Carbenes reactions with diynes

Reactions of Fischer carbene complexes with diynes have been extensively studied as a synthetic approaches to alkynylarenes and biaryls. In general, Cr =C(0R )R (C0>5 (R = Me, Bu R = Ph, 1-nap, 1-cyclohexenyl) react with... 

Aryl- and alkenylcarbene complexes are known to react with alkynes through a [3C+2S+1C0] cycloaddition reaction to produce benzannulated compounds. This reaction, known as the Dotz reaction , is widely reviewed in Chap. Chromium-Templated Benzannulation Reactions , p. 123 of this book. However, simple alkyl-substituted carbene complexes react with excess of an alkyne (or with diynes) to produce a different benzannulated product which incorporates in its structure two molecules of the alkyne, a carbon monoxide ligand and the carbene carbon [128]. As referred to before, this [2S+2SH-1C+1C0] cycloaddition reaction can be carried out with diyne derivatives, showing these reactions give better yields than the corresponding intermolecular version (Scheme 80). 

Pyridine compounds 45 can also be produced by the NHC-Ni catalysed cycloaddition between nitriles 43 and diynes 44 (Scheme 5.13) [16]. The SIPr carbene was found to be the best ligand for the nickel complex in this reaction. The reaction required mild reaction conditions and low catalyst loadings, as in the case of cycloaddition of carbon dioxide. In addition to tethered aUcynes (i.e. diynes), pyridines were prepared from a 3-component coupling reaction with 43 and 3-hexyne 23 (Scheme 5.13). The reaction of diynes 44 and nitriles 43 was also catalysed by a combination of [Ni(COD)J, NHC salts and "BuLi, which generates the NHC-Ni catalyst in situ. The pyridines 45 were obtained with comparable... 

The reactions of Fischer carbene complexes with alkynes can under certain conditions lead to products that result from the incorporation of two alkynes, the carbene ligand and a carbon monoxide. In inter-molecular reactions, this is most commonly observed for acetylene itself or for sterically unhindered al-kynes. °2 As can be anticipated by the mechanism in Scheme 36, two-alkyne incorporated products of the type (258) are also favored for high alkyne concentration. Synthetically, the two-alkyne reactions are most useful in intramolecular reactions, two of which have been reported and are exemplified by the reactions in Scheme 43. The typical product from the reaction of a Fischer carbene complex with a diyne, such as (308), is a bicyclic phenol of the type (309). ° These products are apparently the result of the assembly of pieces indicated by (311). Under some conditions, dienones of the type (310) and (314) can be isolated, and it is thought they are the immediate precursors of the phenol products via an in situ reduction by a chromium(O) species. This reaction is completely regioselective with diyne (308) and the phenol (309) results from incorporation of the terminal alkyne of (308) before the disubstituted alkyne. Phenols of the type (309) have also been observed from the reaction of diynes with carbyne complexes. ... 

Key to method (A) exchange reaction with tin heterocycle (B) hydride addition to diyne (C) oxidation of saturated ketone (D) bromination-dehydrobromination by pyrolysis (E) reaction of RLi or ArLi with exocyclic M-Cl of preformed diene (F) ring expansion reaction from cyclopentadiene derivative (G) LiAlHi reduction of exocyclic M-Cl (H) carbene insertion into five-membered cyclo-pentadiene derivative. Doering-Hoffman method (I) 1,6-cycloaddition of GeCU. 

Another way in which dihydrobenzo[c]furans can be produced is through Ni(0)-catalyzed [2+2+2] cocyclotrimerization of arynes with diynes, as depicted in the following scheme <05CC2459>. Similar ruthenium- <05CC4438> and rhodium-catalyzed reactions <05CC3971>, as well as a carbene-Zn catalyzed reaction <050L3065> led to the formation of dihydrobenzo[c]furans. 

Louie et al. reported the nickel-catalyzed hetero-[2 + 2 + 2]-cycloaddition of CO2 with diynes. The reaction of the diynes 401 with CO2 under atmospheric pressures occurred in the presence of bis(1,5-cyclooctadiene) nickel and the 7V-heterocyclic carbene ligand (IPr, 403) to give the corresponding pyrones 402 in high yields (Scheme 128).189b... 

