On the Isolation of (+)3-Thujone

Abstract

Conditions necessary for the formation of the (+)3-thujone bisulfite adduct 1a and its utilization for the isolation of pure (+)-thujone have been established.

The chemistry of terpenes. Part 27. The halogenation of (+)-thujone and of (–)-carvotanacetone, and the stereochemistry and mechanism of formation of ‘tribromothujone’

“…Brominution of ( -)-4-Chlorothujone (9): ( -)-( 1 S,2S,4R,5S)-2-Bromo-4-chlorothujan-3-one (12) and ( -)-( 1 S,2R,4R,5S)-2-Bromo-4-chlorothujan-3-one (13).-Bromine (6.15 g, 0.95 mol equiv.) in carbon tetrachloride (1 5 ml) was added during 40 min to a stirred solution of (-)-4-chlorothujone (7.6 g) in carbon tetrachloride (30 ml).…”

“…Early fractions gave ( -)-( 1S,2R,4R,5S)-2-bromo-4-chlorothujan-3-one (13) (2.8 g), which after a second run through a column was obtained as a liquid, [a]Dz2 -262" ( c 0.74); vmaX,(L) 3 520, 1 774, 775, and 655 cm-' ; 6,O. 38 ( 1 H, dd, J 7,4 Hz, ~x -H ) , Equilibration of ( -)-( 1 S,2S,4R,5S)-2-Bromo-4-chlorothujan-2one (12) with its 3-Epimer (13).-A mixture of the bromo chloro ketone (12) (0.4 g), finely powdered pyridinium bromide (1 g) and dimethyl sulphoxide (2 ml) was stirred at room temperature for 60 h. Work-up gave a pale brown oil (0.4 g), [%IDzo -195" (c 3.4); vmax,(L) 1 770 cm-'. Its 'H n.m.r.…”

“…Reactions of Zinc Bromide with the Bromochlorothujones (12) and (13).-(a) ( -)-(5R,6R)-5,6-Dibromo-5-isopropyl-2-methylcq'clohex-2-enone (24) from (12). A mixture of (-)-(1 S,2S,4R,5S)-2-bromo-4-chlorothujone (12) (2.0 g), anhydrous zinc bromide (1.5 g), and dry ether (25 ml) was stirred under reflux for 40 h and then at room temperature for 100 h: Starting material had then been consumed.…”

“…16 : 7 proportions. Rapid chromatography on silica gave the dibromo compound (24) as a liquid, [x]D22 -7.0' (c. 1.3) (b) ( + )-( 5R,6S)-5,6-Dibromo-5-isopropyl-2-methylcqlclo~e~-2-enone (25) ,from (13). A mixture of ( -)-(I S,2 R,4R,5S)-2bromochlorothujone (13) (0.6 g), anhydrous zinc bromide (3 g), and ether (25 ml) was gently refluxed, and stirred for 5 h. Workup gave a syrup which partially solidified at -10 "C. The solid (0.1 g) was first pressed on a porous plate and then recrystallised from aqueous methanol to give ( + )-(5R,6S)-5,6-dibromo-5-isopropy1-2-methylcyclohex-2-enone (25) as needles, m.p.…”

“…Reaction of Bromine with ( -)-( 1 S72R,4R,5S)-2-Bromo-4chlorothujan-3-one (13) in Light: (lS,2R,4R,5S)2,7-Dibromo-4chlorothujun-3-one (20).-A solution of the bromo chloro compound (13) in CDCl, (11.5 mg in 1.2 ml) (0.6 ml) was treated with 0.056 ml of a solution of bromine (0.4 ml) in carbon tetrachloride (10 ml) and the solution was kept in the dark for 24 h. Intermittent examination by 'H n.m.r. spectroscopy showed that no reaction had taken place.…”