Ethylidene transfer

Asymmetric ethylidene transfer has been achieved in the reactions of 1-cyclohexenyl ethers carrying a chiral auxiliary with 1,1-diodoethane/diethylzinc 39. Asymmetric induction in the reaction of diazofluorene with fumaric esters bearing chiral alcohol moieties has been investigated (equation 84)140,141. Kinetics of intramolecular cyclopropanation in... 

If cyclopentene would react pair-wise with 2-pentene, only one product would form, namely 2,7-decadiene, and a similar result for cyclodimers etc. of cyclopentene. If somehow, the alkylidene species would be transferred one by one, we would obtain a mixture of 2,7-nonadiene, 2,7-decadiene, and 2,7-undecadiene in a 1 2 1 ratio. The latter turned out to be the case, which led the authors to propose the participation of metal-carbene (metal alkylidene) intermediates [6], Via these intermediates the alkylidene parts of the alkenes are transferred one by one to an alkene. The mechanism is depicted in Figure 16.4. In the first step the reaction of two alkylidene precursors (ethylidene -bottom- and propylidene -top) with cyclopentene is shown. In the second step the orientation of the next 2-pentene determines whether nonadiene, decadiene or undecadiene is formed. It is clear that this leads to a statistical mixture, all rates being exactly equal, which need not be the case. Sometimes the results are indeed not the statistical mixture as some combinations of metal carbene complex and reacting alkene may be preferred, but it is still believed that a metal-carbene mechanism is involved. Deuterium labelling of alkenes by Gmbbs instead of differently substituted alkenes led to the same result as the experiments with the use of 2-pentene [7],... 

Oxidation of trows-RuCl(C=CCH Ph2)(dppe)2 favors hydrogen atom transfer leading to frons-[RuCl(=C=CHCHPh2)(dppe)2] [217]. Chemical oxidation of Ru (C=CRc)(PPh3)2Cp (Rc = ruthenocenyl) gives the cydopentadienylidene-ethylidene... 

The reflux condenser is replaced by a Claisen distillation head, and the reaction mixture is distilled until the temperature of the vapor reaches 140°. The residue is transferred to a smaller flask and fractionated through a 30-cm. column packed with glass helices. A low-boiling fraction containing ethylidene diacetate and diethyl malonate is collected first, followed by 79-89.5 g. (68-77%) of diethyl ethylidenemalonate b.p. 102-106°/10 mm. %>5 1.4394 (Note 1). 

The application of carbenoid reactions, however, gives satisfactory results in certain cases. Thus, ethylidene iodide with diethylzinc transfers an ethylidene group to olefinic double bonds in good yields ". The reaction proceeds in a stereospecific manner (equation 50). Stereochemical control of the addition by hydroxyl groups similar to those... 

The next step in the reaction scheme—decomposition of the a-bonded alkylpalladium (XIV or XV)—has caused some controversy. To account for the results of several deuterium-labelling studies (15, 36, 54), a. palladium-assisted hydride transfer reaction (Reaction 4) has been proposed (36, 54). A number of inconsistencies in the studies using 2-deuteropro-pylene as substrate (54) have been discussed (i). In addition, the formation of a free carbonium ion such as VII [as proposed by Moiseev (36)], while accounting well for the formation of ethylidene diacetate, is much less satisfactory in accounting for the production of the unsaturated esters in an acetate-acetic acid medium. A simple elimination of -hydrogen (Reactions 13a and b) could also account for the products formed. While not necessary for the reaction, chloride assistance for proton removal is a possibility and has been postulated previously for a similar reaction (i, 37). 

Formation of 1,1-diacetates—e,g., ethylidene diacetate from ethylene or hexylidene diacetate from hexene—by simple acetate displacement of palladium (Reaction 16) is a much more satisfactory reaction scheme than any previously proposed. On the other hand, accounting for 1,2-diol type products is diflBcult by this scheme, necessitating a reverse hydrogen transfer to form a two-carbon insertion product intermediate. This type... 

Glebova, Z.I., Eryuzheva, O.V., and Zhdanov, Y.A., Simple method for synthesizing carbohydrate-containing a,P-epoxy phosphonates from l-O-tosyl-3,5 4,6-di-O-ethylidene-L-AyZo-hex-2-ulose under phase-transfer catalysis, Zh. Obshch. Khim., 63, 1677, 1993 Russ. J. Gen. Chem. (Engl. Transl.), 63, 1172, 1993. 

Similar effects are observed for phosphonium ylides18 (see also Vol. El, p 704) which are able to transfer their alkylidenc unit to a,/ -unsaturated esters. The ring closure of the intermediate betaine proceeds under steric control and preferentially generates the less hindered cyclopropane derivatives, for example, ethylidene triphenylphosphorane and methyl (E)-2-butenoate furnish a 93 7 mixture of methyl 2,3-dimethylcyclopropanecarboxylate 519. 

Amorphous copolymers of ethylene and propylene, EPM, also possess rubber-elastic properties. But they cannot be vulcanized with sulfur because of the absence of carbon-carbon double bonds, and so a special technique using peroxides as free radical sources for transfer reactions has had to be developed. However, polymerizing in a diene component such as, for example, cyclopentadiene or ethylidene norbornene, leads to the formation of what are known as EPDM rubbers with double bonds in the side chains. These can, on the one hand, be vulcanized in the classic way with sulfur, but, on the other hand, still have good aging properties. Consequently, EPDM rubbers are mainly used in automobile construction, the cable and construction industries, as well as for technical purposes. However, the EPDM rubbers have only slight self-adhesion, so that producing tires from cut sections is made more difficult. It is for this reason that EPDM rubbers are not used for tires. 

Methylenecyclopropcmes. The preparation of 6-methylenebicyclo[3,l,0]hexane (122) from tosylhydrazides (120) and (121) involves methylene-cyclopropane rearrangement. The high-temperature isomerization of equilibrium mixtures of ethylidene-cyclopropane and methylmethylene cyclopropane to isoprene is thought to proceed by way of a biradical intermediate which suffers 1,4-hydrogen transfer. The tetra-cyclononane (267) does not undergo [ 2 -I- 2j cycloaddition, but affords (268) by way of geometrical isomerization and ene reaction. ... 

In the biosynthesis of plant sterols, the side chain may be subject to further methylations, all dependent on SAM as the methyl donor. The 24a-ethyl groups found in sitosterol and stigmasterol are formed by the transfer of a methyl group to a 24-methylene sterol, which is generated as shown above the resulting Z-24-ethylidene sterol intermediate is isomerized to a A -24-ethyl sterol whose C-24(25) double bond is subsequently stereospecifically reduced by an NADPH-dependent sterol A -reductase. 

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