Vinyl residual

In accordance with the structure of chlorophyll c, it is hypothesized that its biosynthesis comes from protochlorophyllide a by dehydrogenation of the side chain at C-17. Chlorophyll d should arise from chlorophyll a by oxidation of the C-3-vinyl residue, but at which stage of chlorophyll biosynthesis this occurs is unknown. The biosynthesis of bacteriochlorophylls seems to follow the same general pathway of higher plants, according to studies performed with chlorophylhde and bacterio-chlorophyU enzymes. ... 

An oxidase first converts two of the propionate groups (R2) into vinyl residues. The formation of protoporphyrinogen IX completes the modification of the side chains. 

Precursors. The precursors for this reaction are anthocyanins, flavanols or flavanols containing a vinyl residue at C-8 (i.e., 8-vinylflavanols). 8-Vinylflavanols could arise from the cleavage of flavanol-ethyl-flavanol oligomers or from the dehydration of the flavanol-ethanol adduct formed after the attack of aldehyde cation to the flavanol (Chapter 9B). Saucier et al. (1997) have supported evidence for this precursor when detecting an ion corresponding to vinyl-catechin from the fragmentation of ethyl-linked catechin dimers under ESI-MS in positive or negative mode. 

A binding site consists of a polymerisable group, generally a vinyl-type monomer, with a second functional group attached, capable of interacting with the template molecule. After polymerisation the vinylic residue is part of the... 

The clear-cut behavior in the opening of epoxides can sulfer some exceptions. Such abnormal reactions have been reported in the opening of epoxide 21 with vinylmagnesium bromide. In this case, the vinyl residue was introduced at C2 as expected but with retention of configuration this is because of preferential opening with the bromide ion followed by the displacement of the bromide atom with the carbon nucleophile [34]. 

Although examples continue to be reported in which only an unsubstituted vinyl residue is ti ansferred [5-11], the important feature of transfer from tin is that it occurs in a stereospecific manner. So far, only one example (Scheme 4-1) appears to have been described in which complete double-bond isomerization occurs [12]. 

The Stille coupling has also found a use in medicinal chemistry the incorporation of carbon-11 (half-life 20.3 min) to give products which are applicable in positron emission tomography has been described [182] aryl or vinyl residues can be transferred from tin in reactions with labeled methyl iodide which are complete in only 4 min ... 

The quinuclidine part of quinine has three asymmetric carbon atoms at positions 3, 4 and 8, of which C-3 is attached to a vinyl residue. Thus the simplest approach to molecular modification may involve replacement of the quinuclidine by other bases. It is also possible that the vinyl group may be saturated, altered or removed to get compounds with different electronic and steric nature. Replacement of the quinuclidine moiety in quinine by a 2-piperidyl ring gave 28, which lacks asymmetry at carbons 3 and 4 [53], Both the racemates of 28 were found to possess slight activity [54], thereby indicating that asymmetry at positions 3 and 4 -may not be essential for antimalarial activity [53,55]. Consequently a series of 4-quinolinylalcohols... 

Rhodium carbonyi clusters. 13,288 15, 334 18, 305-306 19, 280-281 20, 317-318 Hydroformylation. A phosphine plays a crucial role to suppress hydrogenation during hydxoformylation of 4-vinylpyridine. The A-vinyl group of a divinylpyrrole can be retained to achieve selective hydroformylation of a carbon-linked vinyl residue. ... 

M6 19,280-281 20,317-318 role to suppress hydrogenation. 1 group of a divinylpyrrole can be n-Imked vinyl residue. ... 

A useful synthesis of copropotphyrin III and related compounds has now been achieved by modification of protoporphyrin IX the key reaction in this process is the terminal oxidation of the vinyl residues by thaliium(UI) trifluoroacetate (Scheme 6) this has now been utilized for the preparation of a specifically C-labeled coproporphyrin III required for biosynthetic studies. Further adaptation of this process has allowed the preparation of a range of other intermediates and analogs between copro- and protoporphyrin, including hardero-, pempto-, and chlorocruoroporphyrin and their isomers, as well as dihydroprotoporphyrin. ... 

However, it was still necessary to develop a technology capable of achieving substitution of vinyl residues on the glassine leaflets under industrial conditions. Such substitutions are possible by classical chemistry in organic solvents, or allegedly without solvent, but not on an industrial scale. " ... 

The first diastereoselective synthesis of methyl (3R,7R)-jasmonate is attributed to Gerhard Quinkert. [94] In the initial step, starting from bis-(8-phenyhnen-thyl) malonate, a vinylcydopropane is constructed. After removal of the chiral auxiliary, the cyclopentanone is built up by means of a domino homo-Michael reaction / Dieckmann cydisation. Attack of dimethyl pent-2-ynylmalonate leads to inversion at the stereogenic centre at the vinyl cyclopropane. After decarboxylation, the vinyl residue is transformed into an ester group and the triple bond hydrogenated with a Lindlar catalyst. 

Access to Dieno-Pyranosides. We were interested in developing synthetic schemes to dieno-pyranosides V (Figure 3a), and dieno-pyranosides VI. Systems type V are less reactive fiian their demethylated analogs VI (6) (the steric interaction of the methyl group with the vinyl residue causes the s-cis rotamer required for the... 

Vinyl Magnesium Route. A direct route to dieno-p osides or VI) is shown in Figure 3b, introduction of the vinyl residue is effect by reacdon of vinyl magnesium bromide and a pyranoside-ulose VII (, follow by eliminadon of the tertiary hydroxyl group in VIII. This route could, in pnnciple, be common for both methyl, and desmethyl dienic systems.. ... 

Both linear and cyclic acetals with vinyl residues copolymerize in an alternating fashion with MA. Two good examples are the copolymers prepared from the O-vinyl acetals of formaldehyde or acetaldehyde and 2-vinyl-l,3-dioxalane. The monomer 4-methylene-2-(trichloromethyl)-l,3-dioxolane also copolymerizes in a 1 1 fashion with MA, regardless of the initial monomer feed ratio in the reaction mixture, duration of reaction time, and monomer conversion. l,3-Dioxep-5-enes are also cyclic acetals. The copolymerization of these monomers with was discussed in... 

The aa- and -monomers, i.e., dimethallylidenepentaerythritol 28B and dicrotyllidenepentaerythritol 28C, under the same free-radical-initiated copolymerization conditions, also give copolymers with MA. Copolymerizations must be carried to low conversion to get soluble copolymers. In all three cases, the maximum rates of copolymerization occurred at a monomer mixture ratio of (28A-28C)/MA of 0.5. Copolymer compositions and IR and NMR studies indicated that 1 1 copolymerization was achieved between each vinyl residue and MA. ... 

A variety of heterocyclic compounds with vinyl residues, such as N-... 

The distance of the asymmetric carbon atom from the vinyl residue of the backbone is an important factor both for the model and the polymer. 

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