Olefin unactivated

The RuCl4 system is only an effective catalyst for the hydrogenation of activated olefins. Unactivated olefins form ruthenium adducts, but are not hydrogenated. 

Ene acceptors can be divided into three classes olefinic, unactivated olefinic, activated by conjugation with electron withdrawing groups and acetylenic. Examples of each class are listed in the Tables. 

Addition of HCN to unsaturated compounds is often the easiest and most economical method of making organonitnles. An early synthesis of acrylonitrile involved the addition of HCN to acetylene. The addition of HCN to aldehydes and ketones is readily accompHshed with simple base catalysis, as is the addition of HCN to activated olefins (Michael addition). However, the addition of HCN to unactivated olefins and the regioselective addition to dienes is best accompHshed with a transition-metal catalyst, as illustrated by DuPont s adiponitrile process (6—9). 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

Harano and colleagues [48] found that the reactivity of the Diels-Alder reaction of cyclopentadienones with unactivated olefins is enhanced in phenolic solvents. Scheme 6.28 gives some examples of the cycloadditions of 2,5-bis-(methoxycar-bonyl)-3,4-diphenylcyclopentadienone 45 with styrene and cyclohexene in p-chlorophenol (PCP). Notice the result of the cycloaddition of cyclohexene which is known to be a very unreactive dienophile in PCP at 80 °C the reaction works, while no Diels-Alder adduct was obtained in benzene. PCP also favors the decarbonylation of the adduct, generating a new conjugated dienic system, and therefore a subsequent Diels-Alder reaction is possible. Thus, the thermolysis at 170 °C for 10 h of Diels-Alder adduct 47, which comes from the cycloaddition of 45 with 1,5-octadiene 46 (Scheme 6.29), gives the multiple Diels-Alder adduct 49 via decarbonylated adduct 48. In PCP, the reaction occurs at a temperature about 50 °C lower than when performed without solvent, and product 49 is obtained by a one-pot procedure in good yield. 

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. 

Organotin hydrides can also be added to unactivated olefinic (without an electron-withdrawing group on one carbon) bonds provided the reaction is initiated by UV radiation, AIBN or y-rays113-116. In one instance, an organotin hydride has even been added to an unactivated olefin without an initiator. This unexpected addition reaction occurred at high pressure117. 

Organotin hydrides add across carbon-carbon triple bonds even more easily than they add across carbon-carbon double bonds. For example, the addition to the unactivated C=C bond of phenylacetylene proceeds spontaneously at 20 °C without an initiator (equation 88), whereas the addition to an unactivated olefin requires the presence of an initiator118. 

A closely related dicationic platinum complex has been shown to transform efficiently /3-citronellene into cis-thujane in a highly diastereoselective manner, which mimics terpene biosynthesis.362 Also, using platinum(n) catalysis, Widenhoefer has reported an intramolecular alkylation of indoles with unactivated olefins, which can be carried out in an enantioselective fashion (Scheme 99).363... 

Reductive Cyclization of Unactivated Olefinic Carbonyl Compounds 517... 

In general, transition metal-catalyzed addition reactions to 1,3-dienes gave 1,4-adducts via 7t-allyl metal intermediates.23 The ar //-Markovnikov 1,2-addition mode of this reaction is therefore unusual (Scheme 17). It was noted that the configuration of the 3-olefin was retained with either ( )- or (Z)-1,3-dienes. The observation that the 3-olefin was unimportant for this reaction strongly suggests that the method could be applicable to unactivated alkenes. 

Some diazoalkanes cyclopropanate olefins in the absence of any catalyst [658-660]. Thus, for instance, upon generation from A -cyclopropyl-A -nitrosourea at 0 °C diazocyclopropane spontaneously cyclopropanates methylenecyclopropanes [658]. Thermal, uncatalyzed cyclopropanations of unactivated olefines with aryldiazome-thanes can already occur at only slightly elevated temperatures (e.g. at 80 °C with 1-naphthyldiazomethane [661]). Henee, for enantioselective cyclopropanations with a chiral catalyst, low reaction temperatures should be chosen to minimize product formation via the uncatalyzed pathway. 

Rhodium catalysis has played a critical role in the development of this type of reaction. The rhodium-mediated [4 + 2] carbocyclization between dienes and unactivated olefins or alkynes is a notable early example of this concept [2]. Further investigations demonstrated the extension of this methodology to the reaction between a diene and an allene [3]. Expansion of the scope of this strategy, to both the intra- and intermolecular [5-1-2] homologs of the Diels-Alder reaction, was accomplished with a vinylcyclopropane and either an alkyne or an olefin to afford the carbocyclization adducts (Scheme 11.1) [4, 5]. 

