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Organic Synthess - Johnson S.K.

Johnson S.K., Brossi A., Seebach D. Organic Synthess - Michigan, 1977. - 138 p.
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7. This crude product is contaminated mainly by polymeric compounds. An attempted distillation of this material was unsuccessful; partial decomposition occurred at 110-125 (0.3 mm.). If it is desirable, purification can be achieved by extensive silica gel column chromatography with 5% ether in benzene.
8. The product is a mixture of at least two diasteriomers as indicated by its proton magnetic resonance spectrum (carbon tetrachloride) showing eight singlets at S 0.9-1.22 for a total of twelve methyl protons. Its ir spectrum (neat) exhibits absorption bands at 3440 and 1695 cm.-1. A molecular ion peak at 196.1447 (calcd. for C12H20O2:196.1463) is displayed in its mass spectrum.
9. Use of less of the reagent resulted in partial recovery of the starting material.
10. Procured from Fisher Scientific Company.
11. Infrared (neat) cm.-1: 1720, 1670, 1645; proton magnetic resonance (chloroform-rf) 8: 1.03, 1.87, 2.13, 2.20, 2.25, 3.43 (all singlets); mass spectrum m/e 194.1299 (M+).
3. Discussion
In recent years the application of photocycloaddition reactions to organic synthesis has been growing in importance.6,6 The procedure described is illustrative of a general method3 based on a photocyclo-addition reaction for the introduction of an activated alkyl group specifically to the a-carbon atom of an a,/3-unsaturated cyclohexenone. Especially significant is the fact that the method is also applicable to
,/S-unsaturated cyclohexenones which do not possess any enolizable y-hydrogen atom and thus to which normal alkylation reactions7 cannot be applied. A closely related procedure involving the photocycloaddition of vinyl acetate to 2-cyclohexenones (in which enolization toward the 6-position is forbidden) followed by bromination and fragmentation of the adduct has been reported.3,8 It has also been observed9 that photo-adducts of cycloalkenones and vinylene carbonate undergo fragmentation upon alkali treatment giving 2-(2-oxoethyl)-2-cycloalken-l-ones.
1. Department of Chemistry, University of New Brunswick, Fredericton, N.B., Canada.
2. Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada.
3. N. R. Hunter, G. A. MacAlpine, H. J. Liu, and Z. Valenta, Can. J. Chem., 48, 1436 (1970).
4. L. F. Fieser, J. Amer. Chem. Soc., 46, 2639 (1924).
5. References cited in Ref. 3.
. For reviews, see P. E. Eaton, Accounts Chem. Res., 1, 60 (1968); P. de Mayo, Accounts Chem. Bes., 4, 41 (1971); P. G. Bauslaugh, Synthesis, 287 (1970).
7. H. O. House, Modem Synthetic Reactions, 2nd ed, W. A. Benjamin, Inc., Menlo
Park, Calif., Chap. 9. _
8. H. J. Liu, Z. Valenta, J. S. Wilson, and . T. J. Yu, Can. J. Chem., 47, 609 (1969).
9. P.-T. Ho, S. F. Lee, D. Chang, and K. Wiesner, Experientia, 27, 1377 (1971).
TR0P0L0NE [2,4,6-Cycloheptatrien-1-one, 2-hydroxy-]
Submitted by Richabd A. Minns1 Checked by Arthur J. and William A. Sheppard
1. Procedure
A. r7,l-Dichlor6bicyclo\b.2.(f\hept-2-en-&-one. In a 2-1., three-necked, round-bottomed flask fitted with an addition funnel, a reflux condenser, and a mechanical stirrer are placed 100 g. (0.68 mole) of dichloroacetyl chloride (Note 1), 170 ml. of cyclopentadiene (2 moles) (Note 2), and 700 ml. of pentane (Note 3). The solution is heated to reflux under nitrogen and rapidly stirred while a solution of 70.8 g. (0.70 mole) of triethylamine (Note 4) in 300 ml. of pentane is added over a period of 4 hours (Note 5). After the cream-colored mixture has been refluxed for an additional 2 hours, 250 ml. of distilled water is added to dissolve the triethylamine hydrochloride; the layers are separated in a 2-1. separatory funnel. After extraction of the aqueous layer with two 100-ml. portions of pentane, the combined organic layers are filtered and dried by passage through absorbent cotton. Pentane and excess cyclopentadiene are then removed by rapid distillation. The resulting viscous, orange liquid is fractionally distilled under reduced pressure through a 30-cm. Vigreux column. Heat is supplied from an oil bath held at 105. During collection of the first fraction, which consists mainly of dicyclopentadiene (Note 6), b.p. 61-62 (9 mm.), the cold finger and take-off tube must be warmed periodically with a heat gun to prevent plugging. The 7,7-dichloro-bicyclo[3.2.0]hept-2-en-6-one, 101102 g. (84-85%), is collected as a colorless liquid, b.p. 66-68 (2 mm.), n25d 1.5129, having a purity > 99% as determined by gas chromatographic analysis (Notes 6, 7).
B. Tropolone. In a 1-1., three-necked, round-bottomed flask equipped with a mechanical stirrer, addition funnel, and reflux condenser are placed 500 ml. of glacial acetic acid and then, cautiously, 100 g. of sodium hydroxide pellets. After the pellets have dissolved, 100 g. of 7,7-dichlorobicyclo[3.2.0]hept-2-en-6-one is added and the solution is maintained at reflux under nitrogen for 8 hours. Concentrated hydrochloric acid is then added until the mixture is about pH 1; approximately 125 ml. of acid is required. After the addition of 11. of benzene, the mixture is filtered and the solid sodium chloride is washed with three 100-ml. portions of benzene. The two phases of the filtrate are separated and the aqueous phase is transferred to a 1-1. continuous extractor (Note 8) which is stirred magnetically. The combined benzene phase is transferred to a 2-1. pot connected to the extractor and the aqueous phase is extracted for 13 hours. Following distillation of the benzene, the remaining orange liquid is distilled under reduced pressure
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