Diynes bicyclization

The THF adduct 70 (mp 147 °C) and pyridine adduct 71 (mp 178°C) of bis-l-boraadamantane with one CH2 bridge were synthesized by hydroboration-cyclization of the bis-bicycle 72, available from hepta-l,6-diyne (Scheme 28) . 

The Ti-promoted intramolecular alkyne-alkyne coupling of tethered diynes was extensively developed earlier with TiCp2 derivatives as reagents65 66 (Equation (1) of Scheme 22). Bicyclic titanacyclopentadienes fused to... 

Scheme 37 Zr-promoted bicyclization of enynes, dienes, and diynes. Some natural products synthesized by these reactions.

Scheme 53 Bicyclization of diynes with group 6 metal-carbyne complexes.

Although mechanistic details are unclear, a very interesting Mn-induced bicyclization of diynes shown in Scheme 62 has been reported.270 Unfortunately, this reaction gives mixtures of three isomeric products. 

Itoh and co-workers reported the ruthenium(n)-catalyzed [2 + 2 + 2]-cycloaddition of 1,6-diynes with isocyanates to afford the corresponding bicyclic pyridones 163 (Scheme 72).356 357 For previously reported ruthenium-catalyzed [2 + 2 + 2]-cycloaddition of 1,6-diynes see Refs 358 and 358a, and for theoretical calculations of the cyclocotrimer-ization of alkynes with isocyanates, isothiocyanates, and carbon disulfide see Refs 359 and 359a. 

The reaction of nBu2ZrCp2 with 2 equivalents of PhC CPh provides the novel bicyclic gem-dizirconium complex 140 [236] (Scheme 7.42). Protonolysis of complex 140 with 3 n HC1 gives bibenzyl in 88% yield, while its deuterolysis with D20 provides tetradeuterio-bibenzyl 141 with 92 % deuterium incorporation. The dual path nature (142 versus 140) of the reaction of Cp2Zr with alkynes is an important factor in designing Zr-promoted cyclizations of alkynes, enynes, and diynes. 

The above bicyclization could be extended to functionalized diynes, permitting the preparation of lactams or lactones having a fused exocyclic conjugated diene, a representative example of which is shown in Eq. 9.53 [98],... 

Low-temperature photochemical cyclization of alkynes bearing a bulky substituent, mediated by CpCo(CO)2, proceeds with CO insertion to give cyclopentadienone complexes. Higher reaction temperatures lead to cyclotrimerization. The intramolecular variant of this reaction gives the bicyclic cyclopentadienones 139 and 139 (equation 19)142. Cyclization of unsymmetrically substituted diynes with the chiral R CpCo(CO)2 (R = 8-phenylmenthyl) leads to the formation of a mixture of diastereomers modest diastere-oselectivity was found. 

Diynes have already been used for building polycylic compounds in the presence of CO2 and a stoichiometric amount of Ni(0) bicyclic pyrones were obtained [117]. With the electrocarboxylation method, linear or cyclic mono-carboxylic acids were obtained as main products from non-conjugated diynes depending on the ligand associated to Ni [118, 119]. Thus ring-fomation occurred with the Ni-bipyridine complex at normal pressure of CO2 on the other hand, in the presence of PMDTA as ligand and with a 5 atmosphere pressure of CO2, linear adducts were mainly formed as illustrated in Eq. (16) ... 

Vaska s complex ([IrCl(CO)(PPh3)2]) also catalyzed the carbonylative coupling of diynes, which provided bicyclic cyclopentadienones (Scheme 11.23) [35]. Due to the instability of the products, the substrates are limited to symmetrical diynes with aromatic groups on their termini nonetheless, this reaction still serves as the catalytic and practical procedure for the synthesis of cyclopentadienones, which are anti-aromatic with a 47t system and serve as active synthetic intermediates. 

Iridium-phosphine complexes were found to be efficient carbonylative alkyne-alkene coupling catalysts [62]. Although frequently applied in other transformations, the dimeric complex [ Ir( x-Cl)(cod) 2] appeared to be a very active catalyst in the coupling of silylated diynes with CO [63], giving bicyclic products with a carbonyl moiety (Scheme 14.12). 

Dipropargyl ethers can be cyclized to isobenzofurane derivatives both in palladium or nickel catalysed transformations. In the former case dipent-2-ynyl ether was coupled with allyl tosylate to give the corresponding bicycle, albeit in poor yield.115 The same ring system was obtained in good yield in the nickel catalysed reductive cyclization of the diyne and the allene shown in 3.91... 

The Rh4(CO)i2-catalyzed reactions of 1,6-diynes at 95 °C and 20 atm of CO in benzene or acetonitrile are less selective than those catalyzed by Rh2Co2(CO)i2 or Rh(acac)(CO)2, and a different type of silylcarbobicyclization product, azabicyclo[3.3.0]octadienone (351), is formed in addition to 349-type product (352) when benzyldipropargylamines (350) are used (equation 142)339. The formation of a small amount (5%) of the bicyclic pyrrole of 351-type with 7V-tosyl group is also observed besides 348-type (18%) and 349-type (51%) products in the reaction of IV-tosyldipropargylamine339. 

Novel carbonylative carbocyclizations of 1,6-diynes promoted by Ru3(CO)i2/P(hex-c)3 in the presence of HSiMc2Bu-Z give bicyclic o-catechol derivatives by incorporating two carbon monoxide molecules as the 1,2-dioxyethenyl moiety (equations 148 and 149)346. This reaction is tolerant of functional groups such as ester, ketone, ether and amide. The disilylated product 366 is formed through dehydrogenative silylation of the initially formed mono-silyl product 365 under the reaction conditions. 

Intramolecular trapping of the transient carbene postulated above has also been achieved yielding polyunsaturated bicycles (47) from the diene-diyne precursor (46).42 The intramolecular cyclopropanation is preceded by a [l,3]-metallotropic shift. 

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