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Ring-Expansion

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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.

The use of an oxazaborolidinium ion catalyst enables a highly stereoselective synthesis of (Z)-silyl enol ethers from alkyl aryl ketones and trimethylsilyldiazomethane (TMSD). The conversion of cyclic ketones gives ring-expanded silyl enol ethers.
B. Chul, Kang, S. Y. Shim, D. H. Ryu, Org. Lett., 2014, 16, 2077-2079.

The homologation of arylcyclobutanones with trimethylsilyldiazomethane gives enolsilanes in the presence of Sc(OTf)₃ as catalyst with a high preference for methylene migration, whereas Sc(hfac)₃ leads to β-ketosilanes. Each adduct affords the cyclopentanone upon hydrolysis.
J. A. Dabrowski, D. C. Moebius, A. J. Wommack, A. F. Kornahrens, J. S. Kingsbury, Org. Lett., 2010, 12, 3598-3601.

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.

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 chiral Al(III)-N,N'-dioxide complex catalyzes an acyloin rearrangement of cyclic α-ketols to provide an array of optically active 2-acyl-2-hydroxy cyclohexanones in good yields with high enantioselectivities. Asymmetric isomerizations of acyclic α-hydroxy aldehydes and α-iminols were achieved as well under modified conditions.
L. Dai, X. Li, Z. Zeng, S. Dong, Y. Zhou, X. Liu, X. Feng, Org. Lett., 2020, 22, 5041-5045.

A combination of visible light photocatalysis and gold catalysis provides an entry into functionalized cyclic ketones from the coupling reaction of alkenyl and allenyl cycloalkanols with aryl diazonium salts via ring expansion-oxidative arylation. A mechanism involving generation of an electrophilic gold(III)-aryl intermediate is proposed.
X.-Z. Shu, M. Zhang, Y. He, H. Frei, F. D. Toste, J. Am. Chem. Soc., 2014, 136, 5844-5847.

A mild and operationally simple visible light mediated photocatalytic arylation/ring expansion of alkenylcyclobutanols in the presence of aryldiazonium salts provides functionalized cyclic ketones.
S. J. Kwon, D. Y. Kim, Org. Lett., 2016, 18, 4562-4565.

A gold(I)-catalyzed oxidative rearrangement of propargyl alcohols provides an efficient and selective route to 1,3-diketones under mild conditions in the presence of pyridine-N-oxides as external oxidants.
A. S. K. Hashmi, T. Wang, S. Shi, M. Rudolph, J. Org. Chem., 2012, 77, 7761-7767.

A stereospecific gold(I)-catalyzed rearrangement of 1-alkynyl cyclobutanols and cyclopropanols provides alkylidene cycloalkanones. The reaction tolerates terminal alkynes as well as alkyl, aryl, and halo-substitution at the acetylenic position and substituents on the ring.
J. P. Markham, S. T. Staben, F. D. Toste, J. Am. Chem. Soc., 2005, 127, 9708-9709.

Oxidative ring expansion of methylenecyclopropanes with CAN under oxygen atmosphere was investigated. A facile conversion affording 2,2-diarylcyclobutanones occurred in good yields.
V. Nair, T. D. Suja, K. Mohanan, Synthesis, 2006, 2531-2534.

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.

[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.