Cobalt diyne reactions

An example illustrating the synthesis of condensed oxepins by the cobalt-catalyzed reaction of bistrimethylsilylacetylene with a hexa-l,5-diyne derivative is shown in Scheme 175.234 This type of process has been discussed earlier in the context of pyran synthesis (see Scheme 158 in Section V,B,2). 

The regiochemical product distribution of the co-cyclization of two or three different alkynes occurs statistically. In some cases carefully controlled reaction conditions allow isolation of a main product from mixed cyclotrimerizations. For example, l,2,3,4-tetraphenyl-5,6-diethylbenzene can be obtained from cobalt-catalyzed reaction of tolane and 3-hexyne in good yield [62]. The first example of an intermolecular, regiospecific cross-benzannulation reaction catalyzed by Pd(PPh3)4 was reported by Yamamoto [63]. The reaction of 2-alky 1-but-l-ene-3-yne with disubstituted diynes leads exclusively in high yields to... 

Substituted benzocyclobutenes, indans, and tetralins can be synthesized in good yield by the related co-oligomerization of a,cobalt-catalysed reaction of a,a>-diynes is their reac-... 

The total synthesis of ( )-estrone [( )-1 ] by Vollhardt et al. is a novel extension of transition metal mediated alkyne cyclotrimeriza-tion technology. This remarkable total synthesis is achieved in only five steps from 2-methylcyclopentenone (19) in an overall yield of 22%. The most striking maneuver in this synthesis is, of course, the construction of tetracycle 13 from the comparatively simple diyne 16 by combining cobalt-mediated and ort/io-quinodimethane cycloaddition reactions. This achievement bodes well for future applications of this chemistry to the total synthesis of other natural products. 

A hydrosilylation/cyclization process forming a vinylsilane product need not begin with a diyne, and other unsaturation has been examined in a similar reaction. Alkynyl olefins and dienes have been employed,97 and since unlike diynes, enyne substrates generally produce a chiral center, these substrates have recently proved amenable to asymmetric synthesis (Scheme 27). The BINAP-based catalyst employed in the diyne work did not function in enyne systems, but the close relative 6,6 -dimethylbiphenyl-2,2 -diyl-bis(diphenylphosphine) (BIPHEMP) afforded modest yields of enantio-enriched methylene cyclopentane products.104 Other reported catalysts for silylative cyclization include cationic palladium complexes.105 10511 A report has also appeared employing cobalt-rhodium nanoparticles for a similar reaction to produce racemic product.46... 

Cobalt carbonyl adducts of buta-l,3-diyne are best obtained via indirect methods. Very early work showed that the reaction between Hg Co(CO)4 2... 

Cobalt carbonyl complexes react with 1,3-diynes to give a variety of complexes in which two molecules of diyne have coupled to form y-cyclobutadiene ligands slightly different conditions result in formation of cluster complexes (see Section VILE.2). In the mixture of complexes obtained from the reaction... 

Formal silylcarbonylation and silylformylation reactions are mainly catalyzed by cobalt and rhodium complexes (clusters) yet, Chatani et al. [158] have found a new type of carbonylation of diynes with trialkylsilanes leading to catechols (Eq. 100). 

In contrast to the thermal reactions of 1-alkynylboronic esters, the cycloaddition smoothly takes place under very mild conditions in the presence of metal catalysts (Scheme 28). A cobalt(i) complex catalyzed the [4+2]-cycloaddition of alkynyl boronates with 1,3-dienes to give cycloalkenyl boronates 266431 and with ct,cu-diynes giving arylboronates... 

In previous works this group had observed a competition between the PKR and a [2 + 2 + 2] cyclization in the second reaction step of three triple bonds. Thus, when reacting linear triynes 174 under catalytic, high CO pressure, cobalt mediated PKR conditions, they obtained mixtures of products 175 coming from two [2 + 2 + 1] cycloadditions, and 176 from a [2 + 2 + 1]/ [2 + 2 + 2] tandem reaction. When the triple bonds were ether linked, the latter was the favored reaction, while with substrates lacking oxygen atoms, the iterative PKRs was the major pathway (Scheme 51) [166]. When the reaction was performed intramolecularly between a diyne and an alkyne, the only reaction products were the result of a [2 + 2 + 1 ]/[2 + 2 + 2] tandem cycloaddition [167,168]. 

It is also worthy of note that the construction of tetracyclic compounds 44 by cobalt-catalyzed tandem Pauson-Khand/[2 + 2 + 2] cycloaddition reactions of 1,6-diynes 43 was also reported by Chung et al. [45,46]. It was experimentally shown that the [2 + 2 + 2] cycloaddition reaction occurs after the [2 + 2 + 1] cycloaddition between CO and the substrate (Scheme 22). 

The cobalt(I)-mediated [2 + 2 + 2] cycloaddition of 1,5-diynes with mono-alkynes provides access to benzocyclobutene derivatives (Scheme 24). Thermal rearrangement of benzocyclobutenes into o-quinodimethane and subsequent Diels-Alder reaction with an alkene moiety allow the formation of a tricyclic compound. 

Indole N-substituted diyne tetracobalt complexes 1467 undergo a Lewis acid-mediated dimerization-cyclization reaction through the indole 3-position to afford indolophanetetrayne cobalt complexes 1468 (Scheme 280) <20030L1003>. 

Tetrahedrane (11) is the ruthenium analog of the much-studied tricobaltnonacarbonyl clusters Co3(CO)9CR see Cobalt Organometallic Chemistty). The substitution chemistry of (11) has been studied. A starting material is prepared from (11) by reaction with BX3 (equation 2), which gives the chloro and bromo compounds (12). In addition, (11) can also be treated directly with compounds such as diynes to yield interesting substitution products. For example, when (11) is refluxed in THF with diphenylbutadiyne, cis- and trans-alkene isomers of two alkyne insertion regioisomers are formed (equation 3). The product seems to arise from dehydrogenation of one end of the diyne to yield cis and trans enynes and an imsaturated monohydride cluster intermediate, which then reacts with the enynes to yield the allylic derivative products... 

The reaction of dienes, diynes, or en-ynes with transition metals " (usually cobalt) " forms organometalhc coordination complexes. In the presence of carbon monoxide, the metal complexes derived primarily from enynes (alkene-alkynes) form cyclopentenone derivatives in what is known as the Pauson-Khand... 

---