Et3N unquestionably played an important role. In the presence of 0.5 molar equivalent of this amine, endoxide 55 was reduced by low-valent titanium reagent (molar ratio of endoxide TiCl LiAlH4 EtjN = 1 6.9 2.7 0.5) to a mixture of products, namely endo,cis-9S and trans-95 in a ratio of 1 5 (Scheme 20). In many cases, this reducing system would reduce enedicarboxylates to succinates, while other unactivated olefinic functionalities in the molecules would remain intact. A fitting example was the convCTsion of 96 to 97 as shown in Scheme 20. ... 

Alternative doubly and singly activated olefinic dipolarophiles also underwent cycloaddition, generating the products 47-49 in 27-61% yields, although attempted use of an ot,p-unsaturated ketone furnished 50 in only 8% yield, while unactivated dipolarophiles were unreactive (Fig. 3.4). 

Hosokawa, Murahashi, and coworkers demonstrated the ability of Pd" to catalyze the oxidative conjugate addition of amide and carbamate nucleophiles to electron-deficient alkenes (Eq. 42) [177]. Approximately 10 years later, Stahl and coworkers discovered that Pd-catalyzed oxidative amination of styrene proceeds with either Markovnikov or anti-Markovnikov regioselectivity. The preferred isomer is dictated by the presence or absence of a Bronsted base (e.g., triethylamine or acetate), respectively (Scheme 12) [178,179]. Both of these reaction classes employ O2 as the stoichiometric oxidant, but optimal conditions include a copper cocatalyst. More recently, Stahl and coworkers found that the oxidative amination of unactivated alkyl olefins proceeds most effectively in the absence of a copper cocatalyst (Eq. 43) [180]. In the presence of 5mol% CUCI2, significant alkene amination is observed, but the product consists of a complicated isomeric mixture arising from migration of the double bond into thermodynamically more stable internal positions. 

Although the presence of an appropriately located heteroatom seemed to be required for the success of the allylzincation, it is in fact not necessary. Actually, one of the first reports of allylzincation of an unactivated olefin was related to an observed dimerization reaction when a solution of allylzinc bromide was heated at reflux (following its preparation from allyl bromide and metallic zinc in THF) or if reaction with an electrophile required... 

By contrast with the above examples which involve activated olefins, the addition of zinc enolates to unactivated alkenes is much more difficult to achieve. Although ethylene seems to be an acceptable partner for such additions, the reactions have to be carried out under pressure and require relatively long reaction times. Thus, the butylzinc aza-enolate generated from the SAMP hydrazone of cyclohexanone 452 reacted slowly with ethylene... 

An extension of the carbozincation of unactivated olefins by zinc enamides was recently reported and opened a new efficient entry to -alkylated ketones, especially those bearing an -secondary or tertiary alkyl group289. Indeed, such substrates are difficult to obtain by the conventional method relying on the alkylation of metal enamides or enolates... 

Using in situ prepared [AuOTfPPh3] as catalyst and relatively mild conditions, He and Yang obtained the first intramolecular addition to terminal alkenes [54]. Phenols and carboxylates were the nucleophiles chosen and several types of olefins, even unactivated ones, worked well in the reaction. In this study, the aforementioned authors also discovered gold s capacity for the constitutional isomerization of olefins, as demonstrated by the obtainment of the two isomers shown in Equation 8.16. 

Ethylene is the template for olefin reactions, but ethylene itself is rather unreactive, undergoing electrophilic attack by moderately strong Lewis acids. Nucleophilic attack on the bond even by the strongest Lewis bases has not been reported. The following sequence involves intramolecular addition of a carbanion to an unactivated olefin [111, 112]. The reaction is undoubtedly facilitated by active participation of the lithium cation as a Lewis acid [113]. 

Allenes926 and ketenes927 react with activated olefins and alkynes. Ketenes give 1,2 addition, even with conjugated dienes.928 Ketenes also add to unactivated olefins if sufficiently long reaction times are used.929 Allenes and ketenes also add to each other.930... 

This reaction is reversible and suitable p-hydroxy olefins can be cleaved by heat (7-43). There is evidence that the cleavage reaction occurs by a cyclic mechanism (p. 1043), and, by the principle of microscopic reversibility, the addition mechanism should be cyclic too.719 Note that this reaction is an oxygen analog of the ene synthesis (5-16). This reaction can also be done with unactivated aldehydes7211 and ketones721 if Lewis-acid catalysts such as... 

Aryl azides react with olefins to give 1,2,3-A2-triazolines.201-203 Whereas unactivated olefins are sluggish toward aryl azides, strained bicyclic systems, on the contrary, are particularly reactive.204-208 The rate of phenyl azide addition to a series of olefins parallels the heat of hydrogenation (Table Vffl).107 This thermodynamic parameter is a measure for the degree of strain associated with these molecules.200 Bicyclo[2.2.1]hep-tenes, such as norbomene (37), react readily at room temperature, and the addition occurs at the less hindered exo side (39).,06 1°7 210 211 A striking example of the increased... 

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