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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)

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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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Carbon-13 nuclear magnetic resonance (13C NMR) has been used rather extensively in the characterization of ethylene-propylene copolymers and terpolymers. Chemical shift assignments on these copolymers were first made by Carman and revised only slightly by him recently. Despite all the work that has been done to assign the lines in the 13C NMR spectrum to the various sequence structures in ethylene-propylene copolymers, ambiguity still remains in some of the assignments, such as the assignment of the Sαβ line. It still is not known whether it is attributable entirely to two propylenes with one of them inverted, to an ethylene sandwiched between two propylenes with one of them inverted, or to an equal population distribution of these two structures. Carman and coworkers state that inversion of propylene in their copolymers is certain, but because of the large error in the calculation, the degree of inversion can be between 10 and 40% of the propylene content. His suggestion is that the Sαβ line is attributable to a combination of the two structure forms indicated above. Tanaka6 also makes this same suggestion in his 13C NMR work. He based his conclusion on some earlier infrared work. Most recently Randall describes a sequence length distribution method in which he estimates that the total amount of propylene inversions is the order of 20–30% for a concentration range of about 50–60 wt% propylene in copolymers with ethylene. Ray does not have to deal with the problem, as his 13C NMR spectra show no evidence of propylene inversions. His copolymers were prepared with an aluminum-titanium catalyst. Ours as well as Carman's were prepared with an aluminum-vanadium catalyst. Our reason for undertaking this program was to aid in the assignment of the Sαβ line. For this effort we prepared a series of ethylene-propylene copolymers that are carbon-13 enriched in both carbons of the ethylene, and we analyzed them by 13C NMR.