This week sees the publication of a new reagent, for the Julia−Kocienski olefination, from the group of Kendo at Gifu University, Japan:
It’s made by the obvious route in three steps and 92% overall yield.
It reacts well with para-methoxy acetophenone using t-BuOK in DMF to give the corresponding olefin in 93% yield after 1 hour at room temperature on a large (5mmol) scale. It reacts efficiently with a variety of aldehydes and ketones giving good to excellent yields of olefins. The side product, 1-methyl-1H-benzo[d]imidazol-2(3H)-one, is easily removed by a slightly basic work-up, or by chromatography, if required. Stability problems of the new reagent were observed in the presence of base, especially the one optimal for the required reaction! This was circumvented by preparing the N-iPr compound which behaved as the N-Me compound in its reaction with aldehydes and ketones. Stability tests showed that the N-iPr derivative is much more stable than the N-Me compound or indeed the standard Julia−Kocienski tetrazole sulfone. “In summary, we found that new methylenation reagents 1e and 1f react with a variety of aldehydes and ketones in the presence of t-BuOK in DMF at room temperature in 1 h to give terminal alkenes in high yields. The reagents can be prepared easily without any expensive reagents and the reaction conditions are mild and practical. We believe our new methylenation reagents are useful complements to the Wittig reagent CH3P(C6H5)3Br and other methylenation procedures. In order to expand the scope and utility, further study on this olefination reaction is presently under active investigation in this laboratory”.
This is a very useful paper, not only describing a new reagent, simple to make and use and importantly allows the easy purification of reaction mixtures. There is also a nice pictorial representation of the currently available Julia−Kocienski reagents along with the appropriate references which could save some library time.
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