Synthesis of Terminal Olefins

Since one or the other of the C-1 fragments generated by both disconnections are usually commercially available (i.e. MeS02Ph or HCHO), the choice of path a or 

Condensation of sulfone-derived anions with ketones - including enolizable ketones - can also be brought to fruition. It must be noted, however, that in reaction 3.10 [25], some 15% of starting material 38 is recovered, probably originating from competitive deprotonation of the highly acidic a-keto hydrogen. Good 1,2-diastereocontrol is also exercised in this case. 

At the outset, it should be noted that the original Julia olefination protocol is mostly usefiil in the synthesis of ( )-olefins. Depending upon the conditions of the reductive eUmination, the E/Z selectivity can be modulated, but in general ( )-alkenes are usually easier to obtain than their (Z)-counterparts. This stereochemical control - which also arises in the preparation of tri- and tetrasubstituted olefins - will be discussed in greater detail in the section on reductive elimination (Section 3.4). 

Furthermore, trapping of the in situ generated alkoxide - usually with AC2O, 

Another serious problem that can be encountered when reacting an a-sulfonyl anion with an aldehyde is competitive enolization of the carbonyl derivative, which can sometimes lead to large amounts of recovered starting material. It has been shown that judicious choice of the appropriate solvent may be a key factor for success [51]. As indicated in Table 3.1, using DME instead of THF suppresses the undesirable enolization almost completely. Whilst DME appears to be especially effective in the case of linear, aliphatic aldehydes (entries 1 and 2), THF seems to be preferred when a-substituted aldehydes are employed as coupling partners (entry 3). 

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Synthesis of terminal olefine from ketones or esters via a Ti methylene transfer reagent. 

Terminal aikenes. /8-Silyl sulfones on treatment with fluoride ion undergo elimination to the corresponding alkene. This reaction, coupled with a -alkylation of sulfones, is useful for synthesis of terminal olefins and 1,3-dienes. 

Najera s methyl BTFP sulfone 319 has been applied in the synthesis of terminal olefins [106] (Scheme 103, cf Scheme 78 and the relevant text). Reaction of 319 (1 molar equivalent) with aldehydes or ketones (1.1 molar equivalent) could be conveniently carried out using P4-f-Bu (1.2 molar equivalent) or KOH-TBAB (9 molar equivalent) imder Barbier conditions. Some examples are shown in Table 25. 

Methylselenoxy analogs are even more difficult to react and treatment of the corresponding methylseleno derivative at 80 °C with terf-butyl hydroperoxide/basic alumina (conditions which proved particularly efficient for the synthesis of terminal olefins from methyl selenides bearing a methylseleno group at the terminus of the alkyl chain 7,8,12>, which are more difficult to react) as expected 140) does not lead 35) to the desired alkylidene cyclopropanes but to low yields of cyclobutanones resulting probably from the well-known 140) reaction of rert-butyl hydroperoxide with the alkylidene cyclopropane formed transiently35). 

CLIVE-REICH-SHARPLESS Olefination Organoselenium compounds in synthesis of terminal olefins, unsaturated ketones... 

The recently discovered reaction880 of methylene dibromide or diiodide with carbonyl compounds in the presence of magnesium amalgam provides an extremely simple synthesis of terminal olefins ... 

A convenient synthesis of terminal olefins, which may complement the Wittig reaction, has been reported. The procedure (Scheme 6) involves the addition of a... 

The reaction of alkenyldi-isobutylalane with titanocene dichloride gives dimetalloalkanes (25), which convert ketones into olefins (26) in good yield (around 65%) but with only poor stereoselectivity the general use of heavy main-group elements in the synthesis of terminal olefins and of (Z)- and ( )-olefins stereospecifically has been reviewed by Kauffmann. ... 

A similar method has been developed by Seeberger et al. for metathesis reaction with pentene to give octene-substituted monosaccharide derivatives [373]. In previous solution phase experiments three catalysts were screened at different temperatures and in different solvents which suggest that metathesis proceeds best in dichloromethane at 0°C and with (H2lmes)(3-Br-py)2-(Cl)2Ru = CHPh] as the catalyst. AU soUd phase experiments have been performed on Merrifield octenediol linker 731 and have been checked for the cleavage reaction with ethylene as described in Scheme 109 for the synthesis of terminal olefins. 

Rhodium and cobalt carbonyls have long been known as thermally active hydroformylation catalysts. With thermal activation alone, however, they require higher temperatures and pressures than in the photocatalytic reaction. Iron carbonyl, on the other hand, is a poor hydroformylation catalyst at all temperatures under thermal activation. When irradiated under synthesis gas at 100 atm, the iron carbonyl catalyzes the hydroformylation of terminal olefins even at room temperatures, as was first discovered by P. Krusic. ESR studies suggested the formation of HFe9(C0) radicals as the active catalyst, /25, 26/. Our own results support this idea, 111,28/. Light is necessary to start the hydroformylation of 1-octene with the iron carbonyl catalyst. Once initiated, the reaction proceeds even in the... 

In addition to transition metals, recent work has demonstrated that strong Lewis acids will catalyze the addition of silanes to alkynes in both an intra- and an intermolecular fashion.14,14a-14c The formation of vinylsilanes from alkynes is possible by other means as well, such as the synthetically important and useful silylcupration15,15a of alkynes followed by cuprate protonation to afford vinylsilanes. These reactions provide products which can be complementary in nature to direct hydrometallation. Alternatively, modern metathesis catalysts have made possible direct vinylsilane synthesis from terminal olefins.16,16a... 

