Propenyl group, determination

A new series of functionalized poly(arylene ether ketone)s and their use as modifiers for bismaleimide resins has recently been published (96). In contrast with the former work in this area, the functional groups are not terminal but randomly distributed along the backbone of the poly(arylene ether ketone). The synthesis involves the reaction of 4,4 -difluorobenzophenone and the potassium bisphenates of bisphenol-A and 2,2 -bis(3-allyl-4-hydroxyphenyl) hexafluoro-isopropane or mixtures thereof in DMAc at 155 °C as outlined in Fig. 31. The concentration of the o,o -diallylbisphenol employed in the synthesis determines the concentration of functional propenyl groups. 

Three different principles of selectivity are required to achieve this result. First, the difference in rate of epoxidation by the catalyst of a disubstituted versus a monosubstituted olefin must be such that the propenyl group is epoxidized in complete preference to the vinyl group. The effect of this selectivity is to reduce the choice of olefinic faces to four of the two propenyl groups. Second, the inherent enantiofacial selectivity of the catalyst as represented in Figure 6A.1 will narrow the choice of propenyl faces from four to two. Finally, the steric factor responsible for kinetic resolution of 1-substituted allylic alcohols (Fig. 6A.2) will determine the final choice between the propenyl groups in the enantiomers of 80. The net result is the formation of epoxy alcohol 81 and enrichment of the unreacted allylic alcohol in the (35)-enantiomer. 

Optically active ran -l,2-bis( ra -propenyl)cyclobutane (TTT) and trans-X-(cw-propenyl)-2-( ran -propenyl)cyclobutane (TCT) were pyrolyzed to determine the extent of involvement of all possible 1,3-shift stereopathways. The results were similar in each case leading to an average of 50.0 45.5 40.5% utilization of the si, sr, ar, and ai pathways, respectively (Scheme 9.81). Remarkably, only rran -propenyl groups can function as the three carbon unit of the 1,3-shift, and the cw-propenyl group apparently only functions as the migrating group. 

Unsaturation value can be determined by the reaction of the akyl or propenyl end group with mercuric acetate ia a methanolic solution to give acetoxymercuric methoxy compounds and acetic acid (ASTM D4671-87). The amount of acetic acid released ia this equimolar reaction is determined by titration with standard alcohoHc potassium hydroxide. Sodium bromide is normally added to convert the iasoluble mercuric oxide (a titration iaterference) to mercuric bromide. The value is usually expressed as meg KOH/g polyol which can be converted to OH No. units usiag multiplication by 56.1 or to percentage of vinyl usiag multiplication by 2.7. 

Simple derivatives of the parent compound in this group, exo,endo- and o ,o -2,6-dimethyl-l-phosphabicyclo[2.2.1]-heptane 211 and 212, have been synthesized by the cyclization of 2-methyl-4-(2-propenyl)phospholane in the presence of base <2002ZFA580>. The structures were determined via spectroscopic means as well as X-ray crystallography and further confirmed by reactions with selenium, sulfur, (CH3)2SeO, CH3I, and HS03F. 

Enantiomerically pure vinyl sulphoxides are highly diastereoselective Michael acceptors with a variety of nucleophiles97. However, the transition states that determine the stereochemical outcome are not easy to predict. For example, the nucleophilic attack of piperidine on (—)-(/ )-(Z)-propenyl p-tolyl sulphoxide98 gives a product that can be explained by approach of the nucleophile from the side of the tolyl group, away from... 

Highly stereoselective preparation of either trans- or m-/J,y-dia1kyl-y-lactam derivatives is achieved by cyclization of l-methyl-2-propenyl trichloroacetamides. The choice of the nitrogen protecting group controls the steric outcome of the reaction. The mechanistic aspect that determines this stereoselectivity is unclear26. 

The first attempt to determine the stereochemistry of vinylcyclopropane rearrangement utilized methyl groups at both C2 and C2. Thus, optically active fra/25 -2-methyl-l-(rra/25 -propenyl)cyclopropane was pyrolyzed, and after correction for the racemization of starting material, it was concluded that the cyclopentenes were formed in a 65 22 8 5 ratio via the si sr ar, ai pathways, respectively. Thus, 73% of the reaction occurs by the allowed pathway. However, this result could have been prejudiced by the fact that the si and ar products are more stable than the forbidden products. Unfortunately, cis isomer could not be subjected to the pyrolytic rearrangement because another reaction, namely the homo-1,5-hydrogen shift to substituted dienes occurred (Scheme 6.18). 

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