DTBB-catalysed lithiation of 1,7-dihydrodibenzothiepin

Treatment of 1,7-dihydrodibenzothiepin (1) with an excess of lithium powder and a catalytic amount of DTBB (5 mol%) at −78°C for 30 min followed by reaction with a carbonyl compound {tBuCHO, Ph(CH2)2CHO, PhCHO, Me2CO, [Me(CH2)4]2CO, (CH2)5CO, (CH2)7CO, (−)-menthone} at the same temperature led, after hydrolysis with 3N hydrochloric acid, to sulfenyl alcohols 4. When alkoxide 3, which is formed after addition of the first carbonyl compound [Me2CO, (CH2)5CO, (−)-menthone], is stirred at room temperature for 30 min, a new lithiation occurred and after addition of a second electrophile [Me2CO, Et2CO, (CH2)5CO, ClCO2Et] and final hydrolysis with water, difunctionalised biphenyls 6 are formed. Treatment of the sulfenyl alcohol 4c with 85% phosphoric acid in toluene at reflux for 4 h gave the sulfur-containing eight-membered heterocycle 8c in good yield.