Reaction of 18 beta,19 beta-epoxylupan-21-one derivatives with acids: A way to 21,22-disubstituted lup-18-ene triterpenoids

Depending on the conditions and the acid employed, 18 beta,19 beta-epoxy-28 -hydroxy 21-oxolupan-3 beta-yl acetate (2a) and 18 beta,19 beta-epoxy-21-ox oIupane-3 beta,28-diyl diacetate (2b) on treatment with acid gave three typ es of products: (i) 28-nor derivatives: 21-oxo28-norlupa-16,18-dien-3 beta- yl acetate (6), 19 beta-hydroxy-21-oxo-28-norlup-17-en-3 beta-yl acetate (7 ) and 17 xi-hydroxy-21 -oxo-28-norlup-18-en-3 beta-yl acetate (8), (ii) lup a-12, 18-dien-21-ones 4a and 4b, and (iii) 22 beta-substituted lup-18-en-21 -one derivatives of the type 5. The formation of 22 beta-substituted deriva tives of the type 5 probably proceeds in the enol form of epoxy ketone 2. O pening of the epoxide ring with shift of the double bond to position 19(21) and attack by nucleophilic species at C-22 followed by elimination of wate r and re-formation of the 22-oxo group leads to derivatives of the type 5.