Olefins scope

Ru complexes catalyze the reaction between 2-aryl pyridines and alkenyl esters (Scheme 23.16) [75]. These types of olefins are often only slowly reacting substrates in oxidative Heck (Fujiwara-Moritani) reactions [18] thus, their use in Ru-catalyzed C-H olefinations is a remarkable advance. The shown reaction is overall redox neutral and produces 1 equivalent of alcohol or acid as side product. A variety of heterocyclic directing groups can be employed, and many functional groups are tolerated. However, the olefin scope of the reaction is somewhat limited to alkyl- and aryl-substituted alkenes. 

In 2011, Bergman, EUman, and coworkers [55] reported the Rh(III)-catalyzed oxidative coupling of unactivated olefins via C-H activation. Until this publication appeared in the literature, most of the olefins used were activated, such as acrylates or styrenes. In this report, this team used aryl O-methyl oximes as substrates with unactivated olefins (Figure 4.25). Good olefin scope was demonstrated and the coupling reaction was always Iraws-selective for the di-substituted products. 

Palladium-catalyzed coupling reactions of organic halides with olefins or dienes (R. F. Heck, 1979) are broad in scope and simple to carry out. Anhydrous conditions or any special technique are not required and most functional groups are tolerated. 

Lithium aluminum hydride has also been shown to reduce vicinal dibromides to olefins efficiently, but the scope is limited by the reactivity of this reagent towards many functional groups. 

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

The mechanism of the Patemo-Biichi reaction is not well understood, and while a general pathway has been proposed and widely aceepted, it is apparent that it does not represent the full scope of reactions. Biichi originally proposed that the reaction occurred by light catalyzed stimulation of the carbonyl moiety 1 into an excited singlet state 4. Inter-system crossing then led to a triplet state diradical 5 which could be quenched by olefinic radical acceptors. Intermediate diradical 6 has been quenched or trapped by other radical acceptors and is generally felt to be on the reaction path of the large majority of Patemo-Biichi reactions. Diradical 6 then recombines to form product oxetane 3. 

Organocopper chemistry is still rapidly expanding its syntlietic scope. Hie scope of carbocupration, previously limited to acetylenes, has recently been extended to olefins [33-36]. 1,6-, 1,8-, 1,10-, and 1,12-Addition and 1,5-Su2" substitution reac-... 

Although beyond the scope of the present discussion, another key realization that has shaped the definition of click chemistry in recent years was that while olefins, through their selective oxidative functionalization, provide convenient access to reactive modules, the assembly of these energetic blocks into the final structures is best achieved through cydoaddition reactions involving carbon-het-eroatom bond formation, such as [l,3]-dipolar cydoadditions and hetero-Diels-Al-der reactions. The copper(i)-catalyzed cydoaddition of azides and terminal alkynes [5] is arguably the most powerful and reliable way to date to stitch a broad variety... 

The MT0/H202/pyridine system enjoys a broad substrate scope and has become the method of choice for the epoxidation of di-, tri-, and tetrasubstituted olefins. As an added benefit, it gives high diastereoselectivities for a number of cyclic dienes (Table 12.1). 

In the presence of a catalytic amount (10 %) of PTAB and anhydrous Chloramine-T (1.1 equiv.), a variety of olefins have been readily converted into the corresponding aziridines in acetonitrile at room temperature (Scheme 12.13). This method exhibits broad substrate scope, and the yields are usually high (Table 12.3) [42]. 

What we have shown here is the fact that large inverse values can be obtained for the Br2 addition to a "normal" olefin which should pass through a symmetrical, or nearly so, transition state. Of course, more work involving other systems would be beneficial in assessing the scope and limitation of the use of the a-deuterium kie s in mechanistic studies of Br2 and Br3 reactions with olefins. 

It was possible to effect lOOC reaction leading to six-membered rings, e.g., 220 in low yield (ca. 20%) by heating the reaction mixture at 110 °C (Eq. 22) [59]. In fact, Oppolzer and Keller [60] had previously reported the lOOC reaction of 219 to 220 in 20% yield by heating at 110 °C. Furthermore, the scope of these oxime-olefin cycloadditions has been extended to ketoximes, e.g., 221. The latter was prepared by amination of a-bromoacetophenone with allylamine 214a. Heating of 221 at 110 °C for 8 h led to cycloaddition with formation of the fused pyrrolidine 222 in 88% yield. As in Scheme 25, only one... 

Examination of the reactions of a wide variety of olefins with TTN in methanol (92) has revealed that in the majority of cases oxidative rearrangement is the predominant reaction course (cf. cyclohexene, Scheme 9). Further examples are shown in Scheme 18, and the scope and limitations of this procedure for the oxidative rearrangement of various classes of simple olefins to aldehydes and ketones have been defined. From the experimental point of view these reactions are extremely simple, and most of them are... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

Table 3 summarizes the scope and limitation of substrates for this hydrogenation. Complex 5 acts as a highly effective catalyst for functionalized olefins with unprotected amines (the order of activity tertiary > secondary primary), ethers, esters, fluorinated aryl groups, and others [27, 30]. However, in contrast to the reduction of a,p-unsaturated esters decomposition of 5 was observed when a,p-unsaturated ketones (e.g., trans-chalcone, trans-4-hexen-3-one, tra s-4-phenyl-3-buten-2-one, 2-cyclohexanone, carvone) were used (Fig. 3) [30],... 

By 1990, most of the catalytic reactions of TS-1 had been discovered. The wide scope of these reactions is shown in Fig. 6.1.35 Conversions include olefins and diolefins to epoxides,6,7 12 16 19 21 24 34 36 38 13 aromatic compounds to phenols,7,9 19 25 27 36 ketones to oximes,11 20 34 46 primary alcohols to aldehydes and then to acids, secondary alcohols to ketones,34-36 42 47-30 and alkanes to secondary and tertiary alcohols and ketones.6 34 43 31 52... 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

Besides ruthenium porphyrins (vide supra), several other ruthenium complexes were used as catalysts for asymmetric epoxidation and showed unique features 114,115 though enantioselectivity is moderate, some reactions are stereospecific and treats-olefins are better substrates for the epoxidation than are m-olcfins (Scheme 20).115 Epoxidation of conjugated olefins with the Ru (salen) (37) as catalyst was also found to proceed stereospecifically, with high enantioselectivity under photo-irradiation, irrespective of the olefmic substitution pattern (Scheme 21).116-118 Complex (37) itself is coordinatively saturated and catalytically inactive, but photo-irradiation promotes the dissociation of the apical nitrosyl ligand and makes the complex catalytically active. The wide scope of this epoxidation has been attributed to the unique structure of (37). Its salen ligand adopts a deeply folded and distorted conformation that allows the approach of an olefin of any substitution pattern to the intermediary oxo-Ru species.118 2,6-Dichloropyridine IV-oxide (DCPO) and tetramethylpyrazine /V. V -dioxide68 (TMPO) are oxidants of choice for this epoxidation. 

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