Once again, the product 3a was isolated in a moderate yield of 58% and only in the presence of a significant excess of 2b and indium ( Table 1, entries d–g). Successively, the growing use in the literature of indium as an efficient metal for promoting the Barbier reaction (8) spurred us to investigate the synthesis of 3a starting from allyl bromide 2b and 1a. No improvement was observed by changing the solvent ( Table 1, entries a–c). The reaction gave a modest result, and 3a was isolated in 56% yield. Based on the article of Kalita and Phukan relating to the allylation of chalcones, (7) we first attempted the conversion of 1a into 3a using allyltributylstannane 2a in the presence of CuI (0.25 equiv) and DMF.
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