The greater reactivity of terminal olefins compared to their more hindered di-and tri-substituted counterparts became evident in the model studies (Sect. 2.2.1) and in the total synthesis of epothilones A, B and E (Sects. 2.2.2-2.2.4). Suitably positioned disubstituted olefins can, however, participate in RCM reactions employing the molybdenum initiator 1 [19], and this is demonstrated in the total synthesis of epothilone B (5) (Sect. 2.2.3). As expected this transformation proved impossible using the ruthenium complex 3. 

Recendy, we found that A -allyl-o-vii rlaniline 44 gave 1,2-dihydroquinoline 45 by normal RCM and developed silyl enol ether-ene metathesis for the novel synthesis of 4-siloxy-1,2-dihydroquinoline and demonstrated a convenient entry to quinolines and 1,2,3,4-tetrahydroquinoline [13], We also have found a novel selective isomerization of terminal olefin to give the corresponding enamide 46 using rathenium carbene catalyst [Ru] and silyl enol ether [14], which represented a new synthetic route to a series of substituted indoles 47 [12], We also succeeded an unambiguous characterization of mthenium hydride complex [RuH] with ACheterocyclic carbene... 

Synthesis of 2-[18F]fluoroalkyl (Et, Pr, But, pentyl and hexyl) spiperone derivatives, 306a-d, involved iodo[18F]fluorination of terminal olefins (equation 169) followed by... 

Recent examples of the first route have been described by Kobayashi and coworkers, who reported the synthesis and characterization of polymeric Pcs obtained through the olefin metathesis polymerization of terminal olefin groups in the side chains of unsymmetrical Pc monomers [159], X-ray analysis of the solid material indicates that the Pcs are ordered in stacks. 

Under salt-free conditions, the as -oxaphosphetanes formed from nonstabilized ylides can be kept from participating in the stereochemical drift and left intact until they decompose to give the olefin in the terminating step. This olefin is then a pure ds-isomer. In other words, salt-free Wittig reactions of nonstabilized ylides represent a stereoselective synthesis of ds-olefins. 

Oxo synthesis. Hydroformilation of a-olefins with CO and H2 is usually used for the synthesis of terminal oxygenated compounds (alcohols, aldehydes and carboxylic acids). 

Olefin synthesis. The preparation of olefins by decomposition of alkyl phenyl selenoxides (Diphenyl diselenide, 5, 272-276) is very useful, except in the case of primary alkyl phenyl selenoxides, which usually give low yields of terminal olefins on decomposition. However, the presence of electron-withdrawing substituents on the benzene ring increases both the rate of elimination and the yield of olefins. In instances where use of diphenyl diselenide results in low yields. Sharpless and Young recommend use of o-nitrophenyl selenocyanate (1) or 4,4 -dichlorodiphenyl diselenide, both of which are converted into the corresponding ArSe Na" reagents on reduction with sodium borohydride in ethanol. 

A new approach to construction of 3-aminosugar moieties by stereospecific intramolecular addition of a carbon-free radical to hydrazone 125 derived from crotonaldehyde was recently demonstrated by Friestad. This synthesis, comprising asymmetric dihydroxylation, PhS radical-induced C = N bond alkylation (C-vinylation) and subsequent Wacker oxidation [88] of terminal olefin 128, which afforded L-daunosaminide derivative 129, in overall 32% yield, is outlined in Scheme 23 [89]. 

Structure (ATO) gives a product distribution that is dominated by adipic acid. This is thought to result because the narrower channels inhibit the release of cyclohexanol and cyclohexanone and the reaction proceeds further to the more mobile linear products, such as adipic acid. Selectivity is also observed in the aerial oxidation of linear alkanes. If the reaction is performed over large-pore solids, w-alkanes are oxidised preferentially at carbon atoms at C2 and C3 positions in the chain, in accordance with the C-H bond strengths at these positions. If a small-pore structure such as CoAPO-18 is used, however, the product selectivity favours Cl oxyfunctionalised products. The synthesis of terminally oxidised alkanes would be of use for many applications, because linear terminal alcohols could be prepared from alkane feedstocks, rather than from a-olefins (via hydroformylation). 

Addition of anunonia and amines across the carbon-carbon double bond of alkenes was considered restricted to activated unsaturated compounds. However, some cases of addition to inactivated compounds in the presence of alkali metals at high temperatures and pressures had been found. More recently, using selective catalysts and in the presence of carbon monoxide (CO), hydroaminometh-ylation of terminal olefins has proven itself to be attractive for the synthesis of specific secondary and tertiary aliphatic amines (Equation 10.46, after Ahmed et al., 2003). 

Tsuji et al. have further exemplified the palladium(ii)-catalysed functionalization of terminal olefins into methyl ketones, in the synthesis of rethrolones, ° jasmonates ° (Scheme 27), and in a bisannelation sequence. The same group... 

The Wacker process has also been applied to the ketonization of terminal olefins. Although these applications are complicated by the isomerization of the olefins, good selectivities are now obtained in particular if DMF is added. The reaction is currently used in organic synthesis. 

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