Transition-Metal-Catalyzed Rearrangements of Small Cycloalkanes: Regioselectivity Trends in β-Carbon Elimination Reactions

Abstract

In this review, the regioselectivity of transition-metalcatalyzed ring cleavage of cyclopropanes and cyclobutanes by bcarbon elimination is analyzed using experimental results and rationalization models from the literature. Most models proposed are generally consistent with the following trends: Cleavage of the less substituted bond of the small cycloalkane is favored by a minimization of steric hindrance, whereas cleavage of the more substituted bond becomes possible if steric hindrance is limited and if the substituent is electron-withdrawing or if it can coordinate the metal. Importantly, steric congestion can easily offset electronic activation. Moreover, regioselectivity models appear to be more generally applicable to cyclopropanes than to cyclobutanes.

Stereospecific ring expansion from orthocyclophanes with central chirality to metacyclophanes with planar chirality

“…No other diastereomer was detected in the crude reaction mixture. The (trimethylsilyl)methyl substituent and the C-C bond newly formed between the arene and 3 were assigned as trans to each other by a series of NMR analyses ( 1 H, 13 C, DEPT, COSY, HMQC, HMBC and NOESY).…”

“…Carbon-carbon (C-C) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and carbon-hydrogen (C-H) bonds [16][17][18][19][20][21][22][23][24][25] , which are ubiquitous in organic compounds, are intrinsically difficult to activate owing to their thermodynamic stability as well as their kinetic inertness. Selective transformation of such nonpolar s-bonds has provided a challenge that has motivated and inspired chemists to seek ways to activate these bonds over the past two decades.…”

Construction of Azabicyclo[6.4.0]dodecatrienes Based on Rhodium(I)-Catalyzed Intramolecular [6+2] Cycloaddition between Azetidine, Allene, and Alkynes

“…IR spectra were measured with a SHIMADZU FTIR-8700 spectrometer for samples in CHCl 3 or with a Thermo Scientific Nicolet iS5 FT-IR spectrometer. H-NMR spectra were measured with JNM-ECS400 or JNM-ECA600 spectrometers for samples in chloroform-d (CDCl 3 ).…”

“…[1][2][3][4][5] We recently disclosed that the rhodium(I)-catalyzed cycloaddition of allenylcyclopropanealkynes 1 (n=0) afforded the bicyclo[5.4.0] undecatrienes 2 (n=0) 6) in the [5+2] ring-closing manner (Chart 1). The reaction must have proceeded via cleavage of the cyclopropane ring due to the relief of its high strain energy (27.5 kcal/mol).…”

“…The unfunctionalized simple cyclobutane ring is generally known not to open, let alone being used as a C 4 -building block. [1][2][3][4][5] We tentatively interpreted that the production of 2 (n=1) would initiate the formation of the rhodabicyclo[4.3.0] intermediate 3 (n=1), [8][9][10] which should be susceptible to β-carbon elimination, [1][2][3][4][5] with release of the ring strain energy (26.3 kcal/mol) 11) giving rise to the nine-membered rhodabicyclic species 4. Reductive elimination would occur to provide the final products.…”