Study of the reaction mechanism of cyclization with the aid of deuterium Communication 2

Summary

• 1. Deutero-2,4,-dimethyl- Δ² -cyclopenten-1-one was obtained by the cyclization of 2-methylhexadien-3-one in the presence of deuterium enriched phosphoric acid.

• 2. When deutero-2,4-dimethyl- Δ² -cyclopenten-1-one was ozonized, methylsuccinic acid was obtained which contained almost all the initial deuterium of the dimethylcyclopentenone. This excludes the presence of deuterium at carbon atoms 1,2,3 or 6 in the molecule of deutero-2,4-dimethyl- Δ²-cyclopenten-1-one.

• 3. Oxidation of deutero-2,4-dimethyl- Δ² -cyclopenten-1-one with seleniumdioxide gave 2,4-dimethyl-cyclopenten-1,5-dione containing no deuterium. From this it follows that the deuterium in deutero-2,4-dimethyl Δ² -cyclopenten-1-one occurs at carbon 5, i.e., at the methylene group adjacent to the carbonyl.

• 4. This position nf deuterium in deutero-2,4-dimethyl- Δ²-cyclopontenone shows that it is not isopropenylallyl-ketone (2-methyl-1,5-hexadien-3-one) (I) but its isomer, 2-methyl-1,4-hexadien-3-one (IV) that is cyclized.