-Hillman (MBH) reaction is an efficient reaction that generates highly functionalized compounds by employing α-acylvinyl anion reactivity. 1 Significant advances in the MBH reaction have been made recently, including mechanistic studies as well as asymmetric and intramolecular variants. 2,3 Despite this progress, the intermolecular MBH reaction has intrinsic limitations. In particular, the β-substituents of the activated alkene starting materials (e.g., ethyl acrylate, vinyl ketones) are almost always hydrogen atoms. Recently, we reported the scandium(III)-catalyzed addition of silyloxyallenes to aldehydes as a valuable alternative to the MBH and other α-acylvinyl anion processes (Option I, Figure 1). 4-6 These reactions proceed under very mild conditions (10 mol % Sc(OTf) 3 ) and accommodate a wide scope of β-substitution with excellent yields and a high degree of control over the resulting alkene geometry. Also, enantioenriched products could be synthesized by the (-)-(salen)Cr (III)-catalyzed additon of racemic silyloxyallenes. 4 One aspect of the transformation is the prerequisite of preparing the silyloxyallenes in a separate step through the Kuwajima-Reich rearrangement of the α-hydroxypropargylsilane precursors. 7 Herein, we present an alternative single-flask approach starting directly from the propargylsilanes, thus further enhancing the applicability of this unconventional α-acylvinyl addition reaction (Option II, Figure 1).Our current interests include the development of reactions employing Lewis base activation to efficiently access unconventional reactivity. Several transformations from our laboratory, including acyl anion additions, homoenolate reactions, alkyne additions, disilylations of activated alkenes, and hydroacylations of ketones have been facilitated by the use of Lewis bases. 8 Given our strong interest in the combination of Lewis basic promoters/catalysts, we reasoned that Lewis bases may activate silyloxyallenes toward addition. In particular, they scheidt@northwestern.edu. Supporting Information Available: Experimental procedures and spectral data for all new compounds, and a CIF file for H14·Cl. This material is available free of charge via the Internet at http://pubs.acs.org. should be more compatible with the rearrangement conditions (substoichiometric n-BuLi, THF) of the α-hydroxypropargylsilanes to the allenes and facilitate a single flask procedure. NIH Public AccessStarting with α-hydroxypropargylsilane 1 in THF at 0 °C, the allene was formed with use of 5 mol % of n-B...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.