Synthesis of isochromans via Fe(OTf)2-catalyzed Oxa-Pictet–Spengler cyclization

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 Oxa-Pictet–Spengler reaction can be considered environmentally-friendly and atom-economic.     

A short enantioselective synthesis of (+)-eleutherin, (+)-allo-eleutherin and a formal synthesis of (+)-nocardione B

A short enantioselective synthesis of (+)-eleutherin, (+)-allo-eleutherin and the formal synthesis of (+)-nocardione B is described. The synthesis is completed in six steps in overall yields of 8% for eleutherin and 14% for allo-eleutherin. The synthetic strategy features an efficient combination of the Dötz annulation reaction with a chiral alkyne and an oxa-Pictet Spengler reaction as the keys steps in the stereodivergent synthesis of (+)-eleutherin and (+)-allo-eleutherin. The synthesis of (S)-(+)-2-(2′-hydroxypropyl)-5-methoxy-1,4-naphthoquinone entails the formal synthesis of (+)-nocardione B.