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2005
Terpenes
U 0200
01- 159
Thermal Isomerization of Isoborneols and Dehydroisoborneols to New Chiral
Building Blocks in Terpenoids Synthesis. — Substituted isoborneols (I) and (VII)
and dehydroisoborneol (X) are thermally isomerized in a flow reactor system under
DGPTI (dynamic gas-phase thermo-isomerization) conditions at temperatures between
480 and 630°C. In all cases, the isomerization proceeds highly regio- and stereoselective affording the enantiomerically pure monocyclic carbonyl compounds (II) and (XI)
in good yields, respectively. The concept of the "cleavage of the weakest single bond"
is confirmed. In contrast, DGPTI of the vinyl substrate (VII) allows concerted retro-ene
and oxy-Cope rearrangements. In addition, a new route to trans-α-campholanic acid
(IV) and trans-α-dihydrocampholytic acid is presented by regioselective Baeyer—Villiger oxidation and subsequent hydrolysis of (IIb) and (IIc). — (RUEEDI*, G.;
HANSEN, H.-J.; Helv. Chim. Acta 87 (2004) 8, 1968-1989; Org.-Chem. Inst., Univ.
Zuerich, CH-8057 Zuerich, Switz.; Eng.) — Bartels
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