Synthesis of spirolactones by 1,3‐dipolar cycloadditions to methyl (<i>S</i>)‐3‐[(<i>E</i>)‐cyanomethylidene]‐2‐oxotetrahydrofuran‐5‐carboxylate

Abstract

Abstract Dedicated to Professor Emeritus Miha Tišler on the occasion of his 75th birthday Treatment of methyl ( S )‐5‐[( E )‐(dimethylamino)methylidene]‐2‐oxotetrahydrofuran‐5‐carboxylate ( 2 ) with potassium cyanide in acetic acid gave ( S )‐5‐[( E )‐cyanomethylidene]‐2‐oxotetrahydrofuran‐5‐car‐boxylate ( 3 ), which was used as chiral dipolarophile in 1,3‐dipolar cycloadditions. Reactions of 3 with diazomethane ( 4 ) and nitrile oxides 5a‐c afforded spirolactones 6–8 in 24‐34% diastereomeric excess, while with diazomethane ( 4 ) in the presence of triethylamine, methyl 3‐cyanomethyl‐2‐methoxyfuran‐5‐carboxylate ( 12 ) was obtained.