From Prof. Hideki Yorimitsu's and Koichiro Oshima's group at Kyoto University, Japan
Another Org Lett ASAP this month. This one deals with chromium-catalyzed arylmagnesiation of alkynes.
During the screening process for the optimal reaction conditions using 1 and 2, protic additive was found to be essential. For this purpose, carboxylic acid was found to work best. The bulkiness of the acid was crucial for a successful reaction and thus tBuCOOH was identified as an optimal additive. This acid additive could catalyze the reaction to a much faster rate while improving yield and E/Z selectivity.
The scope of the reaction was investigated and the results are summarized below. A variety of arylmagnesium bromide could couple stereoselectively with various alkynes to give, after quenching with water, desired alkenes.
In addition, the new intermediate alkenylmagnesium bromide, such as 4, was shown to undergo various typical trapping/subsequent reactions of Grignard reagents to provide a variety of products in good to excellent yields and selectivities (Scheme 1).
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