Cycloaddition with diynes

Ethoxy(trimethylsilyl)acetylene reacted by a [2 + 2 + 2] cycloaddition with diyne 11 in the presence of 10 mol% Rh(cod)2-BF4 and 10 mol% rac-BlNAP in dichloromethane (0.021 M) at ambient temperature to give aryl ether derivative 12 in 50% yield, thus providing a valuable synthetic route to highly substituted benzene derivatives (eq 9). ... 

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). 

Ruthenium(ll)-catalyzed cycloadditions of diynes with bicycloalkenes illustrate the synthetic importance of ruthena-cyclopentatrienes as biscarbenoid intermediates.380 Reaction of 1,6-diyne 448 and biscyclic alkene 449 with ruthenium catalyst afforded a mixture of biscyclopropanation product 450 and cyclotrimerization product 451 (Scheme 113). 

Ikeda and coworkers351 performed [2 + 2 + 2] cycloadditions of diynes with a,ji-enones using NiCl2/Zn (1 10) as the catalytic couple. In these reactions, nickel dichloride... 

Benzo[l,2-A4,5- ]dithiophene 22 undergoes photochemical [2n+2n] cycloaddition with electron-deficient buta-diynes on irradiation at 300 nm to produce photoadducts in low yields. The reaction with dimethyl acetylenedicar-boxylate proceeds directly to produce the secondary photoadduct 56 (Equation 6) <2003JOC8258>. 

Nitrogen-based heterocycles can also be prepared through Ni/NHC-catalyzed cyclo addition reactions. For example, Ni/SIPr catalyzed the cycloaddition of diynes with isocyanates under the mildest conditions to date [26]. In particular, excellent yields of pyridones are obtained from diynes and isocyanates at room temperature using only 3 mol % catalyst. As shown in Eq. 8, a variety of diynes were subjected to these optimized conditions. Both aryl and alkyl isocyanates were readily converted to the respective 2-pyridone. Sterically hindered substrates appeared to have very little effect on the reaction, as excellent yields of product were obtained with bulky isocyanates and bulky diynes. 

In contrast to isocyanates, isothiocyanates have hardly been examined as cycloaddition components, because the strong coordination of organosulfur compounds frequently deactivates a catalytic species [21]. Some organoruthe-nium complexes, however, recently proved to be efficient catalysts for the formation of carbon-sulfur bonds [21]. The catalytic cycloaddition of diynes with isothiocyanates was also successfully achieved using Cp RuCl(cod) as a precatalyst [22]. Importantly, the cycloaddition took place at the C=S double bonds of the isothiocyanates to afford thiopyranimines 26 (Eq. 13). This reaction requires 10 mol % of the precatalyst as well as the diynes possessing a quarternary carbon center at the 4-position. When excess amounts of carbon disulfide were also employed in place of the isothiocyanates, a bicyclic dithiopyrone 26 [X is C(C02Me)2, Z is S] was obtained in 50% yield. 

Fused 2//-pyran-2-ones are formed in excellent yields and under mild conditions through a Ni-catalysed [2+2+2] cycloaddition of diynes and C02 <02JA15188>. Oxidative demetalation of 0i3-allyl)Mo complexes of pyran with pyridinium dichromate (PDC) introduces a carbonyl function at the allylic terminus offering access to dihydropyranones of high enantiopurity <02JOC5773>. 

Scheme 54 Cycloaddition of diynes with dienes in the synthesis of triquinanes. Tandem [2 + 2 + l]/[4 + 2] cycloadditions...

A novel cycloaddition of diynes with aldehydes is catalyzed by the same metal system, giving rise to bicyclic a-pyrans after 1,5-hydrogen shifts. Yields of these sensitive compounds are remaritably high (equation 52). ... 

Scheme 39. Catalytic [2 + 2 + 2]-Cycloaddition of Diynes with (a) Alkynes, (b) Allenes, and (c) Alkenes...

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... 

The 1,3,5/l -diazaphosphinines react with alkynes in a cascade of (4 + 2)-cycloaddition and cycloreversion reactions, giving the substituted 2 -phosphinines (190) (Scheme 37) <91AG(E)106,92TH625-01 >. With diynes the cycloadditions yield oligomeric phosphinines, and finally polymers with P-phosphinine units <96TH 625-01 >. 

Isoindolines and isoquinolines a,co-Diynes in which the connecting chains contain a nitrogen atom undergo [2+2+2]-cycloaddition with ketene equivalents derived from the carbene complexes. After the formation of a benzene ring, the products are isoindoline or isoquinoline derivatives. 

Finally, a double [2+2] cycloaddition with p-dibromobenzene and 1,1-dimethoxy-ethylene gave, after acid hydrolysis, a 20% yield of the novel bis-benzocyclobutenone 483. Thus p-dibromobenzene acts as a synthetic equivalent for diyne 434, and cycloaddition to the presumed intermediate aryne 484 is regioselective. 

VolLhardt and coworkers further investigated the scope of these [2+2+2] reactions [99]. They explored the intermolecular reactions between simple A-substituted indoles and diynes. With these substrates 263, the CpCo(CO)2 catalyst used above led only to diyne trimers and ohgomers, but no desired cycloaddition products. However, the use of CpCo(C2H4)2 led to the formation of the desired cycloaddition cobalt complexes in moderate yields. It is interesting to note the difference in reactivity observed for 263 when treated with unsubstituted and trimethylsUyl-substituted diynes (Scheme 70). While the use of unsubstituted 1,6-heptadiyne (264) failed to produce the desired cycloaddition product, the cycloaddition with 1-trimethylsilyl-1,6-heptadiyne (265) resulted in the formation of a single regioisomeric product 266 in 36% yield. In contrast, the reaction of 1,7-octadiyne (267) with 263 produced... 

Furan also undergoes a primary [4+2] cycloaddition with 3, but this is followed by a [2+1] addition of 2 to the newly formed double bond to furnish the isolated tricyclic compound 5. Thiophene behaves differently its reaction with 3 furnishes the disilathiirane 6 as a formal sulfur-abstraction product [3]. This strongly divergent behavior of five-membered ring systems prompted us to investigate the photolyses of 1 also in the presence of a selenophene, a tellurophene, and a pyrrole. We report here on the photolysis of 1 in the presence of these cyclic dienes as well as similar reactions with acyclic diynes. 

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