Catalyst and substituent effects on the rhodium(II)-catalysed intramolecular Buchner reaction

A study of the norcaradiene–cycloheptatriene equilibrium in a series of azulenones by NMR spectroscopy; the impact of substitution on the position of equilibrium

“…42,43,45,46 With substituents (R) in the linker chain of the diazoketones, the resulting azulenones can be formed in two diastereomeric forms. 42,43,45,46 With substituents (R) in the linker chain of the diazoketones, the resulting azulenones can be formed in two diastereomeric forms.…”

“…42,43,45,46 With substituents (R) in the linker chain of the diazoketones, the resulting azulenones can be formed in two diastereomeric forms. 36,42,48 The effect of substitution at the bridgehead position, R 2 (Scheme 4) has been demonstrated in compounds 6-13. 45,47 In many instances, and particularly with sterically demanding groups at position C-3, the azulenones are formed as single diastereomers.…”

“…22 Analogously, two trifluoromethyl groups on the azulenone framework, push the equilibrium almost entirely to the cycloheptatriene (Table 1, entry 4). 42 In addition the dynamic behaviour of methoxyl-substituted azulenones has been described. [23][24][25] With a CO 2 Me substituent, the norcaradiene structure is destabilised however, and cleavage of C1-C6 bond is induced by valence isomerisation (Table 1, entry 6).…”

Modern Organic Synthesis with α-Diazocarbonyl Compounds

“…301,304 Recent studies have demonstrated that the reactivity of the Rh(II) catalyst can dramatically alter the diastereoselectivity of the ensuing reaction; reduced diastereocontrol is observed for more reactive rhodium(II) carboxylate catalysts such as Rh 2 (pfb) 4 and Rh 2 (tfa) 4 . 303 However, this effect can be counteracted through the presence of bulky substituents at the 2-and 3-positions of the carbon chain. This allows aromatic addition reactions to proceed essentially independent of the catalyst in terms of efficiency and diastereocontrol.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…1006) in a process that involves C-H insertion followed by cyclization [1070] and a related preparation of carbazoles from indoles (2) ring expansion of α-diazo esters substituted by aminomethyl groups [1076]; (3) catalyst and substituent effects on intramolecular Buchner (cycloheptatriene from benzene) reactions involved α-diazo ketones [1077];…”