Acid, Silver, and Solvent-Free Gold-Catalyzed Hydrophenoxylation of Internal Alkynes

A range of arylgold compounds have been synthesized and investigated as single-component catalysts for the hydrophenoxylation of unactivated internal alkynes. Both carbene and phosphine-ligated compounds were screened as part of this work, and the most efficient catalysts contained either JohnPhos or IPr/SIPr. Phenols bearing either electron-withdrawing or electron-donating groups were efficiently added using these catalysts. No silver salts, acids, or solvents were needed for the catalysis, and either microwave or conventional heating afforded moderate to excellent yields of the vinyl ethers.

Microwave-Assisted Phospha-Michael Reactions with Internal Alkenes

The atom efficient phospha-Michael reaction between bis 4-methylphenyl phosphine oxide and several activated internal alkenes has been shown to occur under microwave irradiation without added solvent or catalyst. The alkenes used for this study were ethyl 4-nitrocinnamate, two chalcones ((E)-3-(4-methoxy-phenyl)-1-(4- nitrophenyl)-prop-2-en-1-one and (E)-1-(4-methoxyphenyl)-3-(3-nitro-phenyl)-prop-2- en-1-one), and 2-phenylmethylene-propanedinitrile. In the case of ethyl 4-nitrocinnamate, reaction with bis 4-methylphenyl phosphine oxide for sixty minutes at 130 °C yielded the desired phospha-Michael product in a 55% yield after purification. Varying the location of the nitro group on the phenyl rings of the chalcones did not seem to have a large effect on their reactivity. By NMR, both chalcones seemed to react to the same extent when the reaction times and temperatures were held constant. Interestingly, a phospha-Michael reaction was observed at a reaction temperature of 65°C for experiments involving 2- phenyl-methylene-propanedinitrile while the other substrates required a reaction temperature of 130 °C. Similar experiments were carried out with bis mesityl phosphine oxide and two internal alkenes: 2-phenylmethylene-propanedinitrile and ethyl-2-cyano-3- methyl-2-butenoate. These experiments did not yield any of the predicted phospha- Michael products, which suggest steric limitations to the Michael donor for this reaction.