Proton-carbon-13 coupling constants in carbocations. 6. Generation and trapping of the (1a.alpha.,7a.alpha.)-1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalen-2-yl cation

Abstract

New synthetic routes to (1aα,2β,7bα)-1a,2,3,7b-tetrahydro-1H-cyclopropa [a] naphthalen-2-ol (4b) and (1aα,2α,7aα)-1a,2,7,7a-tetrahydro-1H-cyclopropa [b] naphthalen-2-ol (6b) have been established involving dichlorocarbene addition to the appropriate dihydronaphthalene as the key step. Ionization of either alcohol 4b or 6b in FSO 3 H/SO 2 ClF at −130 o C produces the title cation 5b, in which the positive charge is stabilized by the adjacent benzo and cyclopropyl moieties. This is the same cation as that obtained previously by protonation of 1,6-methano [10] annulene (1). Generation of the cation 5b by protonation of C11- 13 C-enriched 1 has shown that the C11 bridge methylene carbon is incorporated into both benzylic positions (C2 and C7) and not the apical cyclopropyl carbon (C1). Application of the ΔJ equation shows that 5b adopts an anti-boat conformation in this superacid medium