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.