The preparation of ethyl
4-ethoxy-2-methylcyclohexa-1,3-diene-1-carboxyate, ethyl 4-isopropoxy-
2-methylcyclohexa-1,3-diene-1-carboxylate, t-butyl
4-isopropoxy-2-methylcyclohexa-1,3-diene-1- carboxylate, ethyl 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate,
and t-butyI 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate
from Hagemann's ester and its t-butyl analogue in the presence of diethyl or diisopropyl sulfates and sodium hydride in dimethyl
sulfoxide, or pivaloyl chloride and N,N,N',N'-tetramethylethylenediamine
in tetrahydrofuran is described. The foregoing dienol ethers and esters are
smoothly deprotonated by lithium diisopropyl-
amide in tetrahydrofuran at -78" to give the corresponding ester dienolates, which react regio- specifically with a number
of electrophiles, either a or y to the alkoxycarbonyl group of the dienol ether or ester. A number
of the products, which are generally obtained in good yields, have been hydrolysed to Hagemann's ester derivatives substituted
exclusively at C1.
The cyclization of compounds obtained from ethyl dienol ether and dienyl pivalate derivatives of Hagemann's ester has been examined. The carbanions of methyl phenyl sulfone and methyl phenyl sulfoxide react with the methylated dienol ether (4) to give the β-keto sulfone (8) and sulfoxide (9), the former of which was converted into the oxabicyclo[4.3.0]non-1-en-3-one (16). The iodide (17) with potassium t-butoxide in t-butyl alcohol gave the octahydronaphthalenone (18). With lithium ethoxide in tetrahydrofuran the octahydronaphthalenedione (22) was obtained from the dienyl pivalate (24). Both reactions involve the generation and intramolecular cyclization of a dienolate produced by cleavage of the pivaloyl group in each of (17) and (24). The scope and limitations of these reactions are briefly discussed.
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