The oxa-Pictet-Spengler reaction with various aldehydes and -arylethanol yields 1-substituted-isochromans in the presence of bismuth triflate as catalyst in good yields. The method was extended to O,O-acetals to afford the corresponding 1,1-disubstituted-isochromans in good yields. These studies also provide insights into the catalytic role of triflic acid generated upon hydrolysis of Bi(OTf)3 by residual water. The low toxicity and easy handling of Bi(OTf)3 by comparison with triflic acid make these procedures an attractive method to provide isochromans in good to excellent yields.
Synthesis of isochromans via Fe(OTf)2-catalyzed Oxa-Pictet–Spengler cyclization
作者:Jimei Zhou、Chao Wang、Dong Xue、Weijun Tang、Jianliang Xiao、Chaoqun Li
DOI:10.1016/j.tet.2018.10.028
日期:2018.12
Fe(OTf)2 has been found to be an efficient catalyst for the Oxa-Pictet–Spengler cyclization reaction leading to isochromans. A series of substituted isochromans were obtained with good to excellent isolated yields by coupling β-arylethanols with aldehydes or ketals under the catalysis of 1 mol% of Fe(OTf)2 at 70 °C. Using a cheap, less-toxic catalyst with water as the only byproduct, this iron-catalyzed