Acid‐Catalyzed Conversion of 7‐Ethynyl‐ and 7‐Vinylcyclohepta‐1,3,5‐trienes to Substituted Benzene Derivatives

Abstract

The acid-catalyzed rearrangement in THF/TFA (5:1, v/v) of cyclohepta-1,3,5-trienes containing an α,β-unsaturated substituent at C-7 was investigated. 7-Ethynylcyclohepta-1,3,5-triene (1a) and its 1,4-di-tert-butyl (1b), 1,5-di-tert-butyl (1c), and 2,5-di-tert-butyl (1d) derivatives underwent isomerization to phenylallenes 2, 3, 7, and 3, respectively. 2,5-Di-tertbutyl-7-vinylcyclohepta-1,3,5-triene (17) gave a mixture (66:34) of (E)-and (Z)-1,4-di-tert-butyl-2-(1-propenyl)benzene (20). A mechanism involving the protonation of the norcaradiene tautomer (NCD), which is in equilibrium with cycloheptatriene (CHT) 1 or 17, followed by the cleavage of a three-membered ring to give an arenium ion, is proposed. In contrast, 2,5-di-tert-butyl-7-cyanocyclohepta-1,3,5-triene (12) and bis(cyclohepta-2,4,6-trien-1-yl)ethyne (21) did not

Insights into the Reaction Behaviour of Stannylated Allylic Substrates

“…As expected, no reaction occurred either with (Me 3 Si) 2 , but in this case we were able to isolate the substituted allene 21, [40] clearly indicating that the decomplexation of the allene is much faster than the disilylation. In the absence of any bismetal species, the allene 21 was obtained in excellent yield.…”

Stereoselective cis-Vinylcyclopropanation via a Gold(I)-Catalyzed Retro-Buchner Reaction under Mild Conditions

“…30b,36 In addition, we have found that alkenyl trifluoroborates can also be used as softer nucleophiles, which allow performing the addition reaction at room temperature in DMF. 37 …”

“…Alkenylcycloheptatrienes 1 can be obtained by the reaction of alkenyllithium or Grignard reagents with tropylium salts. , In addition, we have found that alkenyl trifluoroborates can also be used as softer nucleophiles, which allow performing the addition reaction at room temperature in DMF…”

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

“… 49 The reaction of 7-ethynylcyclohepta-1,3,5-triene with trifluoroacetic acid leads to phenylallene by protonation of the alkyne in the norcaradiene tautomer followed by cyclopropane cleavage to form the arenium cation. 50 The reaction of 7-ethoxycarbonyl-1,3,5-cycloheptatriene with an equimolecular amount of Pd(OAc) 2 at 80 °C in MeCN had been reported to give ethyl 2- and 4-formylbenzoate (8% each) by cleavage of one cyclopropane C–C bond of the corresponding norcaradienes. 51 In addition, diethyl maleate (14% yield) was formed, presumably by a dimetization of a Pd(II) carbene formed by a retro-Buchner process.…”