Transition metal-catalyzed intramolecular

C—H bond 174-280,28i por comparison, only trace amounts of cyclopentane resulted from the CuS04-catalyzed decomposition of 1 -diazo-2-octanone or l-diazo-4,4-dimethyl-2-pentanone 277). It is obvious that the use of Rh2(OAc)4 considerably extends the scope of transition-metal catalyzed intramolecular C/H insertion, as it allows for the first time, efficient cyelization of ketocarbenoids derived from freely rotating, acyclic diazoketones. This cyelization reaction can also be highly diastereo-selective, as the exclusive formation of a m is-2,3-disubstituted cyclopentane carboxylate from 307 shows281 a). The stereoselection has been rationalized by... 

Transition Metal-Catalyzed Intramolecular Alder-Ene Reactions 568... 

The Alder-ene reaction has traditionally been performed under thermal conditions—generally at temperatures in excess of 200 °C. Transition metal catalysis not only maintains the attractive atom-economical feature of the Alder-ene reaction, but also allows for regiocontrol and, in many cases, stereoselectivity. A multitude of transition metal complexes has shown the ability to catalyze the intramolecular Alder-ene reaction. Each possesses a unique reactivity that is reflected in the diversity of carbocyclic and heterocyclic products accessible via the transition metal-catalyzed intramolecular Alder-ene reaction. Presumably for these reasons, investigation of the thermal Alder-ene reaction seems to have stopped almost completely. For example, more than 40 papers pertaining to the transition metal-catalyzed intramolecular Alder-ene reaction have been published over the last decade. In the process of writing this review, we encountered only three recent examples of the thermal intramolecular Alder-ene reaction, two of which were applications to the synthesis of biologically relevant compounds (see Section 10.12.6). 

Malacria and co-workers76 were the first to report the transition metal-catalyzed intramolecular cycloisomerization of allenynes in 1996. The cobalt-mediated process was presumed to proceed via a 7r-allyl intermediate (111, Scheme 22) following C-H activation. Alkyne insertion and reductive elimination give cross-conjugated triene 112 cobalt-catalyzed olefin isomerization of the Alder-ene product is presumed to be the mechanism by which 113 is formed. While exploring the cobalt(i)-catalyzed synthesis of steroidal skeletons, Malacria and co-workers77 observed the formation of Alder-ene product 115 from cis-114 (Equation (74)) in contrast, trans-114 underwent [2 + 2 + 2]-cyclization under identical conditions to form 116 (Equation (75)). 

C-N Ring-forming Reactions by Transition Metal-catalyzed Intramolecular Alkene Hydroamination... 

Transition metal-catalyzed intramolecular cyclization has also been applied to the formation of imidazoles. Palladium-mediated amino Heck reactions of 0-pentafluorobenzoylamidoximes 1163 afford l-benzyl-4-methylimid-azoles 1164 with a range of substituents at the 2-position. This method is particularly suitable for the preparation of imidazoles with a chiral substituent at the 2-position (Scheme 283) <20050L609>. 

The transition-metal-catalyzed intramolecular [5 + 2]-cycloaddition of 154 bearing a heteroatom between an alkynyl and a cyclopropylalkenyl group provides the heterocycles 155 bearing a seven-membered carbocycle (Scheme 53).129 Rhodium and ruthenium complexes have been used as catalysts of this [5 + 2]-cycloaddition. Trost and Shen extended this reaction for constructing the tricyclic heterocycle 157 from 156 (Scheme 54).129i... 

Transition-metal-catalyzed intramolecular reactions of carbon—carbon unsaturated compounds teth-... 

Intramolecular [3+2] cycloaddition reactions of unsaturated diazocarbonyl compounds as well as transition-metal-catalyzed intramolecular carbene-type reactions of diazo compounds constitute an important strategy in contemporary synthesis of alicyclic and heterocyclic systems [1]. In a program directed towards the synthesis of silaheterocycles according to this concept, we have used various silicon-functionalized (silyl)diazoacetates [2] as starting materials. In this communication, we report on the synthesis of silaheterocycles from a-(alkynyloxy)silyl-a-diazoacetates [3], which can be prepared easily by successive reaction of a silyl bis(triflate) with an alkyl diazoacetate and a propargyl alcohol [4],... 

Transition-metal-catalyzed intramolecular cycloisomerization is one of the most useful carbocyclization reactions, and specifically, the Rh-catalyzed cycloisomerization of 1,6-enynes provides a powerful tool in organic synthesis. Cyclization of l,6-en5me 452 catalyzed by Wilkinson s catalyst gave 1-exo-methylene-2-cyclohexene 453 via a 6-exo-trig mode in 83% yield (Scheme 2-50). Terminal substitution on the alkene moiety dramatically suppressed the cyclization, and substitution of the terminal alkyne moiety was detrimental to the reaction as well. 

SCHEME 21.48 Transition metal-catalyzed intramolecular hydroarylation of alkynes. 

Transition metal catalyzed intramolecular [4+2] diene-allene cycloadditions provide 6,6- and 6,5-fused ring systems in good yields under mild conditions. For example, from the tethered allene 404 in the presence of Ni(COD)2 as the catalyst a 97 % yield of the cycloadduct 405 is obtained resulting from addition to the terminal allene double bond. From the same substrate, using [Rh(COD)Cl]2 as the catalyst, the hydrindane derivative 406 is obtained in 90 % yield. 

Table 6.11 Transition metal catalyzed intramolecular [4+2] cycloadditions...

The transition-metal-catalyzed intramolecular hydroarylation of alkynes has emerged in recent years as a powerful tool for the atom-economical synthesis of carbocyclic and heterocyclic compotmds [101-104], including coiunarin derivatives [105-109]. In this context, Kitamura and coworkers have described the high-yield preparation of several angelicin derivatives 50 by intramolecular hydroarylation of 4-benzofuranyl alkynoates 49 using Pd(OAc)2 as catalyst (Scheme 23) [110]. The starting materials 49 are easily accessible substrates that can be generated by the condensation of... 

The intramolecular Diels-Alder reactions of yndienes can be accomplished utilizing various transition-metal catalysts, such as rhodium [21], nickel [21d,22], gold [23], iridium [24], and cobalt [25]. In many cases the transition-metal-catalyzed intramolecular Diels-Alder reactions rely on the Thorpe-Ingold effect to achieve good results. Typical examples for these transformations have been described for the synthesis of bicyclic products 39 and 40, respectively (Scheme 13.20) [21g,23b]. 

The transition metal-catalyzed intramolecular hydroalkoxylaticHi approach for the synthesis of spiroacetals has increased in popularity in the last decade. A variety of... 

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