Synthesis of cycloheptanones and higher homologues
Functionalized α-tertiary and -quaternary 2-arylcycloalkanones are rapidly accessed by scandium(III) triflate-catalyzed diazoalkane-carbonyl homologations. Pairing readily available bis- and tris(oxazoline) based ligands with scandium triflate allows access to arylated medium ring carbocycles with high enantioselectivities and excellent yield.
V. L. Rendina, H. Z. Kaplan, J. S. Kingsbury, Synthesis, 2012, 44, 686-693.
A highly diastereoselective insertion of α-alkyldiazoacetates to cyclohexanone and its heteroanalogues furnishes seven-membered rings with 1,4-quaternary-tertiary, 1,4-quaternary-quaternary, or 1,3,5-quaternary-tertiary-tertiary stereogenic centers in a single operation starting from readily available materials.
T. Hashimoto, Y. Naganawa, K. Maruoka, J. Am. Chem. Soc., 2009, 131, 6614-6617.
Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane gave zinc alkoxides of cis-5,6-dialkylcyclohepta-3,7-diene-1,3-diol in good yields at room temperature via a cis-divinylcyclopropane-1,2-diol and a subsequent Cope rearrangement. The reaction proceeded with high stereospecificity.
Y. Takada, K. Nomura, S. Matubara, Org. Lett., 2010, 12, 5204-5205.
Metal-catalyzed, regioselective [5 + 2] cycloadditions of vinylcyclopropanes and electron-rich alkynes (ynol ethers) provide dioxygenated seven-membered rings, a common feature of numerous natural and non-natural targets and building blocks for synthesis. The reactions proceed in high yield at room temperature and tolerate a broad range of functionalities.
P. A. Wender, C. Ebner, B. D. Fennell, F. Inagaki, B. Schröder, Org. Lett., 2017, 19, 5810-5813.
Rh-catalyzed [5 + 2] cycloadditions of 1-(2-methyoxyethoxy)-1-vinylcyclopropane as a five-carbon component to alkynes provide cycloheptenones in many cases in minutes and in very good isolated yields. The procedure is readily conducted on a small or large scale.
P. A. Wender, A. J. Dyckman, C. O. Husfeld, M. J. C. Scanio, Org. Lett., 2000, 2, 1609-1611.
A [6 + 2] annulation that involves the combination of β-alkenoyl acylsilanes and a vinyllithium derivative enables in one operation and a stereoselective manner the construction of eight-membered ring systems containing useful functionalities for further synthetic elaboration from readily available six- and two-carbon components.
K. Takeda, H. Haraguchi, Y. Okamoto, Org. Lett., 2003, 5, 3705-3707.
The reaction of β-keto esters with CF3CO2ZnCH2I provided the corresponding chain-extended products in moderate to good yields. α-Substituted acyclic β-keto esters reacted less efficiently than cyclic β-keto esters or simple β-keto esters.
S. Xue, Y.-K. Liu, L.-Z. Li, Q.-X. Guo, J. Org. Chem., 2005, 70, 8245-8247.
[ReBr(CO)3(thf)]2 catalyzes the reaction of a 1,3-dicarbonyl cyclic compound with an acetylene to give a medium-sized cyclic compound in excellent yield. By using isocyanide as an additive, the insertion of acetylenes into a carbon-carbon single bond occurs under mild conditions.
Y. Kuninobu, A. Kawata, K. Takai, J. Am. Chem. Soc., 2006, 128, 11368-11369.