Synthesis of cyclobutanes
Suitable conditions enable the Suzuki-Miyaura coupling reaction of potassium cyclopropyl- and cyclobutyltrifluoroborates in moderate to excellent yield with electron-rich, electron-poor, and hindered aryl chlorides to give various substituted aryl cyclopropanes and cyclobutanes.
G. A. Molander, P. E. Gormisky, J. Org. Chem., 2008, 73, 7481-7485.
(E)- and (Z)-silyl and aryl-subsituted homoallylic methanesulfonates were converted to the corresponding cis- and trans-1-silyl-2-borylcyclobutanes as well as 1-phenyl-2-borylcyclobutanes in the presence of a CuCl/dppp catalyst, bis(pinacolato)diboron, and K(O-t-Bu)in THF. Stereospecific derivatizations of the cis- and trans-borylcyclobutanes were carried out to demonstrate the utility of the borylcyclobutanes.
H. Ito, T. Toyoda, M. Sawamura, J. Am. Chem. Soc., 2010, 132, 5990-5992.
A diverse range of unsymmetrical tri- and tetrasubstituted cyclobutane structures can be produced in good yields and excellent diastereoselectivities using an efficient [2+2] heterodimerization of dissimilar acyclic enones upon visible light irradiation in the presence of a ruthenium(II) photocatalyst. The reaction is promoted by any visible light source.
J. Du, T. P. Yoon, J. Am. Chem. Soc., 2009, 131, 14604-14606.
Ru(bipy)3Cl2 is a visible light photocatalyst for [2+2] enone cycloadditions. Various aryl enones participate readily in the formation of the cyclobutane products, and the diastereoselectivity is excellent. A mechanism is proposed in which a photogenerated Ru(bipy)3+ complex promotes one-electron reduction of the enone substrate, which undergoes subsequent radical anion cycloaddition.
M. A. Ischay, M. E. Anzovino, J. Du, T. P. Yoon, J. Am. Chem. Soc., 2008, 130, 12886-12887.
Angle strain in methylene cyclobutane drives a cross-enyne metathesis with 1-alkynes, giving 1,1,3-trisubstituted 1,3-dienes in good isolated yields. An extensive survey of Grubbs’ second-generation catalysts led to optimized reaction conditions.
D. A. Clark, B. S. Basile, W. S. Karnofel, S. T. Diver, Org. Lett., 2008, 10, 4927-4929.