Chemical Transformation of Terpenoids. IV. Acid Treatment of (3R)-1-Vinyl-, (3R)-1-Hydroxypropenyl-, and (3R)-1-Epoxyethyl-5-methoxy-1, 2, 2-trimethylcyclopentane Derivatives : Ring Enlargement Reactions and Successive Migrations of Methyl Residues

抄録

Three 5-methoxy-1, 2, 2-trimethylcyclopentane derivatives, i.e., (+)-(1R, 3R, 5S)-3-acetoxymethyl-5-methoxy-1, 2, 2-trimethyl-1-vinylcyclopentane (3), (+)-(1R, 3R, 5S)-3-acetoxymethyl-1-(3'-hydroxypropenyl)-5-methoxy-1, 2, 2-trimethylcyclopentane (4), and (-)-(1R, 3R, 5S, 1'R)-3-acetoxymethyl-1-(1', 2'-epoxyethyl)-5-methoxy-1, 2, 2-trimethylcyclopentane (5), which were synthesized from d-camphor (1) via 5-oxo-d-bornyl acetate (2), were subjected to acid treatment. It was found that i) treatment of 3 with 2, 4, 4, 6-tetrabromocyclohexa-2, 5-dienone yielded a 4-bromo-2-oxabicyclo [3.3.0] octane derivative (8), ii) BF₃-etherate treatment of 4 resulted in a ring-enlargement reaction giving two cyclohexane derivatives (13, 14), and iii) BF₃-etherate treatment of 5 furnished a 2-oxabicyclo [3.3.0] octane derivative (15) which was derivable through successive migrations of the methyl residues.