Reaction olefin displacement

Etherification. Ethers of amyl alcohols have been prepared by reaction with ben2hydrol (63), activated aromatic haUdes (64), dehydration-addition reactions (65), addition to olefins (66—71), alkoxylation with olefin oxides (72,73) and displacement reactions involving thek alkah metal salts (74—76). 

In the production of a-olefins, ethylene reacts with an aluminum alkyl at relatively low temperature to produce a higher aLkylalumiaum. This is then subjected to a displacement reaction with ethylene at high temperatures to yield a mixture of a-olefins and triethylalumiaum. In an alternative process, both reactions are combiaed at high temperatures and pressures where triethylalumiaum fuactioas as a catalyst ia the polymerization process. 

Other examples of the successful displacement of tosylates are the preparation of 31 -, 16a-,16j - and27- labeled steroids. This displacement reaction fails, however, with certain C-18 and C-19 alcohol derivatives which give mainly O—S instead of C—O bond cleavage. Unsatisfactory results were also obtained with sterically hindered tosylate esters at C-11, C-12 and C-20, which give considerable amounts of olefinic products in addition to O—S bond cleavage. ... 

Azaloxan (12) is an antidepressant agent. Its synthesis can be accomplished starting with the reaction of catechol (7) and 3,4-dibromobutyronitrile (obtained by addition of bromine to the olefin) to give l,4-benzodioxan-2-ylacetonitrile (8). A series of functional group transformations ensues [hydrolysis to the acid (9), reduction to the alcohol (10) and conversion to a tosylate (11)] culminating in an SN-2 displacement reaction on tosylate 11 with l-(4-piperidinyl)-2-imidazolidi-none to give azaloxan (12) [3]. 

The cyclic bromonium ion was first used to explain the stereochemistry and course of the bromination of olefins and later proposed as an intermediate in the displacement reaction 232 288 Y... 

Several very stable radicals (e.g. those derived from AIBN) react with tetraphenyl-biphosphine in a homolytic displacement reaction.39 Phosphoranyl radicals, e.g. (36), were postulated as being intermediates. The reaction of the triplet state of olefin (37) is thought to occur via a similar mechanism. 

This chemistry is sometimes accomplished simultaneously in one reactor and sometimes in two separate reactors. In the former, the triethyl aluminum catalyst is lost in the latter, it is recycled. Sometimes the displacement compound is butene-1 or hexene-1, depending on the chain length of the final alpha olefin desired and the change in operating conditions necessary to effect the displacement reaction. 

Insignificant impurities of heavy metals (e.g. nickel) in a reactive medium or equipment material can cause a secondary displacement reaction which forms higher olefines ... 

While the original synthesis of 1 features a clever use of the Tebbe olefination reaction, the process routes use elegant methods to set the ring stereochemistry through displacement reactions (and equilibration), followed by reduction, reactions that are much more scalable. This difference reflects the contrasting need for SAR development in the medicinal chemistry work vs. the need for scalability in the process work. 

The molybdenum complexes (olcfin)Mo(CO)3 of C3H3 and CgHio react readily with CO to yield (olcfin)Mo(CO)4 in which the molybdenum atom is coordinated to the 1,5-double bonds (32a) and (32b) (323). Prolonged reaction with CO results in complete displacement of olefin... 

Displacement reactions on 1,1-disubstituted cyclopropanes have been used to prepare other cyclopropanone equivalents. The most readily available 1,1-disubstituted cyclopropanes are geminal dihalo derivatives prepared by the addition of dihalocarbenes to olefins. Unfortunately, these materials do not undergo direct displacement easily and therefore do not provide a general route to other cyclopropanone derivatives. Solvolysis usually leads to ring-opened products, although dibromocyclopropanes with a barrier to... 

The two compounds, bis (cyclo-octadiene) nickel and (cyclo-octatetraene) nickel, can also be synthesized directly by reduction of nickel acetylacetonate in the presence of olefins. But bis (cyclo-octatetraene) nickel is obtained only by a displacement reaction on the centro-nickel compound. 

Displacement Reaction. Much of what has been said about the alkylation reaction is also valid for the displacement reaction. Here also it is of importance to keep the nickel level as low as possible, not only to prevent isomerization and branching during displacement, but especially to circumvent trouble during the subsequent separation of TEA from olefins. 

At least 20 p.p.m. of nickel (TEA basis) are required in order to obtain 97 to 99% displacement within 2 hours (200° F., 2000 p.s.i. of ethylene). After completion of the reaction, when the ethylene pressure is released, a displacement reaction product containing traces of nickel catalyst tends to revert to alkylaluminum. This reaction takes place slowly at room temperature and atmospheric pressure, but the rate accelerates at the conditions required for TEA-olefin separation. It is no surprise, then, that even after only a few seconds contact a significant amount of back-alkylation will take place. 

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