Alkyne derivatives insertion

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

Benzyne, which is generated in situ from 2-(trimethylsilyl)phenyl triflate and KF, acts as an alkyne congener in distannation in the presence of palladium-/ r/-alkyl isocyanide complex.157 A variety of substituted benzyne derivatives inserts into the Sn-Sn bond to give l,2-bis(stannyl)benzenes (Equation (59)). The reaction fails to occur in the presence of other palladium catalysts such as Pd(PPh3)4. 

Acylzirconocene chloride derivatives are easily accessible in a one-pot procedure through the hydrozirconation of alkene or alkyne derivatives with zirconocene chloride hydride (Schwartz reagent) [Cp2Zr(H)Cl, Cp = cyclopentadienyl] and subsequent insertion of carbon monoxide (CO) into the alkyl— or alkenyl—zirconium bond under atmospheric pressure (Scheme 5.1) [2],... 

In an alternative strategy functionalized phenols, such as iodophenol, were involved in palladium-catalyzed carbonylation of alkynes or allenes, producing coumarin or chromone derivatives (Scheme 23) [130-133]. After oxidative addition of the iodoarene to the Pd(0) catalyst the order of insertion of either CO or the unsaturated substrate mainly depends on the nature of the substrate. In fact, Alper et al. reported that CO insertion occurs prior to allene insertion leading to methylene- or vinyl-benzopyranone derivatives [130]. On the contrary, insertion of alkynes precedes insertion of CO, affording couma-rine derivatives, as reported by Larock et al. According to the authors, this unusual selectivity can be explained by the inability of the acyl palladium species to further react with the alkyne, hence the decarbonylation step occurs preferentially [131-133]. 

The polymerization of substituted alkynes is postulated to proceed either by the metathesis mechanism or by an insertion mechanism (18). Numerous alkyne derivates have been shown to polymerize in the presence of group V, VI, and VIII transition metal catalysts. 

Facile addition of either alcohols or amines to carbene complex 288 produces the / -am i n o-a, /i-unsaturated carbene complexes 289, which are useful for the preparation of cyclopentenone derivatives. Insertion of alkyne to 289 gives the 1,3-dienylcarbene complex 290, and its formal [3+2] cycloaddition gives cyclopentadiene 291. Under different conditions, [2+2+1] cycloaddition of vinylketene 292 produces the 5-methylene-2-cyclopentenone derivative 293 [88], The cyclopentenone 295, isomeric to 293, was obtained by the reaction of complex 294 with trimethylsilylacetylene, and oudenone (296) was synthesized by its hydrolysis [89]. 

Acylzirconocene chlorides are easily accessible in a one-pot procedure through the hydrozirconation see Hydrozirconation) of alkene or alkyne derivatives with the Schwartz s reagent and subsequent migratory insertion see Migratory Insertion) of carbon monoxide into the alkyl- or alkenyl zirconium bond. The stability of the acylzirconocene chlorides is remarkable at room temperature, and consequently allows many applications in organic synthesis. 

The use of Me3NO to induce substitution of dppm (bis(diphenylphosphino)-methane) for CO molecules on dinuclear iron complexes led to insertion of CO into C-C bonds of alkyne-derived metallacycles. Similar behavior was observed when [PPNJCl salts were used to favor the formation of alkyne-substituted triruthenium dppm-containing clusters.I This behavior should be compared with the insertion of CO into allenylidene and phosphido-bridging ligands occurring when dppm coordinates to binuclear ruthenium complexes as shown in Fig. 3. This reaction is a nucleophilic attack of the coordinated allenylidene and phosphido groups on a coordinated CO (see Section 2.8.2.2). 

Carboranes may contain one, two, three or four carbon atoms, although those with two have been most thoroughly studied, being readily accessible by the alkyne route. Insertion of ethyne into the arachno borane B Hj gives a mixtime of nido-carboranes including l,2-C2BjH, and alkyl derivatives of nido-2,3,4-CjBjH. Treatment of the former product with more ethyne affords closo-2, 3,4, 5-C,B,H, (Fig. 11.6). 

Alkyne either Inserts into the alkylidyne bridge of CFe2W(w2 CR) (u-CO)(C0)gCp3 (R = p-tol) to form a binuclear derivative or (e.g. alkyne = 02(811102)2 displaces two CO groups to form... 

