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 degreesC for 30 min followed by reaction with a carbonyl compound {' BuCHO, Ph(CH2)(2)CHO, PhCHO, Me2CO, [Me(CH2)(4)](2)CO, (CH2)(5)CO, (CH2)(7)CO, (-)-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 [Me,CO, (CH,),CO, (-)-menthone], is stirred at room temperature for 30 min, a new lithiation occurred and after addition of a second electrophile [Me2CO, Et2CO, (CH2)(5)CO, 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. (C) 2001 Elsevier Science Ltd. All rights reserved.