Ether, methyl propenyl

Carbenium ions are sp2 hybridized with the empty orbital perpendicular to the plane containing the three substituents. Calculations confirm both the flat structure of carbenium ions and the shorter linkage with aryl substituents due to the partial double-bond character. As discussed previously, the positive charge is not localized just on the sp2-hybridized carbon of the carbenium ion, but is dispersed onto neighboring substituents. Table 1 presents the charge distribution in model carbenium ions formed by protonation of propene, isobutene, styrene, a-methylstyrene, methyl vinyl ether, and methyl propenyl ether. 

Acetals, however, are easily regioselectively introduced (Schemes 3.11 and 3.12) [9]. Benzylidene acetals are preferentially formed as six-membered dioxane-type acetals (i.e., hexopyranosides form 4,6-0-benzylidene derivatives), whereas isopropylidene acetals are more stable as five-membered dioxolane acetals formed on vicinal cw-diols. However, the selectivity is not complete and methyl mannoside, for example, produces mixtures of the mono- and di-acetal compounds. The use of methyl propenyl ether yields mainly the kinetic product (the 4,6-0-isopropylidene acetal). Complementary to these traditional acetals is a rather recently developed acetal — the BDA-acetal [21]. In contrast to other acetals, this exclusively forms acetals between... 

Alkyl enol ethers can be conveniently prepared by the alkylation of a-methoxyvinyllithium and related metallated enol ethers. In a typical example, methyl vinyl ether (1) is converted by r-butyllithium to give a-methoxyvinyllithium (2). Reaction of (2) with octyl iodide gives the enol ether (3). Metallation of methyl propenyl ether (4) and methyl allenyl ether (5) can be similarly executed. ... 

Ethyl vinyl ether Isobutyraldehyde Methyl propenyl ether 2 -Methylthiopropional-dehyde, 85 mm. 

The synthesis of crocetindialdehyde tetramethyl acetal, as the C2o-buUdmg block, follows the C5 + Cjo + C5 strategy. The required methoxyisoprene is accessible from acetaldehyde dimethyl acetal and methyl propenyl ether in a Lewis acid-mediated reaction. 

Cis- and trans-isomevs of methyl propenyl ether, structurally similar to 2-phenylvinyl methyl ether, also undergo equimolar copolymerization with Under the conditions of the study, i.e., benzene solvent, free-radical initiator, and 60°C polymerization temperature, the cw-isomer was shown to be the most reactive. The orders of the two monomers toward the MA radical (1/ri) were cis = 0.431 and trans = 0.347. The specific viscosities of the copolymers, measured in acetone at 30°C, varied from 0.11 to 0.42 dl/g. Alternating copolymers were obtained over a wide variation of monomer feed ratios. 

The addition of acetylene to acetone under Favorski-Babayan conditions gives meth-ylbutynol (43) which can be hydrogenated to methylbutenol (44) using a Lindlar catalyst [25-29]. When this is treated with methyl propenyl ether (the vinyl ether of acetone), trans-etherification takes place to give (45), which then undergoes a Claisen-Cope... 

Diethoxypropane passed at 340-350° through a vertical Pyrex tube packed with a catalyst prepared from heavy kaolin, Gooch asbestos, water glass, and water-methyl propenyl ether. Y 67.7% based on startg. m. consumed.— Alumina (cf. Synth. Meth. 11, 926) was unsuitable. M. F. Ansell and B. Gadsby, Soc. 1958, 3388. 

A disadvantage of the THP group is the fact that a new stereogenic center is produced at C(2) of the tetrahydropyran ring. This presents no difficulties if the alcohol is achiral, since a racemic mixture results. However, if the alcohol is chiral, the reaction gives a mixture of diastereomers, which may complicate purification and/or characterization. One way of avoiding this problem is to use methyl 2-propenyl ether in place of dihydropyran (abbreviated MOP, for methoxypropyl). No new chiral center... 

Some representative Claisen rearrangements are shown in Scheme 6.14. Entry 1 illustrates the application of the Claisen rearrangement in the introduction of a substituent at the junction of two six-membered rings. Introduction of a substituent at this type of position is frequently necessary in the synthesis of steroids and terpenes. In Entry 2, formation and rearrangement of a 2-propenyl ether leads to formation of a methyl ketone. Entry 3 illustrates the use of 3-methoxyisoprene to form the allylic ether. The rearrangement of this type of ether leads to introduction of isoprene structural units into the reaction product. Entry 4 involves an allylic ether prepared by O-alkylation of a (3-keto enolate. Entry 5 was used in the course of synthesis of a diterpene lactone. Entry 6 is a case in which PdCl2 catalyzes both the formation and rearrangement of the reactant. 

During the study of the isomerization of diallyl ether with catalysts of this type, it was observed that the nature of the complex anion (Y) has a profound influence on the relative rate of isomerization with respect to cyclization. Diallyl ether can be isomerized to a mixture consisting mainly of allyl propenyl ethers (44) with a small amount of 2-methyl-3-methylene-tetrahydrofuran (45) and dipropenyl ether (46) the catalyst for this... 

Polarization of double bonds due to the electron releasing effect of thioalkyl groups in thioenol ethers is much weaker than that reported for enol ethers (Table 4.26), as can be verified for the (E) and (Z) isomers of methyl propenyl sulfide in Table 4.40 [326, 327]. 

An acetal tethered compound can easily be prepared by treatment of equimolar amounts of a 2-propenyl ether derivative of a saccharide with a sugar hydroxyl in the presence of a catalytic amount of acid. Activation of the anomeric thio moiety of the tethered compound with N-iodosuccinimide (NIS) in dichloromethane results in the formation of the p-linked disaccharide. In this reaction, no a-linked disaccharide is usually detected. It is of interest to note that when this reaction was performed in the presence of methanol, no methyl glycosides are obtained. This experiment indicates that the glycosylation proceeds via a concerted reaction and not a free anomeric oxocarbenium ion. 

The reaction of linalool with boron trifluoride etherate has been re-examined no pinenes or camphene were obtained.146 Dehydrolinalool reacts with methyl iso-propenyl ether under acidic conditions by Claisen rearrangement to give the allene (58).147 Further papers in this section include reaction of monoterpenoid alcohols with paraformaldehyde-acetic anhydride-sodium acetate,148 rearrangement of the alcohol (47 X = OH) to the oxabicycloheptane (59) and the ketone (60),149 and the rearrangement of a typical monoterpenoid vicinal hydroxy-ester to an epoxide.150... 

The use of DCP-derived propenyl ethers in nitroalkene [4 + 2] cycloaddition allows for the installation of an additional stere-ogenic center in the tandem cycloadducts. The methyl substituent also provides a stereochemical marker to allow for the determination of endo/exo selectivity in the [4 + 2] cycloaddition. DCP-derived E-propenylvinylether (E-4) has been employed in the... 

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