Internal and Cyclic Olefins

The reaction rates of various types of olefins follow much the same pattern with both cobalt- and rhodium-catalyzed systems. Wender and co-workers (47) classified the nonfunctional substrates as straight-chain terminal, internal, branched terminal, branched internal, and cyclic olefins. The results they obtained are given in Table III. 

Hydrogenation of a olefines, as well as internal and cyclic olefines, is possible. However the catalyst is very sensitive to the olefin structure and, for example, tri-substituted ethylenic derivatives are hardly reduced. 

High yields and efficiency for H2O2 utilization were achieved for 3a-catalyzed epoxidation of various terminal, internal, and cyclic olefins (Eq. 4.4). For epoxidation of primary allylic alcohols, the corresponding epoxy alcohols were obtained selectively with small amounts of a,p-unsaturated aldehydes. 

There are perhaps more known W-based catalysts for olefin metathesis than all others together. Many studies have been made on the catalyst systems themselves in an attempt to elucidate the nature of the active species and its mode of formation. They are especially effective for internal and cyclic olefins. Many examples will be found throughout this book. Here we will illustrate some of the main types. 

AH the three tested colloidal dispersions exhibited roughly the same catalytic activity for hydrogenation of terminal olefins but differences were observed for internal and cyclic olefins. 

These. supramolecular catalysts showed high substrate selectivity in competition hydrogenation experiments and exceptional activity in the hydroformylation reactions. In contrast to the simple methylated P-cyclodextrin previously mentioned, even internal and cyclic olefins were converted into aldehydes. Such improvements were explained with the formation of an inclusion complex at the phase boundary, with the cylodextrin host fixing the substrate in the proximity of the catalytically active metal center (Fig. 

CHgtCRa (under UV irradiation) - MegSnCHaCHRa R Me, Et, (Me + MeaCH) (1955) Internal and cyclic olefins (under UV Irradiation) adducts from (MeCH )a > MeCH CHEt, MeCHtCMea, indene, c.CsHe, c.CeHio, l-MeCeHg, Or xs (1955) l,3-C6HgCN (1953). 

Internal olefins and cyclic olefins also react with methylphenylsilylene to give silyl-substituted olefins. Irradiation of 10 with a high-pressure mercury lamp in the presence of cis-2-butene in hexene yields 3-methylphenylsilyl-l-butene in 29% yield. Small amounts of the photoisomer 1-methyl-... 

Tsonis and Farona found Re(CO)sCl/EtAlCl2 active at 110°C for homo-polymerization of cyclic compounds containing 5-, 6-, 7-, and 8-membered rings to low-molecular-weight totally saturated materials (ring systems preserved). The initial active form of the catalyst is [(CO)4Re=CHEt ], the same as for the metathesis of internal and terminal olefins." ... 

An efficient isomerization of aliphatic and cyclic olefins is achieved using well-defined bis-Cp alkyne titanium complexes as catalysts. These complexes isomerize 1-alkenes to internal alkenes under mild conditions. The titanium complex can be recovered quantitatively. Cyclic olefins, for example, cyclohexadienes, also undergo... 

MODEL STUDIES Early in this study it appeared that [2.2.1]bicyclic olefin resins added conventional crosslinking thiols in a rapid, exothermic, manner. These results appear to contradict earlier reports that internal olefins and cyclic olefins such as cyclohexene and cydopentene react only slowly with thiols. In reality, [2.2.1]bicydic olefins represent a separate dass of reactive olefins. These results are also consistent with reports (16-19) that bicyclic olefins such as norbomadiene are quite reactive to the addition of monofunctional thiols and thiyl radicals. In order to quantify the relative reactivity of norbornene resins with other "standard" ene components, a model study of the addition reaction was undertaken. A "typical" thiol (ethyl mercaptoacetate) was examined in a series of competitive reactions in which there was a defidency of olefin (Figure 4). Olefin substrates that were compared were norbornene, styrene, butyl vinyl ether, [2.2.2]bicydooctene and phenyl allyl ether. The results of that study are listed below in Table I. 

