Synthesis of Baylis-Hillman adducts (enones)
An efficient method for the synthesis of multifunctionalized alkenes has been developed. In the presence of 5 mol% CuI as catalyst, an organozinc species CF3COOZnR reacted with α,β-acetylenic ketones and aldehydes in one pot providing trisubstituted alkenes in high yields with high stereoselectivity. The reaction with β-substituted-α,β-acetylenic ketones gave tetrasubstituted alkenes in good yields with Z-isomers as the major products.
S. Xue, L. He, Y.-K. Liu, K.-Z. Han, Q.-X. Guo, Synthesis, 2006, 666-674.
A Ba-catalyzed dynamic kinetic asymmetric transformation (DYKAT) involving a direct aldol/retro-aldol reaction of a β,γ-unsaturated ester with various aldehydes and an isomerization under simple proton-transfer conditions allows the synthesis of α-alkylidene-β-hydroxy esters with high enantio- and regioselectivity.
A. Yamaguchi, S. Matsunaga, M. Shibasaki, J. Am. Chem. Soc., 2009, 131, 10842-10843.
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 Morita-Baylis-Hillman reaction.
T. E. Reynolds, C. A. Stern, K. A. Scheidt, Org. Lett., 2007, 9, 2581-2584.
Silyloxyallenes derived from α-hydroxypropargylsilanes add efficiently to aldehydes with catalytic amounts of Lewis acids. The allenes are accessed from the corresponding propargylsilanes in a base-catalyzed 1,2-Brook rearrangement/SE2' process. Conversion to the silyloxyallenes occurs with minimal erosion in optical activity.
T. E. Reynolds, A. R. Bharadwaj, K. A. Scheidt, J. Am. Chem. Soc., 2006, 128, 15382-15383.
A stereoselective multicomponent synthesis of (Z)-β-bromo Baylis-Hillman ketones uses MgBr2 as both the Lewis acidic promoter and the bromine source for the Michael-type addition with α,β-acetylenic ketones to form an active β-bromo allenolate intermediate, which in turn attacks various aldehydes to afford β-bromo Baylis-Hillman adducts in good yields and Z-selectivity.
H.-X. Wei, R. L. Jasoni, J. Hu, G. Li, P. W. Pare, Tetrahedron, 2004, 60, 10233-10237.
A simple and highly stereoselective method has been developed for the synthesis of (Z)-β-iodo Baylis-Hillman adducts using CeCl3·7H2O/NaI as an inexpensive and readily available reagent system.
J. S. Yadav, B. V. S. Reddy, M. K. Gupta, B. Eeshwaraiah, Synthesis, 2005, 57-60.