A simple and efficient procedure for carbon-carbon bond formation has been developed starting from alcohols and active methylene-containing compounds using silica gel supported sodium hydrogen sulfate (NaHSO 4 /SiO 2 ) under mild conditions. NaHSO 4 /SiO 2 can be reused without loss of catalytic activity at least ten times.

GeneralMelting points were determined on Büchi Melting Point B-540. NMR spectra were recorded on a JEOL ECX 400 spectrometer. Tetramethylsilane ( = 0) was used as an internal standard for 1 H NMR and CDCl 3 ( = 77.0) for 13 C NMR. Mass analysis were performed on a Agilent G1969 LC/MDS TOF. IR spectra were recorded on a NICOLET 380 FT-IR. Elemental analyses were performed on a J Science Lab. micro corder JM-10. Preparation of NaHSO 4 /SiO 2SiO 2 [Wakogel C-200 (Wako Pure Chemical Ind. Ltd.), 10 g] was added to a solution of NaHSO 4 ·H 2 O (30 mmol, 4.14 g) in distilled water, and the mixture was stirred at room temperature for 0.5 h. The water was removed by rotary evaporator under reduced pressure, and the resulting reagent was dried in vacuo (10 mmHg) at 120 °C for 5 h. Typical procedureA mixture of -diketones 1 (6 mmol), o-hydroxybenzyl alcohols 2 (2 mmol) and NaHSO 4 /SiO 2 (2.1 mmol, 1.0 g) in dichloroethane (10 mL) was stirred at 80 °C for 5 h, and then the used supported reagent was removed by filtration. The filtrate was evaporated to leave crude product, which was purified by column chromatography (hexane/ethyl acetate) to obtain 3.

Application of 1,3-di-tert-butylpentan-1,3-dione as the diketone or 2-(hydroxy-tert-butyl-methyl)phenol as the o-hydroxybenzylic alcohol fails to give the desired chromenes. -(AOYAMA*, T.; YAMAMOTO, T.; MIYOTA, S.; HAYAKAWA, M.; TAKIDO, T.; KODOMARI, M.; Synlett 25 (2014) 11, 1571-1576, http://dx.

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