Alkoxy-3-ethylenes

Lithium ethylamine Ethylene derivs. from alkoxy-2-ethylenes... 

Heptylmagnesium chloride in ether or tetrahydrofuran added at -5 to some CuBr in a soln. of acrolein diethyl acetal in tetrahydrofuran, and the product isolated after 2 hrs. product (mixture of cis- and trans-isomtrs), Y 89%. F. e. and limitations s. J. F. Normant et al., Tetrah. Let. 1975, 3833 synthesis of ethylene derivs. from alkoxy-2-ethylenes cf. ibid. 1975, 3837. 

There are a number of other mechanisms by which alkenes can undergo photochemical f2 + 2) cycloaddition, one of which works well for electron-rich alkenes and electron-acceptor sensitizers. The pathway is through the radical cation of the alkene, which attacks a second, ground-state alkene molecule and then cydizes and accepts an electron to give the product cyclobutane. Typical of this group of reactions is the formation of 1,2-dialkoxycydobutanes from alkoxy-ethylenes with drcyanonaphthalene as sensitizer 12.78). 

Chemical Structure and Properties. Homopolymer consists exclusively of repeating oxymethylene units. The copolymer contains alkyhdene units (eg, ethyUdene —CH2—CH2—) randomly distributed along the chain. A variety of end groups may be present in the polymers. Both homopolymer and copolymer may have alkoxy, especially methoxy (CH3 O—), or formate (HCOO—) end groups. Copolymer made with ethylene oxide has 2-hydroxyethoxy end groups. Homopolymer generally has acetate end groups. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

In these studies cleavage of the endocyclic alkoxy group produces ethylene glycol and since only about 5% was found, it was concluded that hydrolysis proceeds 95% via exocyclic cleavage, in excellent agreement with results found for poly(ortho esters). 

IR Isoprene rubber poly (els-1,4-isoprene) PEO Poly(ethylene oxide) a-Alkoxy- >-hydroxy polyethylene oxide... 

Since alkoxy radicals are known precursors to chain scission in autoxidation (24), the "hot" alkoxy radicals formed as shown should undergo facile chain scission or fragmentation. The chain scission is illustrated for the alkoxy radical derived from either the ethylene or propylene monomer unit in EPM ... 

Alkoxy-l,3-dithia-2-phospholane ( O-Alkyl ethylene dithiophosphate )... 

The preference of the distal attack of olefin (ethylene) on nitronate (257) could be attributed to steric hindrances due to the presence of the axial alkoxy substituent at the C-6 atom, which shields the proximal attack. These hindrances are absent in nitronate (256). However, one could suggest that for nitronate (256) adopting a half-chair conformation, the approach of olefin from the side of the C-6 atom is more shielded even if the C-6 atom is unsubstituted because considerably deviates upward from the plane of the C=N bond of the dipole in comparison to the deviation of the C-5 atom in the opposite direction (see Sections 3.3.3 and 3.5.2). It could be worthwhile to combine this approach with a consideration of the facial preference for model nitronates substituted at the C-5 atom also. 

It should additionally be noted that a number of the paths of the schemes above have received some confirmation in a number of literature reports dealing with the photolysis and photo-oxidation of other polyesters [32-35], Because these reports investigated poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) and poly(butylene naphthalate), however, they may not have direct application to understanding of the processes involved in PET and PECT and so have not been discussed in this present chapter. All do contain support for the formation of radicals leading to CO and C02 evolution, as well as the hydrogen abstraction at glycolic carbons to form hydroperoxides which then decompose to form alkoxy radicals and the hydroxyl radical. These species then were postulated to undergo further reaction consistent with what we have proposed above. 

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