Step 1. Condensation of arylindanones with diethyl oxalate

Compounds **10a**,**b**,**d**,**e**: Corresponding indanone (9.6 mmol, 1 equiv.) and diethyl oxalate (4.2 g, 3.9 mL, 28.8 mmol, 3 equiv.) were dissolved in THF (10 mL, dry) in a roundbottom flask, and to the resulting solution a suspension of *t*-BuOK (3.23 g, 28.8 mmol, 3 equiv.) in THF (15 mL, dry) at room temperature was added dropwise. Next, the flask was stoppered, and the mixture was heated in a metal heating block at 65 ◦C for 72 h (conversion was estimated by TLC, using DCM as an eluent). After cooling to room temperature, the solvent was evaporated and the mixture was dissolved in CHCl3 (30 mL), washed with 3% hydrochloric acid solution (1 × 15 mL), water (1 × 15 mL) and brine (1 × 15 mL), then organic layer was dried over anhydrous sodium sulfate. The solvent was evaporated, and the resulting mixture was used in the next step without purification. Compounds **10c**,**f** were obtained according to nearly the same procedure (but using *t*-BuOLi instead of *t*-BuOK), and the heating was performed for 16h.

#### Step 2. Oxidation

A solution of KOH (3.76 g, 67.2 mmol, 7 equiv.) in water (20 mL) was added to the product of the previous step in a round-bottom flask; the mixture was stirred for 20 min, then H2O2 (30%, 27.2 mL) was added dropwise. The solution was stirred overnight at room temperature, then heated in a metal heating block to 50 ◦C and stirred for two hours (until the mixture became transparent). Activated charcoal (12 g) (powder−100 particle size (mesh)) was added to the resulting chilled solution and intensively stirred for 15 min. The solution was filtered through zeolite, and a solution of concentrated hydrochloric acid was added to the filtrate at room temperature to reach pH 1. The precipitated acid was extracted into EtOAc (3 × 30 mL). The organic layer was combined, dried over anhydrous sodium sulfate and evaporated. The resulting acids **10a**–**e** did not require further purification. The acid **10f** was additionally crystallized from acetonitrile. Yields of compounds **10** were calculated for 2 steps.
