Acyclic Internal Olefins

The AHF of propanoids plays an important role in the framework of flavors and fragrances, and therefore most results are discussed in Section 6.I.3.5. Here, only some results will be exemplarily presented. 

A conversion of 20% at a TON = 355 h was reported with the (S,S,S)-Bisdiazaphos catalyst and stilbene as substrate. The chiral aldehyde was formed with 93% ee [30]. 

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The various modes of bonding that have been observed for alkenes to the trinuclear osmium clusters are shown in Fig. 7 [see (88)]. The simple 77-bonded structure (a) is relatively unstable and readily converts to (c) the vinyl intermediate (b) is obtained by interaction of alkene with H2Os3(CO)10 and also readily converts to (c) on warming. Direct reaction of ethylene with Os3(CO)12 produces (c), which is considered to be formed via the sequence (a) — (b) — (c) and (d). Both isomers (c) and (d) are observed and involve metal-hydrogen and metal-carbon bond formation at the expense of carbon-hydrogen bonds. In the reaction of Os3(CO)12 with C2H4, the complex 112088(00)902112, (c), is formed in preference to (d). Acyclic internal olefins also react with the carbonyl, with isomerization, to yield a structure related to (c). Structure (c) is... 

Cycloolefins, unlike acyclic internal olefins, undergo coordination polymerisation owing to the presence of ring strain. Loss of ring strain is an important contribution to the driving force of this polymerisation. 

Metathesis of Cycloolefins. The same general catalysts which promote the ring-opening polymerization of cycloolefins are also effective in the olefin metathesis reaction in which acyclic internal olefins undergo a unique redistribution process (1, 2, 5, 6). 

Acyclic internal olefins such as cis- and /raar-2-butene can be polymerized using Brookhart-type Ni(ll) and Pd(ll) complexes430 but in the absence of isomerization do not homopolymerize using Ziegler-Natta catalysts, although examples of co-polymerizations of ethylene with an internal olefin are known.313... 

STUDY OF THE ACTIVITY AND STEREOSELECTIVITY OF SOME METATHESIS CATALYSTS WITH ACYCLIC INTERNAL OLEFINS... 

A related complex, Mo(N-t-Bu)(CH-t-Bu)(OCMe(CF3)2)2 (10), was synthesized by Osborn et al. and investigated for the ROMP of norbomene and acyclic internal olefins [146]. Boncella performed metathesis reactions using tris(pyrazolyl)borate stabilized molybdenum complexes in combination with AIQ3 [147]. 

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 >... 

The results of the hydroformylation of internal olefins are reported in Table 9. In the case of (Z)- and (E)-2-butene, the same fare of the unsaturated carbon atom is formylated with either a rhodium- or platinum (—)-DIOP-containing catalytic system. With the rhodium catalyst, when an acyclic olefin is used as the substrate, the same fare is always attacked, and it is only the notation but not the geometric requirement that is different for (E)-l-phenyl-1-propene. The only exception is represented by bicyclo[2,2,l]heptene. However, using (—)-CHIRAPHOS instead of (—)-DIOP, also bieyelo[2,2,l]heptene behaves like internal butenes. No regularity is observed for the cobalt or ruthenium (—)-DIOP catalytic systems. With the same system, only in 3 cases out of 15 the face of the prochiral atom preferentially formylated has different geometric requirements. 

The effectiveness of acyclic olefins in reducing the MW depends very much on their structure and on the catalyst system, especially on the cis content of the polymer formed. The order of effectiveness of M2 in reducing the MW is generally RCH=CH2 > R CH=CHR (cw) > R CH=CHRV ) > R R C=CH2. An example of the comparative effectiveness of terminal and internal olefins is shown in Fig. 15.4. 

Asymmetric hydroboration of internal olefins was developed by Perez, Fernandez and co-workers,with [B(pin)]2 as boration reagent. Ligands 126 provided the best chiral induction (up to 59% ee) (Scheme 13.6). Improved results were obtained by Hoveyda and co-workers using 127 and 128 with acyclic and cyclic internal alkenes. 

Apart from cross-metathesis, ROMP, and RCM, there are other less common metathesis reactions. These are acyclic diene metathesis polymerization (ADMET), ring-opening cross-metathesis (ROCM), ring-rearrangement metathesis (RRM), and ethenolysis. A general ADMET reaction is shown by reaction 7.3.1.7. ADMET reactions are generally performed on a,well-defined and strictly linear polymers with unsaturated polyethylene backbones. Ethenolysis is the cross-metathesis of ethylene with an internal olefin. 

To avoid oligomer formation, Roberts and Rainier utilized an internal rather than a terminal olefin as a precursor to the cychzation reaction (Scheme 3.57) [62]. To this goal, internal olefin 303 was synthesized and subjected to enol ether formation but with the titanium efhylidene rather than the methylidene reagent for the acyclic enol ether forming reaction. Surprisingly, this relatively minor modification resulted in the conversion of 303 into cyclic enol ether 300 [63]. No acyclic enol ether was observed. The authors argued that the relatively moderate yield was due to the instability of the products and was not necessarily a result of an inefficient reaction. 

Bishop and Hamer found that acyclic a,/8-unsaturated 1,2-diketones form cyclopentanol derivatives in high yield, while / ,y-unsaturated derivatives form oxetanes by internal cycloaddition.114 Unexpectedly, the y,S-unsatu-rated derivatives also gave oxetanes after an initial migration of the double bond to the /8,y position. The formation of oxetanes such as 38 was observed in the camphorquinone sensitized dimerization of butadiene.115 Photocycloadditions of a-diketones to various olefins have been studied by several groups.116... 

All types of olefins can serve as substrates. Suitable acyclic olefins include ethylene, terminal and internal monoenes up to and including tetrasubstituted-double bonds, and aryl-substituted olefins. With dienes (and polyenes) an additional, intramolecular reaction pathway becomes available which leads to cyclic olefins (Reaction 2). 

Organoboranes derived from internal acyclic olefins by hydroboration with BH3 undergo thermal isomerization at elevated temperature (100-160 °C). The Boron atom readily moves down the chain, past a single branch, but not past a quaternary carbon atom [1]. 

The fact that internal acyclic olefins are unreactive toward aerobic epoxidation would suggest that peracetic acid is not formed according to Eq. (6.15). 

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