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8. A. J. Birch and I. D. Jenkins, Tetrahedron Lett., 119 (1975).
3,5,5-TRIMETHYL-2-(2-OXOPROPYL)-2-CYCLOHEXEN-l-ONE [2-Cyclohexen-l-one, 3,5,5-trimethyl-2- (2-oxopropyI)-]
CH3 H3C XOCCH3
H,C H3C CH3
H3C H3C CH3
H3c H3c CH3
CeCNH^NOak acetonitrile, water, reflux
Submitted by Z. Valent a1 and H. J. Lnr3
Checked by Ò. H. O’Neim,, W. Thompson, D. H. Hawke,
and R. E. Ibkland
r 1. Procedure
The apparatus used for the photocycloaddition reaction is shown in Figure 1. In the reaction vessel is placed a solution of 34.5 g. (0.25 mole) of 3,5,5-trimethyl-2-cyclohexen-l-one (isophorone) (Note 1) and 500 g. (5 moles) (Note 2) of isopropenyl acetate (Note 3) in 625 ml. of benzene. A constant and moderate flow of argon (Note 4) is maintained to agitate the solution throughout the reaction period. The trap is filled with isopropyl alcohol-dry ice (Note 5). The solution is irradiated with a 450-watt Hanovia high-pressure quartz mercury vapor lamp using a Pyrex filter for 96 hours (Note 6). Concentration of the resultant solution under reduced pressure (water aspirator) gives 65-80 g. of crude 7-acetoxy-4,4,6,7-tetramethylbicyclo[4.2.0]octan-2-one (Note 7).
Figure 1. Ë, Dewar flask; Â, sintered glass filter; Ñ, metal cooling coil; D, water inlet; E, water outlet; F, reaction vessel; Q, quartz immersion well; H, pyrex filter; I, lamp; J.> nitrogen gas inlet; K, ground glass joint; L, condenser; M, calcium chloride drying tube.
The preceding crude photo-adduct without purification is dissolved in 250 ml. of methanol and transferred to a 1-1., three-necked, round-bottomed flask fitted with overhead stirrer with Teflon blade, addition funnel, and argon inlet. The solution is cooled with an ice bath and 500 ml. of 4 M aqueous sodium hydroxide is added over a period of 20 minutes with stirring. Upon completion of the addition, the ice bath is removed and stirring is continued for 16 hours. The brown solution is then extracted with four 500-ml. portions of chloroform. The organic extract is washed with saturated sodium chloride solution, dried over magnesium sulfate, filtered, and concentrated under reduced pressure. Distillation of the residue through a 6-cm. Vigreux column affords, after a small forerun, 23.0-27.9 g. (47-57%) of 7-hydroxy-4,4,6,7-tetra-methylbicyclo[4.2.0]octan-2-one (Note 8) collected at 92-101° (0.2 mm.).
A 2-1., three-necked, round-bottomed flask, fitted with an overhead stirrer with Teflon blade, a Fries condenser, and a stopper, is charged with a solution of 9.8 g. (0.05 mole) of 7-hydroxy-4,4,6,7-tetramethyI-bicyclo[4.2.0]octan-2-one in 600 ml. of 50% (by volume) aqueous acetonitrile and 82 g. (0.15 mole) (Note 9) of eerie ammonium nitrate (Note 10) is added in one portion with stirring. Immediately after completion of the addition, the flask is immersed in an oil bath preheated to 170°. Befluxing occurs in about 10 minutes and is continued for 5 minutes. During this period the color of the solution changes from light brown to pale yellow. At the end of this time the reaction mixture is immediately poured onto crushed ice and extracted with four 600-ml. portions of chloroform. The combined extracts are washed with saturated sodium hydrogen carbonate and then saturated sodium chloride, dried over magnesium sulfate, and filtered. The solvent is removed under reduced pressure and the residue distilled, using a short-path distillation apparatus. All material boiling at 70-100° (0.25 mm.) is collected. Fractionation of the yellow oil through a 6-cm. Vigreux column gives 4.68-4.71 g. (48-50%) of 3,5,5-trimethyl-2-(2-oxopropyl)-
2-cyclohexene-l-one, b.p. 81—85° (0.4 mm.) (Note 11).
1. Isophorone obtained from M Ñ and Â Manufacturing Chemists was freshly distilled, b.p. 73° (4.5 mm.).
2. In order to minimize the formation of cyclohexenone dimer and to
achieve cleaner photo-adduct, it is essential to use a large excess of olefin in the photocycloaddition of a cyclohexenone to an olefin.3
3. Supplied by Aldrich Chemical Company, Inc.
4. Submitters used nitrogen purified by passing it through a set of gas wash bottles containing Fieser’s solution,4 concentrated sulfuric acid, sodium hydroxide, and calcium chloride.
5. The submitters filled the Dewar flask with ice and water. After
2 hours the ice had melted and water was left in the flask for cooling.
6. The progress of the reaction was monitored by injecting after each 24-hour period an aliquot into a gas chromatograph and checking the peak corresponding to isophorone. Alternatively, thin-layer chromatography (E. Merck 0.25-mm. silica gel plates developed with ethyl acetate) can be used.