Terminal vinyl groups

Constmction of multilayers requires that the monolayer surface be modified to a hydroxylated one. Such surfaces can be prepared by a chemical reaction and the conversion of a nonpolar terminal group to a hydroxyl group. Examples of such reactions are the LiAlH reduction of a surface ester group (165), the hydroboration—oxidation of a terminal vinyl group (127,163), and the conversion of a surface bromide using silver chemistry (200). Once a subsequent monolayer is adsorbed on the "activated" monolayer, multilayer films may be built by repetition of this process (Fig. 8). 

A series of 2-vinyl-3-silyloxybicyclo[3.2.0]heptan-6-ones has also been converted to prostanoid lactones in excellent yield but variable regioselectivity. Some of the best regioselectivity was obtained using H202 in trifluoroethanol (see p. 1097).241 The strained cyclobutanone ring and the relatively unreactive terminal vinyl group favor the desired reaction in preference to alkene epoxidation. 

Reaction sequence E removed an extraneous oxygen by Sml2 reduction and installed an oxygen at C(15) by enolate oxidation. The C(l) and C(15) hydroxy groups were protected as a carbonate in Step E-5. After oxidation of the terminal vinyl group, the C-ring was constructed by a Dieckmann cyclization in Step F-4. After temporary protection of the C(7) hydroxy as the MOP derivative, the (1-ketoestcr was subjected to nucleophilic decarboxylation by phenylthiolate and reprotected as the BOM ether (Steps F-5, F- 6, and F-7). 

We can incorporate short chain branches into polymers by copolymerizing two or more comonomers. When we apply this method to addition copolymers, the branch is derived from a monomer that contains a terminal vinyl group that can be incorporated into the growing chain. The most common family of this type is the linear low density polyethylenes, which incorporate 1-butene, 1-hexene, or 1-octene to yield ethyl, butyl, or hexyl branches, respectively. Other common examples include ethylene-vinyl acetate and ethylene-acrylic acid copolymers. Figure 5.10 shows examples of these branches. 

To compare the predictions of the various molecular theories of rubber elasticity, three sets of high functionality networks were prepared and tested In this Investigation. The first set of networks tested were formed In bulk and attained a high extent of the endllnklng reaction, i.e., eX).9 where e Is the extent of reaction of the terminal vinyl groups. The second set of networks studied were formed In the presence of diluent and also achieved a high extent of reaction (e>0.9). The final group of experiments were performed on networks formed In bulk at low extents of reaction (0.4 [Pg.333]

Phenylquinoxaline oligomers have also been end-capped with 4,4 -divinylbenzil (48). The terminal vinyl groups underwent a thermally induced crosslinking reaction to yield materials with high TgS (-390°C) but poor thermooxi dative stability. 

The first-order rate constants for terminal vinyl groups and for trans-vinylene groups in linear polyethylene were observed by Dole and Williams (8) to be 20 to 30 times higher than our corresponding rates in the amorphous trans- and vinyl polybutadienes (Table III). On the other hand, the initial yields were lower than our G0 values because of the... 

The most straightforward application of the Grubbs reaction is to effect homologation of a terminal vinyl group. One concern with the use of the second generation Grubbs catalyst 3 is the cost, about 100/mmol. In conjunction with a total synthesis of the macrolide RK-397, Frank McDonald of Emory reported (J. Am. Chem. Soc. 126 2495, 2004) that the conversion of 1 to 2 required 10 mol % of 3, but that it proceeded efficiently with just 2 mol % of the Hoveyda Ru catalyst 4 (J. Am. Chem. Soc. 122 8168,2002). The alkene so prepared was cleanly trans. An advantage of 4 is that it avoids the use of the expensive PCy,. 

A simple yet powerful application of the Grubbs reaction is specific homologation of a terminal vinyl group. When there is more than one alkene in the molecule, suitably disposed, one would worry about competing cyclizalion. In studies directed toward the cryptophycins, Mark Lautcns of the University of Toronto has reported (Organic Lett. 2004,6, 1883) that the second generation Grubbs catalyst 2 smoothly converts 1 to 3. The alternative cyclization product 4 is produced only in trace amounts. 

The first-developed method for the enantioselective construction of secondary aminated stereocenters, by Knowles, was the hydrogenation of enamides such as II. In the context of a synthesis of BILN 2061 15, an antiviral protease inhibitor, Anne-Marie Faucher of Boehringer-Ingeiheim, Laval has shown (Organic Lett. 2004, 6, 2901) that such hydrogenations can be effected even in the presence of a terminal vinyl group. The product 12 was carried on to 15 over several steps, including the Ru (Hoyveda) cyclization of 13 to 14. 

The presence of a (i) carbonyl, (ii) sulfonyl or (iii) phosphoryl group at the a-carbon of a terminal vinyl group (Figure 14.21) can polarize the double bond and... 

Cyclizations of chloral hemiacetal derivatives of cyclic allyl alcohols were regio- and stereo-selective (Table 6, entry 1), but a mixture of regioisomers was obtained from analogous derivatives of acyclic allyl alcohols with a nonterminal double bond.93 Hemiacetal derivatives of allyl alcohols with a terminal vinyl group have been cyclized with mercury(II) acetate to give acetal derivatives of threo 1,2-diols with moderate selectivities (equation 54 and Table 15, entries 1 and 2).147 Moderate to excellent stereoselectivity has been observed in the iodocyclizations of carbonate derivatives of allyl alcohols (entries 3-5).94a The currently available results do not provide a rationale for the variation in observed stereoselectivity. 

The cyclization of carbamate derivatives of unsaturated amines has proven synthetically useful. Cyclizations of carbamates of allylamines containing a terminal vinyl group give oxazolidinone products (equation 60 and Table 17, entries 1 and 2).99,161 Bromocyclizations of systems with a di- or tri-sub-stituted alkene often give mixtures of oxazolidinones and tetrahydrooxazinones,163 while cyclization of an A -cinnamyl carbamate with phenylsulfenyl chloride gave only the oxazolidinone product.163b,163c The stereochemistry of the cyclization of primary carbamates of either allylic or homoallylic amines is low... 

Strained rings may be opened by a ruthenium carbene-catalyzed reaction with a second alkene following the mechanism of the Cross Metathesis. The driving force is the relief of ring strain. As the products contain terminal vinyl groups, further reactions of the Cross Metathesis variety may occur. Therefore, the reaction conditions must be optimized to favour the desired product. 

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