Terminal double bond, activity

The method was applied to the synthesis of (-t-)-l9-nortestosterone by the following sequence of reactions. Michael addition of the bisannulation reagent 124 to the optically active keto ester 129 and decarboxylation afforded 130, and subsequent aldol condensation gave 131. Selective Pd-catalyzed oxidation of the terminal double bond afforded the diketone 132 in 78% yield. Reduction of the double bond and aldol condensation gave ( + )-19-nortestosterone (133)[114]. 

The terminal double bond is active with respect to polymerisation, whereas the internal unsaturation remains in the resulting terpolymer as a pendent location for sulfur vulcanisation. The polymer is poly(ethylene- (9-prop5iene- (9-l,4-hexadiene) [25038-37-3]. 

Boelhouwer s discovery (23) prompted a flurry of activity in this area. Baker applied the Boelhouwer catalyst to the metathesis of w-olefinic esters (88). At an ester/W molar ratio of 20/1 (68°C), symmetrical olefinic diesters were formed in 34-36% yields with concomitant elimination of ethylene. In addition, Baker identified products recovered in 3-8% yield corresponding to addition of HC1 across the terminal double bond. 

Donor- and acceptor-substituted allenes with general structures 1 or 2 (Scheme 8.1) have the most obvious synthetic potential among functionalized allene derivatives and therefore they serve as versatile building blocks in many synthetic endeavors [1], As expected, the reactivity of the double bonds of 1 or 2, which are directly connected to the activating substituents, are strongly influenced by these groups. Hence there is enol ether or enamine reactivity of 1 and Michael acceptor type chemistry of 2. In addition, the terminal double bonds are also influenced by these functional groups. 

As mentioned above, the reactivity of alkoxyallenes is governed by the influence of the ether function, which leads to the expected attack of electrophiles at the central carbon C-2 of the cumulene. However, the alkoxy group also activates the terminal double bond by its hyperconjugative electron-withdrawing effect and makes C-3 accessible for reactions with nucleophiles (Scheme 8.3). This feature is of particular importance for cyclizations leading to a variety of heterocyclic products. The relatively high CH-acidity at C-l of alkoxyallenes allows smooth lithiation and subsequent reaction with a variety of electrophiles. In certain cases, deprotonation at C-3 can also be achieved. 

Propene- and butene-oligomers are complex mixtures. A typical isomer distribution is shown in Fig. 24. According to the thermodynamical stability the double bonds are distributed along the chain, terminal double bonds are present only in traces. To get predominant terminal products, a catalyst must provide extremely fast terminal hydroformylation activity for the traces of terminal olefins, a high isomerization activity to supply the terminal double bonds as fast as they are consumed, and low hydroformylation activity for internal double bonds. 

The active hydrogen atom in the donor molecule is the one which is attached to a terminal double-bonded carbon atom or to that double-bonded carbon to which the smaller alkyl group is attached. Thus, the active hydrogens in the following alkenes are indicated by asterisks ... 

Rule A. Olefins having a terminal double bond (e.g., 1-butene) are less stable than straight chain olefins having an internal double bond (e.g., 2-butene) and tend to yield a latter type under the influence of heat, catalyst, and other methods of activation (Whitmore and Herndon, 65 Whitmore and Homeyer, 44). 

Activity is largely retained in a compound in which one of the terminal double bonds in the side chain of tretinoin is replaced by an aromatic ring. The key reaction in the constmction of this compound consists in Wittig condensation of the ylide from... 

The analogous behaviour of PdQ2 and Pd/C is further demonstrated by the reactivity of allylic ethers of various nature (Table 3). In the carbonylation of l-methoxy-3-octene, the generation and the stabilization of the Pd(0) active species are more difficult than in the case [(T 3-C4H7)PdCl)2 and Pd(dba)2. The stability of this zerovalent species is also important in the carbonylation of cis and trans methoxycrotyle. Actually, for all such ethers, there is no extra-stabilization as observed with 1 and 2, where the terminal double bond could be coordinated to the metal centre (ref. 6). 

Instability of the polymer is responsible for the primary step in decomposition and is attributed either to fragments of initiator or to branched chains or to terminal double bonds. The appearance of branching is the result of reactions of chain transfer through the polymer, while that of unsaturated terminal groups results from reaction of disproportionation and chain transfer through the monomer. During thermal and thermo-oxidative dehydrochlorination of PVC, allyl activation of the chlorine atoms next to the double bonds occurs. In this volume, Klemchuk describes the kinetics of PVC degradation based on experiments with allylic chloride as a model substance. He observed that thermal stabilizers replace the allylic chlorine at a faster ratio than the decomposition rate of the allylic chloride. 

The formation of these compounds may be explained by the following transformations. The weakly nucleophilic hexamethyldisilazane initially reacts at the carbon atom of the multiple bond, and fluoride ion elimination takes place in the new zwitterion, forming a terminal double bond. Further catalysis by the fluoride ion generates an active N-nucleophile intramolecular cyclization involving the latter leads to a four-membered heterocycle. 

Further addition of the fluoride anion at the internal multiple bond generates hetero-anion F, which is involved in the intramolecular cyclization affecting the active terminal double bond. Stabilization of carbanion G occurs by fluoride ion elimination and formation of compound 129 having a multiple bond with a mobile fluoride atom. 

The reaction of an unsaturated compound with an antagonist function located at the end of a polymer chain is still the most commonly used method to synthesize macromonomers. We have already mentioned some processes that can be used to introduce into the chain end of a macromolecule a functional group, e.g. by deactivation of living carbanionic sites and transfer reactions of various kinds in cationic polymerization. We have also described some methods used to link an active terminal double bond to the chain end originally bearing hydroxy groups. 

Selectivity of the type found with ruthenium was not possible when palladium catalysts were used. For instance, hydrogenation of a mixture of 1- and 2-octene was completely nonselective over palladium catalysts. This lack of selectivity resulted from the high isomerization activity of palladium when the reaction was stopped at only one-tenth of completion, all 1-octene had disappeared by migration of the terminal double bond inward. 

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

Changing the transition-metal from palladium to rhodium (equation 62) makes possible, in addition to the straight-chain alkylation product (243), the regio- and stereoselective synthesis of amino acid derivatives with a terminal double bond (242), starting from optically active branched allylic substrates 241 (Table 21)" . Remarkably, the substitution products were obtained with high enantiomeric excesses, what might result from a slow isomerization of the intermediary formed allyl rhodium complexes ". 

Cyanide (method 388), sulfone, " or nitro compound," " The vinyl group in the alpha or gamma positions on the pyridine nucleus also "ndergoes this type of addition. " The activity of the labilizing group is trans- mitted to the terminal double bond of a vinylogous system. Thus, methyl vinylacrylate reacts with malonic ester as follows ... 

As more active members of the ruthenium catalyst family were developed, more complex systems could be prepared. For example, the first generation of ruthenium catalysts were very selective for less-substituted double bonds, and would not dose tri-substituted double bonds in medium-ring systems. As demonstrated below, Ru-1 would only react with the unsubstituted terminal double bond. However, the newer catalyst will convert the intermediate into the desired ring system containing a tri-substituted double bond (Eq. 6.5) [23]. 

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