80213-82-7Relevant academic research and scientific papers
Mechanistic studies on the reaction of fischer carbene complex with alkynes: Does the alkyne insertion intermediate form irreversibly?
Waters, Marcey L.,Bos, Mary E.,Wulff, William D.
, p. 6403 - 6413 (1999)
The regioselectivity of the formation of three different products from the reaction of 1-phenylpropyne with (methoxy)(2-methoxyl-1-phenyl)methylene pentacarbonyl chromium 12 was examined in detail. The phenol product is formed with a substantial regioselectivity which is temperature-dependent, but the indene products (obtained as two compounds: indene and indenone) are formed as a nearly equal mixture of regioisomers. The proportion of indene and phenol products is dependent on the concentration with greater amounts of phenol products being formed at higher concentrations. The total regioselectivity of all of the products is also a function of the concentration. This result could be due either to an equilibration of the η1,η3-vinyl carbene intermediates in this reaction or to a change in mechanisms in the formation of the η1,η3-vinyl carbene intermediates from one involving a dissociative incorporation of the alkyne to one involving an associative incorporation of the alkyne. Kinetic studies reveal that at 45 °C and at 0.5 M (but not 0.0001 M) the reaction is bimolecular with a first-order dependence on both the carbene complex and the alkyne. However, at 90 °C the reaction is first-order in carbene complex and zero-order in alkyne over the concentration range of 0.05-0.005 M where the total regioselectivity changes from 2.5:1.0 to 1.5:1. This observation constitutes the first experimental evidence for the equilibration of regioisomeric vinyl carbene intermediates during the benzannulation reaction. This equilibration could occur as a result of a deinsertion of the alkyne or via a cyclopropene intermediate. Finally the generality of the unprecedented bimolecular reaction of complex 12 with 1-phenylpropyne at high concentrations was examined for the reaction methoxy(phenyl)methylene pentacarbonyl chromium 28 with diphenylacetylene and phenylacetylene at 0.5 M, and it was found that both reactions are first-order in carbene complex only.
A Strategy for Generalization of the Regiospecific Synthesis of Substituted Quinones from Cyclobutenediones
Liebeskind, Lanny S.,Granberg, Kenneth L.,Zhang, Jing
, p. 4345 - 4352 (2007/10/02)
Documented within is a straightforward protocol for the synthesis of generally substituted benzoquinones and ring-fused quinones.Previously, the crucial issue of quinone substituent regiochemistry was resolved at the stage of addition of an unsaturated carbon nucleophile to a cyclobutenedione by using either symmetrically substituted cyclobutenediones or 3-alkoxy (or amino)-4-substituted-3-cyclobutenediones.In the former case there are no regioisomeric quinones formed, while in the latter, through resonance delocalization, the alkoxy (or amino) substituent renders one of the two carbonyl groups less reactive and directs the incoming nucleophile to the other.The placement of a wide variety of substituents about the quinone ring periphery has now been solved by the less restrictive strategy of sequential introduction of substituents onto a cyclobutenedione core.The chemistry commences with 3-isopropoxy-4-substituted-3-cyclobutene-1,2-diones.Addition of an aromatic, heteroaromatic, or alkenyl nucleophile to the more reactive carbonyl group provides 4-hydroxy-4-Runsat-2-cyclobutenones, which are protected as the methyl ethers by treatment with MeI/Ag2O/K2CO3 in MeCN.A second nucleophile is added, again in a 1,2-sense, providing highly substituted 3-isopropoxy-2-cyclobutenols that are arranged to cyclobutenones under acidic conditions.The resulting cyclobutenones are converted into substituted quinones by thermolysis at 140 deg C in o-xylene followed by oxidative workup with ceric ammonium nitrate.The substitution pattern about the quinone core is rigorously controlled by the sequence of introduction of the substituents.
