A convenient synthesis of 3-methyl-2,3-dihydrofuran and 4-methyl-3,4-dihydro-2H-pyran from readily available starting materials has been achieved. The application of these cyclic ethers to the synthesis of compounds containing isoprene units as part of their structure is discussed.The hydroformylation of methallyl acetate results in the formation of y-acetoxy-8-methylbutyraldehyde. The structure of this compound was established by oxidation and by its conversion to 2-alkoxy-4-methyltetrahydrofuran. The pyrolysis of 2-alkoxy-4-methyltetrahydrofuran results in the formation of 3-methyl-2,3-dihydrofuran.The condensation of crotonaldehyde with vinyl n-butyl ether results in the formation of 2-n-butoxy-4-methyl-3,4-dihydro-2H-pyran, which yields 4-methyl-3,4-dihydro-2H-pyran upon reduction and dealkoxylation.The present work was initiated with the object of developing an expedient synthesis for the hitherto unknown 3-alkyl-2,3-dihydrofurans and 4-alkyl-3,4-dihydro-2H-pyrans. Our interest in these cyclic vinyl ethers stems from their possible application as intermediates for the synthesis of compounds which contain one or more isoprene units as part of their structure. As shown in the accompanying flow sheet, an extension of the olefin synthesis previously described starting with dihydropyran2 to 3-methyl-2,3-dihydrofuran (I)
The literature on reactions of carbon monoxide with thiols is limited to those in which either acety-lene1 or an olefin2 is present as a third component. The products are the thiol esters of the carbonylated unsaturate. There are no accounts of the direct reaction of carbon monoxide with thiols or their derivatives.We now wish to report that carbon monoxide reacts with thiols, disulfides, and sulfides to give thiol esters in accordance with Equations 1-3 in the presence of a cobalt carbonyl catalyst or certain metal oxide catalysts at 250-300°and 100-1000 atm. Results are summarized in Table I.
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