POTENTIALLY AROMATIC THIOPHENIUM YLIDES .5. REACTIONS OF ETHOXYCARBONYL-2-(2-THIENYL)PHENYLCARBENE (AND METHOXYCARBONYL)-2-(2-THIENYL)PHENYLCARBENE

In an attempt to make thiophenium ylides in which the ylide bond is part of a five-membered ring annulated to the a-side of the thiophene moiety, two alkoxycarbonyl substituted 2-(2-thienyl)phenylcarbenes have been made, with and without chlorine substituents in the remaining thiophene positions. With rhodium acetate as a catalyst the carbene without chlorines cyclized to the 3-position of the thiophene to give a fluorene analogue, whereas no cyclization was detected when the 3-position was blocked.