Reduction olefin

Dibromo adducts have been used for many years for purifying olefins. Reduction with zinc or iodide has been the traditional way of regenerating the olefin, although occasionally other reagents, ferrous chloride, for example, have been employed. Zinc is usually effective and may be used in acetic acid in favorable cases. Milder conditions are necessary if sensitive groups are present (ref. 185, p. 51). A well known application of the protective function... 

Scheme 5.11 Sulfoxide-directed olefin reduction-model compounds.

Scheme 5.12 Sulfoxide-directed olefin reduction-proof of concept.

Scheme 5.13 Chiral sulfoxide preparation and olefin reduction with borane.

To gain understanding of the interdependence between the olefin reduction and the sulfoxide reduction, the saturated sulfoxide 52 was prepared and treated with BH3-THF. No reaction was observed under the similar conditions (Scheme 5.18). The unactivated vinyl sulfide 16 was also not reactive toward BH3-THF. These results indicated that sulfoxide and olefin were reduced simultaneously, not independently. Again this phenomenon was unexpected and pointed to the unique nature of this reaction. 

RuCl2(PPh3)3 has been shown to catalyze the reduction of several aldehydes, but does not have widespread scope. This catalyst is not chemoselective and, in the presence of alkenes, would favor olefin reduction over that of the aldehyde. Noyori and coworkers showed that chemoselectivity is easily introduced by the addition of ethylene-diamine as a ligand (Scheme 15.6) [29, 30]. This system requires the presence of co-catalytic KOH/i-PrOH as an activator. 

Olefins plant separation train, 20 776 Olefins reduction, in gasoline, 11 689 a-Olefin sulfonate (AOS), 17 725-726 ... 

Another stereoselective synthesis (Scheme 11) is based on sugar aldehyde 35 and intermediate 36 subsequent 1,2-O-isopropylidine deprotection, N,0-debenzylation/olefin reduction/reductive cyclization in a single pot, and O-acetylation result in the formation of bicyclic aza sugar 37 (09TA1217). 

Olefin Reductions—Alkylation capacity would increase with any reduction in olefin content because it would provide a way to use the C4 and some C5 olefins in gasoline. New isomerization capacity would be needed if substantial quantities of C5 and C6 olefins had to be removed. The C5/C6 olefins would have to be hydrogenated and isomerized to make up part of the octane loss. 

The discovery by the recent Nobel-laureate, Ryoji Noyori, of asymmetric hydrogenation of simple ketones to alcohols catalyzed by raras-RuCl2[(S)-binap][(S,S)-dpen] (binap = [l,l -binaphthalene-2,2/-diyl-bis(diphenylphosphane)] dpen = diphenylethylenediamine) is remarkable in several respects (91). The reaction is quantitative within hours, gives enantiomeric excesses (ee) up to 99%, shows high chemoselecti-vity for carbonyl over olefin reduction, and the substrate-to-catalyst ratio is >100,000. Moreover, the non-classical metal-ligand bifunctional catalytic cycle is mechanistically novel and involves heterolytic... 

This section contains dehydrogenations to form olefins and unsaturated ketones, esters, and amides. It also includes the conversion of aromatic rings to olefins. Reduction of aryls to dienes is found in Section 377 (Olefin-Olefin). Hydrogenation of aryls to alkanes and dehydrogenations to form aryls are included in Section 74 (Alkyls, Methylenes, and Aryls from Olefins). 

The synthesis of the 1,6-linked ester was straightforward as outlined in Scheme 6. We were able to convert alcohol 23 to aldehyde 24 using Swern oxidation conditions. Wittig reaction was followed by olefin reduction and saponification to bring the sequence as far as 26. Esterification of 26 with olefin alcohol la, mediated by DCC, then afforded the target ester 27 in good overall yield (13). 

Besides reduction, other transformations were performed, for example, reductive amination, nucleophilic 1,2-addtion, deoxygenation or olefination/reduction and thionation (Enders and Grondal 2006 Grondal 2006). 

One option from UOP for olefin reduction is the revamp of an FCC unit to RxCat technology (10). In the RxCat process, Figure 4.6, a portion of coked catalyst is recycled to mix with regenerated catalyst at the bottom of the riser reactor. This feature allows the unit to run at a higher catalyst-to-oil ratio and a lower catalyst contact temperature. Moreover, ZSM-5 additive is more effective with RxCat because coked ZSM-5 retains more activity than coked Y zeolite. 

RxCat technology continues the 50-year historical extension of improvements in FCC technology, with gasoline olefin reduction as an additional measure of efficiency. 

The proposed reaction mechanism (see Scheme 4) is similar to that which is well established for olefin reduction, with the insertion of a meial-hydride bond into the carbonyl group coordinated to (he metal center. A mechanism in which reduction occurs by a simple nucIcopliiUc attack of the hydrogen atom of the transition metal hydride (which behaves like Blit or AlHa ) into the carbonyl group of the aldehyde, cannot be ignored ... 

Complementary to catalytic hydrogenations, the use of diborane provides convenient routes towards the elimination of olefins. However, this reaction has the added advantage of introducing new functionality at the site of olefin reduction. Because of regiochemical considerations, this reaction is particularly useful when applied to exocyclic olefins. Scheme 6.76 shows that a sugar derivative was treated with diborane with an oxidative workup to yield the illustrated product bearing a new hydroxyl group exclusively at the primary center [117]. 

Another popular olefination-reduction sequence starts with commercially available ketone 122, transformed into olefin 123 using a Wittig or Wittig-Horner reaction [103] (illustrated in Scheme 11.32). Reduction of the double bond proceeds with high stereocontrol to yield the alio derivative 124. The cis arrangement at C2-C3 allowed formation of lactone 125 and the synthesis of avenaciolide 126 [104,105]. 

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