Brønsted Acid Promoted Thermal‐Ring‐Rearrangement of Fluorenopyrans to 2‐(1H‐Inden‐3‐yl)‐9H‐fluoren‐3‐ols Bearing Two All‐Carbon‐Quaternary Centres

Abstract

4-Aryl-fluorenopyrans bearing quaternary centre at C2 and C6 positions underwent a thermal-ring-rearrangement with a catalytic amount of pTsOH to furnish 2-(1H-inden-3-yl)-9H-fluoren-3-ols with two all carbon-quaternary centres, in which one is retained and the other is created. Interestingly, these compounds exhibit atropisomerism, when they have at [a] Figure 2. Acidochrmoic nature of 1a. Results and DiscussionTo find out the suitable reaction conditions of the ring-rearrangement reaction, we have selected 5,11-dimethyl-2,2,4,6,6- Table 1. Substrate scope of fluorenopyrans in TRR.[a] Conditions: All reactions were performed in a 0.15 mmol scale; [b] isolated as a mixture of diastereomers.

Cu-Catalyzed Oxidative C(sp2)–H Cycloetherification of o-Alkenyl Arenols for the Preparation of Fused Furans

“…We commenced our study by examining the intramolecular C­(sp 2 )–H oxacyclization of 1-(1,1-dimethyl-1 H -inden-3-yl)­naphthalen-2-ol ( 1a ) (which was prepared using a reported method) to 8,8-dimethyl-8 H -indeno­[2,1- b ]­naphtho­[1,2- d ]­furan ( 2a ). A detailed study of reaction conditions indicated that heating 1a in 1:1 DMSO/AcOH at 140 °C with 10 mol% CuI in an open flask furnished the maximum yield of 2a , 92% (Table ).…”