The ( )-alkyne complexes were also synthesized by the reaction of 7 with internal alkynes and cyclic olefins. Such perpendicular coordination of the alkyne ligand to one of the M-M bonds of the ttimetallic cluster is characteristic of the complex adopting a 46-electron configuration, while the alkyne ligand is coordinated parallel to the M-M bond for the 48-electron complexes. The (T)-cyclohexyne complex 53e rearranged to a coordinatively saturated /t3- 7 ( )-cyclohexyne complex upon treatment with 1 atm of CO. 

Cyclometalated catalyst 9 was shown to be effective in the Z-selective ethenolysis of internal olefins (Scheme 8) at relatively low catalyst loadings (0.5 mol%) and ethylene pressures (1-5 atm) [51, 53]. /Z-olefin mixtures were successfully enriched to the pure E-isomer products, with accompanying formation of terminal olefins derived from the Z-isomer. This process was demonstrated to be effective for both linear and cyclic olefins and was found to be tolerant of a number of functional groups including esters, alcohols, amines, and ketones. Reactions were generally conducted at 35°C, which was found to provide an optimal balance with respect to yield and reaction time. Although the reaction is more rapid at... 

Abnormal imidazolylidene ruthenium complex 45 was developed by Bera and co orkers for the NaI04-mediated oxidation of olefins as a mild alternative to ozonolysis [eqn (3.9)]. For example, styrene was oxidized to benzaldehyde quantitatively in half an hour at room temperature with only 1 mol% 45. Internal olefins were oxidized very efficiendy as well, and cyclic olefins such as cyclohexene afforded a,o)-dialdehydes in excellent yields. Traces of over-oxidation to the corresponding carboxylic acids were only observed with aliphatic olefins. Also,... 

Some significant observations can be made from these results. Straight-chain terminal olefins are the most reactive. Little if any difference exists between 2- and 3-internal, linear olefins. Branching is important only if present at one or more of the olefinic carbon atoms reaction becomes more difficult as branching increases. Cyclic olefins react in an irregular fashion, but all are less reactive than terminal, linear olefins. 

The intramolecular process has been proposed by Widenhoefer with palladium(ll) catalysts.40 41 Cyclization of alkenyl-1,3-dione 26 proceeds efficiently with commercially available palladium species in dioxane at room temperature (Scheme 8). Such mild conditions allow high tolerance vis-a-vis functionalities, and cyclic products are obtained in good yields. Cyclization, tolerated substitution at the terminal methyl group and at the active methylene. This protocol also allows the reaction of internal olefins with (Z)- or ( )-configuration to occur. 

The synthesis of succinic acid derivatives, /3-alkoxy esters, and a,j3-unsaturated esters from olefins by palladium catalyzed carbonylation reactions in alcohol have been reported (24, 25, 26, 27), but full experimental details of the syntheses are incomplete and in most cases the yields of yS-alkoxy ester and diester products are low. A similar reaction employing stoichiometric amounts of palladium (II) has also been reported (28). In order to explore the scope of this reaction for the syntheses of yS-alkoxy esters and succinic acid derivatives, representative cyclic and acyclic olefins were carbonylated under these same conditions (Table I). The reactions were carried out in methanol at room temperature using catalytic amounts of palladium (II) chloride and stoichiometric amounts of copper (II) chloride under 2 atm of carbon monoxide. The methoxypalladation reaction of 1-pentene affords a good conversion (55% ) of olefin to methyl 3-methoxyhexanoate, the product of Markov-nikov addition. In the carbonylation of other 1-olefins, f3-methoxy methyl esters were obtained in high yields however, substitution of a methyl group on the double bond reduced the yield of ester markedly. For example, the carbonylation of 2-methyl-l-butene afforded < 10% yield of methyl 3-methyl-3-methoxypentanoate. This suggests that unsubstituted 1-olefins may be preferentially carbonylated in the presence of substituted 1-olefins or internal olefins. The reactivities of the olefins fall in the order RCH =CHo ]> ci -RCH=CHR > trans-RCH =CHR >... 

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