Insertion of a ttvo-carbon unit into a five-membered metallacycle may afford formation of a six-membered carbocycle (Eq. 60), such as a benzene derivative via a formal [2+2+2] aromatization of three alkynes. Similarly, insertion of a C-X unit such as a nitrile into a five-membered metallacycle may afford formation of a six-membered heterocycle, such as a pyridine derivative (Eq. 60). In recent years, Takahashi laboratory and other laboratories have developed a number of synthetically useful methods for six-membered cyclic compounds by taking advantage of five-membered metallacycles of zirconocenes and ti-tanocenes [1-5]. 

The benzene derivative 409 is synthesized by the Pd-catalyzed reaction of the haloenyne 407 with alkynes. The intramolecular insertion of the internal alkyne, followed by the intermolecular coupling of the terminal alkyne using Pd(OAc)2, Ph3P, and Cul, affords the dienyne system 408, which cyclizes to the aromatic ring 409[281]. A similar cyclization of 410 with the terminal alkyne 411 to form benzene derivatives 412 and 413 without using Cul is explained by the successive intermolecular and intramolecuar insertions of the two triple bonds and the double bond[282]. The angularly bisannulated benzene derivative 415 is formed in one step by a totally intramolecular version of polycycli-zation of bromoenediyne 414[283,284],... 

Among several propargylic derivatives, the propargylic carbonates 3 were found to be the most reactive and they have been used most extensively because of their high reactivity[2,2a]. The allenylpalladium methoxide 4, formed as an intermediate in catalytic reactions of the methyl propargylic carbonate 3, undergoes two types of transformations. One is substitution of cr-bonded Pd. which proceeds by either insertion or transmetallation. The insertion of an alkene, for example, into the Pd—C cr-bond and elimination of/i-hydrogen affords the allenyl compound 5 (1.2,4-triene). Alkene and CO insertions are typical. The substitution of Pd methoxide with hard carbon nucleophiles or terminal alkynes in the presence of Cul takes place via transmetallation to yield the allenyl compound 6. By these reactions, various allenyl derivatives can be prepared. 

In 1986 Yamashida et al. found that the reaction of the (morpholino)phenyl-carbene complex 46 with symmetric alkynes 47 gave the morpholinylindene derivatives 48 and 49, as well as the indanones 50 derived from the latter by hydrolysis, in excellent yields (Scheme 9) [54]. This contrasts with the behavior of the corresponding (methoxy)phenylcarbene complex, which solely undergoes the Dotz reaction [55]. This transformation of the amino-substituted complex 46 apparently does not involve a CO insertion, which is an important feature of the Dotz benzannelation. 

Table 2 Formation of cyclopentadienyl derivatives 75 via transmetallated alkyne-inserted rhodium-carbene complexes (see Scheme 15)...

The insertion of alkynes into a chromium-carbon double bond is not restricted to Fischer alkenylcarbene complexes. Numerous transformations of this kind have been performed with simple alkylcarbene complexes, from which unstable a,/J-unsaturated carbene complexes were formed in situ, and in turn underwent further reactions in several different ways. For example, reaction of the 1-me-thoxyethylidene complex 6a with the conjugated enyne-ketimines and -ketones 131 afforded pyrrole [92] and furan 134 derivatives [93], respectively. The alkyne-inserted intermediate 132 apparently undergoes 671-electrocyclization and reductive elimination to afford enol ether 133, which yields the cycloaddition product 134 via a subsequent hydrolysis (Scheme 28). This transformation also demonstrates that Fischer carbene complexes are highly selective in their reactivity toward alkynes in the presence of other multiple bonds (Table 6). 

The insertion reaction between alkenylcarbene complexes and electron-rich alkynes such as 1-alkynylamines (ynamines) leads to mixtures of two regioi-someric cyclopentyl derivatives [78]. Thus, if the insertion occurs on the carbon-metal bond a new aminocarbene complex is produced which evolves to a cyclopentenylmetal derivative. On the other hand, if the insertion reaction occurs on the carbon=carbon double bond of the alkenyl complex, the reaction gives a l-metala-4-amino-l,3,5-triene complex which finally generates a different regioisomer of the cyclopentenylmetal derivative (Scheme 31). 

The reaction of alkenylcarbene complexes and alkynes in the presence of Ni(0) leads to cycloheptatriene derivatives in a process which can be considered as a [3C+2S+2S] cycloaddition reaction [125]. As shown in Scheme 77, two molecules of the alkyne and one molecule of the carbene complex are involved in the formation of the cycloheptatriene. This reaction is supposed to proceed through the initial formation of a nickel alkenylcarbene complex. A subsequent double regioselective alkyne insertion produces a new nickel carbene complex, which evolves by an intramolecular cycloprop anation reaction to form a nor-caradiene intermediate. These species easily isomerise to the observed cycloheptatriene derivatives (Scheme 77). 

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