ChemInform Abstract: Transformations of Bicyclo(4.3.0)non‐3‐enyl Carbocation Having Charge at Atom C‐7.

Abstract

Transformations of Bicyclo(4.3.0)non-3-enyl Carbocation HavingCharge at Atom C-7. -It is found that the title carbocation, which can be generated by dehydration of the alcohol (II) or solvolysis of the tosylate (IV), does not undergo transannular cyclization like its analogue having the charge at C-3. It is transformed into the bicyclo(4.3.0)nonadienes ( III), (V) and (VI). -(NIGMATOVA, V. B.; ZAITSEV, YU. V.; ANFILOGOVA, S. N.; PEKHK, T. I.; BELIKOVA, N. A.; Zh. Org. Khim. 30 (1994) 5, 686-691; Moskovskii gos. univ. im. Lomnosova, Moskva, Russia; RU)

Synthesis of oxa-bridged derivatives from Diels–Alder bis-adducts of butadiene and 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene

“…The reaction mixture was purified by silica gel chromatography to afford the mono-adduct 4 in 7% yield as an inseparable mixture of endo and exo isomers [16] ( endo : exo = 90:10, as determined by 1 H NMR spectroscopy) and the two diastereomeric bis-adducts 5 and 6 as a 1:1 mixture in 92% yield (Scheme 2). …”

“…For the preparation of the 2:1 adducts, 2 equivalents of 1,2,3,4-tetrachlorodimethoxycyclopentadiene 1a and one equivalent of 3-sulfolene were heated at 140–150 °C for 69 h in a sealed tube. The reaction mixture was purified by silica gel chromatography to afford the mono-adduct 4 in 7% yield as an inseparable mixture of endo and exo isomers [ 16 ] ( endo : exo = 90:10, as determined by 1 H NMR spectroscopy) and the two diastereomeric bis-adducts 5 and 6 as a 1:1 mixture in 92% yield ( Scheme 2 ).…”

“…The bis-adduct obtained from 1a and gaseous 1,3-butadiene was previously assigned as “ endo , exo -bis(7,7-dimethoxy-1,2,3,4-tetrachloronorborn-2-en-5-yl)” [16]. In our reinvestigation we used 3-sulfolene as a 1,3-butadiene source to prepare both the mono- and bis-adducts.…”

“…We were interested in exploring the previously overlooked stereochemical outcome of the Diels–Alder reaction between 1a and 1,3-butadiene [ 15 – 16 ]. The bis-adduct obtained from 1a and gaseous 1,3-butadiene was previously assigned as “ endo , exo -bis(7,7-dimethoxy-1,2,3,4-tetrachloronorborn-2-en-5-yl)” [ 16 ]. In our reinvestigation we used 3-sulfolene as a 1,3-butadiene source to prepare both the mono- and bis-adducts.…”