3-Methylenetetrahydrofuran

Chan and Li reported that conjugated 1,3-butadienes were produced in moderate yields when carbonyl compounds reacted with 1,3-dichloropropene and zinc in water (Eq. 8.29).61 The use of 3-iodo-1-chloropropene instead of 1,3-dichloropropene greatly improved the yields. When the reactions were interrupted after their initial allyla-tions, subsequent base treatment of the intermediate compounds produced vinyloxiranes in high yields. Similarly, reactions of carbonyl compounds with 3-iodo-2-chloromethyl-l-propene followed by base treatment produced 2-methylenetetrahydrofurans (Eq. 8.30).62 Thus, the 3-iodo-2-chloromethyl-l-propene served as a novel trimethylene-methane equivalent.63... 

Pentyn-l-ol has been prepared from 4-penten-l-ol3 by bromi-nation followed by dehydrobromination with alkali,7 by the reaction of 3-bromodihydropyran with w-butylsodium or w-butyl-lithium,6 8 by the reaction of 2-methylenetetrahydrofuran with w-amylsodium or w-butyllithium,8 and by the method used in this preparation.9... 

Dihydrofurans are known to polymerize readily by cationic means but not by free radical initiation (77MI11102). 2,3-Dihydro-5-methylfuran (40), for example, has been polymerized to a stereoregular, optically active polymer (Scheme 9) by the appropriate choice of a catalyst system. Interestingly, the double bond isomer 2-methylenetetrahydrofuran (41) can be cationically polymerized (74CL499) to the isomeric polymer (42 Scheme 10). Under the polymerization conditions, no isomerization of (41) to (40) occurred, and the resultant polymer was shown to be isotactic and crystalline by NMR and X-ray analysis, respectively. 

Amongst the plant neolignans one finds some 2-methylenetetrahydrofurans of which burchellin (146) (lignan numbering) is an example. In this series the structures, stereochemistry and absolute configurations have been established by a combination of... 

BINAP-Ru complexes can catalyze the enantioselective hydrogenation of alkenyl ethers as shown in Scheme 1.15 [93], 2-Methyltetrahydrofuran with 91% ee and 87% ee can be synthesized by BINAP-Ru-catalyzed hydrogenation of 2-methylenetetrahydrofuran and the endo-type substrate, 2-methyl-3,4-dihydrofuran, in CH2C12 under 100 atm of hydrogen, respectively. With the same Ru complex, phenyl 1-phenylethyl ether, an acyclic alkenyl ether, is reduced in a moderate optical yield. 

The 2-methylenetetrahydrofuran depicted in the following scheme underwent a Claisen rearrangement catalyzed by -Bu,Al to provide an inseparable mixture of cycloheptenes as well as a ring-opened product <02T10189>. 

Rearrangement. A remarkable transformation by catalytic amounts of MeLi on an allylic alcohol which contains a silylalkyne moiety is the result of a Claisen rearrangement of a 2-methylenetetrahydrofuran intermediate. 

Kve interesting results, the study was extended to the carbon ana-g, the cyclic vinyl etters. Thus, 2-methylenetetrahydrofuran (XIX) when treated with di-tert-butyl peroxide at 120 C ve a polymer, in which only about 5% of the rings had oraned (19). Af rently the ketone group is sufficiently less stable than me... 

Cyclization. On treatment with La[N(SiMe3)2]3, a 4-alkynol forms the alkoxide which cyclizes to give 2-methylenetetrahydrofuran the isomer with endocyclic double bond is also formed from 3,4-pentadienol. A modified trisfhexamethyldisilazide) of lanthanum (and of several other rare earth metals) (1) catalyzes intramolecular hydroamina-tion of alkynylamines and the products also undergo hydrosilylation. ... 

An 0-alkylation procedure generated 2-methylenetetrahydrofuran skeletons in good yields, and an example is shown in the following scheme <043006715>. 

Methylenetetrahydrofurans. 4-Alkynols cyclize on exposure to silver carbonate. An oxygen functionality at the propargylic position has a remarkable accelerating effect. 

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