Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Synthetic Studies of α-Tocopherol. II. Synthesis of Trimethyl-benzoquinone
Takehiko IchikawaHiroko OwatariTetsuya Kato
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1968 Volume 41 Issue 5 Pages 1228-1232


Trimethylbenzoquinone (XII), a raw material for the synthesis of trimethylhydroquinone (XIII), was synthesized from trimethylcyclohexenones and trimethylcyclohexene by oxidation. Ethyl α-propionylpropionate (II) prepared from ethyl propionate was condensed with methyl vinyl ketone to yield 4-methyl-4-ethoxycarbonylocta-3,7-dione (IV), which was then dehydrated with beryllium chloride to give 2,3,6-trimethyl-6-ethoxycarbonyl-2-cyclohexen-1-one (V). The product (V) was heated with alkali to give 2,3,6-trimethyl-2-cyclohexen-1-one (VI). The refluxing of a solution of IV in a mixture of acetic acid and hydrochloric acid also gave rise to VI. When II was condensed with crotonaldehyde, 2,5,6-trimethyl-2-cyclohexen-1-one (VIII) was obtained in a single step. 1,4(or 1,5)-Dimethyl-5-(or 4)-formyl-1-cyclohexene (IX), obtained by the Diels-Alder reaction of crotonaldehyde with isoprene, was reduced by hydrazine hydrate to give 1,4,5-trimethyl-1-cyclohexene (X). X was oxidized with t-butyl chromate and acetic anhydride to give 3,5,6-trimethyl-2-cyclohexen-1-one (XI). VI, VIII, XI, and X were oxidized with t-butyl chromate and acetic anhydride to give XII in 53, 52, 22, and 12% yields respectively. The oxidation of VIII by selenium dioxide gave XII in a 23% yield, but only a trace of XII was formed by the similar oxidation of X.

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