KETALISED ALPHA-LITHIATED AND BETA-LITHIATED ALPHA,BETA-UNSATURATED KETONES - NEW MASKED ACYLVINYL ANION EQUIVALENTS

The reaction of chloroketals 1, 5 and 10 with an excess of lithium pow der and a catalytic amount of DTBB (4-5%) in THF at -78 or -90 degrees C leads to the corresponding functionalised organolithium compounds 2 , 6 and 11, respectively, resulting from a chlorine/lithium exchange; treatment of these intermediates with different electrophiles [H2O, D2 O, Me(3)SiCl, Bu(t)CHO, PhCHO, Me(2)CO, (CH2)(4)CO, (CH2)(5)CO, PhCOMe ] affords, after hydrolysis with water, the corresponding products 3, 7 and 12, respectively. Careful acidic hydrolysis of these ketalised p roducts with a 10% aqueous solution of oxalic acid leads to the expect ed ketones 4, 9 and 13, respectively. (C) 1997 Elsevier Science Ltd.