More recently Wulff and coworkers introduced a method based on the reaction of diynes 4 with bis(carbene) complexes 3 (Eq. 4.2) [6]. In contrast to the classical fragment condensation method, two phenol rings are formed during the key cyclization step. Since bonds to the substituted methylenes are not cleaved in the cyclization step, this method allows the preparation of chiral, optically active methylene-substituted calix[4]arenes, starting from the appropriate enantiopure precursors. 

In the original investigation, an attempt was made to observe the back reaction of the carbene with Nj to regenerate diazocyclopentadiene unlabeUed 15 was photolyzed in a matrix, but no Nj-substituted 15 was formed. It was therefore concluded that the elimination of Nj from 15 was irreversible. It was also observed that, on photolysis of the carbene 16 with an unfiltered medium-pressure Hg arc, a secondary photoproduct appeared with IR absorptions near 3315 cm", characteristic of a terminal alkyne. The secondary product was shown not be either ethyne or penta-l,4-diyne (19), but no further identification could be made at that time. 

The reaction of two equivalents of W(C=CC=CH)(CO)3Cp with Ru3(CO)io (NCMe)2 gives the RU3W cluster 149 (Scheme 30), which is also obtained from 135 and W(C=CC=CH)(CO)3Cp. The extended organic ligand is formed by coupling of two molecules of the diynyl complex with two of CO, to form a cyclopen-tadienone attached by a carbenic interaction to the cluster W atom, and featuring formylethynyl and C=CW(CO)3Cp substituents. " One of the elementary steps in the reaction mechanism may involve formal rearrangement of the diyne to a dicarbyne. 

As is clear from the introductory discussion, most, if not all, of the d-block transition metals are expected to participate in reactions that are related to those discussed here. In addition to the Co-based methodology mentioned earlier, some related reactions of Pd and are known. Also related are the cyclization reactions of metal-carbene complexes containing Cr, Mo, W and other transition metals with alkynes and alkenes and a recently reported Nb- or Ta-promoted diyne-alkyne cyclization reaction, which appears to be closely related to a number of previously developed alkyne cyclotrimerization reactions, such as those catalyzed by Co. Investigations of reactions involving other transition metals may prove to be important especially from the viewpoint of developing asymmetric and catalytic procedures. 

Alkynes react with various dichlorocarbene reagents to give 3,3-dichlorocyclopropenes 1, which can be hydrolyzed to cyclopropenones 2 in situ. The carbene reagents used are (A) chloroform, 50% sodium hydroxide, and triethylbenzylammonium chloride (TEBAC) (B) (bromo-dichloromethyl)phenylmercury (C) chloroform and potassium tert-butoxide and (D) chloroform and butyllithium. Although the yields of these reaction generally do not exceed 20%, a variety of cyclopropenones have been prepared by this method. The yields of biscyclo-propenones from diynes are very low. 

Scheme 3-6 Bis-cyclopentene formation via double Michael addition and carbene insertions in the reaction of nucleophiles with bis-iodonium diynes.

Many ruthenium-carbene five-membered ring compounds have recently been reported to show good activity for metathesis [51-71]. Many types of reactions, such as ring-closing metathesis, ring-opening metathesis, ctoss metathesis, enyne metathesis, and diyne metathesis, proceed with the help of these catalysts, as shown in Eqs. (8.15), (8.16), (8.17), (8.18), and (8.19) [58]. 

Compared to their carbene cousins, carbyne complexes, containing a metal-carbon triple bond, have seen very little development. One example is an interesting phenol synthesis by the reaction of a diyne 8.478 with a carbyne complex (Scheme 8.128). The reaction is remarkable for the low temperature at which it proceeds. " As in the Dotz reaction, the aromatic carbon atom bearing the hydroxyl substituent is derived from a carbon... 

Additionally, several nickel-catalyzed systems for pyridines synthesis have also been developed by Louie and coworkers. In 2005, they reported that with Ni(COD)2 as the catalyst and carbene as the ligand, the cyclization can be carried out at room temperature (Scheme 3.23a) [51]. Both intramolecular and intermolecular reactions were proceeded well and the cycloaddition of an asymmetrical diyne afforded a single pyridine regioisomer. This catalytic system was extended to cyanamides as well [52], In their systematic studies, they found the in situ formed dimeric [Ni(IPr)RCN]2 from the reaction of Ni(COD)2, IPr, and nitrile are catalytically competent in the formation of pyridines from the cycloaddition of diynes and nitriles. X-ray analysis revealed that these species display simultaneous f- and 17 -nitrile binding modes. Kinetic... 

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