Diynes heterocyclics

The preparation of condensed rhodacyclopentadienes via the diyne reaction, and examples of their use in heterocyclic synthesis have been described earlier (see Schemes 79 and 86 in Sections IV,B,5 and IV,C,2). An example showing the application of this approach to the synthesis of a condensed triazole is shown in Scheme 127.192... 

The diyne reaction has been used extensively by Muller et al. in heterocyclic synthesis (see for example Scheme 86 in Section IV,C,2) a process using a diyne substrate and leading to the formation of an azuleno[l,2-d]-dibenzo[b,/]silepin is shown in Scheme 172.243fl... 

The platinum-catalyzed diboration has been applied to some functionalized alkynes such as 1,3-diynes,44 1-borylalkynes,45 1,2-diborylethynes,46,47 and alkynylphosphonates.45 In particular, diboration of 1,2-diborylethyne gives tetraborylethene, which is a potential precursor for new boron heterocycles (Equation (2)).46,47... 

The Sonogashira reaction is of considerable value in heterocyclic synthesis. It has been conducted on the pyrazine ring of quinoxaline and the resulting alkynyl- and dialkynyl-quinoxalines were subsequently utilized to synthesize condensed quinoxalines [52-55], Ames et al. prepared unsymmetrical diynes from 2,3-dichloroquinoxalines. Thus, condensation of 2-chloroquinoxaline (93) with an excess of phenylacetylene furnished 2-phenylethynylquinoxaline (94). Displacement of the chloride with the amine also occurred when the condensation was carried out in the presence of diethylamine. Treatment of 94 with a large excess of aqueous dimethylamine led to ketone 95 that exists predominantly in the intramolecularly hydrogen-bonded enol form 96. 

Rhodium-catalyzed three-component domino coupling of 1,6-diyne 41, hydrosilane, and Cgo proceeds to give fullerene adduct 42 in good yield (Eq. 10) [29]. In this case, dienophile Cgo does not interfere with the silylcarbocyclization process and traps the 1,2-bis-exo-methylidenecyclopentane intermediates to furnish the corresponding Cgo-linked carbo- or heterocycle 42. 

An jco-OT o-cyclisation of a,o -diynes promoted by bis(pyridyl)iodonium(i) tetrafluoroborate (IPy2BF4) has been described for the first time and is an excellent route for accessing a variety of sulfur-containing heterocycles when employing alkynyl sulfides (Scheme 49) <1998AGE3136>. 

Likewise, no products of the anti-Michael addition were found in the reaction above. Compound 27 was obtained in 28% yield in the case of 1,5-diphenylpenta-l, 4-diyn-3-one (82JOC1968) when bis(ferf-butyldimeth-ylsilyl) telluride was used as the source of telluride anion. Heterocycle 22 (R1 = R2 = Ph) is also formed (in 19% yield). 

The attempts to apply both of the above-described reactions for the preparation of the parent heterocycle 22 (R1 = R2 = H) with the use of penta-l,4-diyn-3-one were only partially successful. The yields of 22 (R1 = R2 = H) were lower than 5%, the main products being unidentified oligomers (92MI3). The first synthesis of 22 (R1 = R2 = H) of preparative significance was when l,5-bis(trimethylsilyl)penta-l,4-diyn-3-one was the... 

Nickel-mediated intramolecular cyclizations of enynes, dienynes, bis-dienes and diynes leading to heterocycles 92SL539. 

Pyrans constitute another class of oxygen-containing heterocycles that have been prepared from Ni-catalyzed cycloaddition reactions. The coupling of diynes and aldehydes could be mediated by the combination of a Ni(0)... 

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. 

For larger rings, heteracycloalkane or heteraannulene are used for example, 10 will be called 1,6-ditelluracyclodo-decane, while 11 will be 2,ll-diselena[3.3]metacyclophane. The last ring mentioned here is exemplified by 12, which is a 15-member heterocycle containing four atoms of selenium it is called l,4,8,ll-tetraselena-cyclopentadeca-2,9-diyne. 

Buta-l,3-diyne, reaction with ethylenediamine, 56, 9 Butane-2,3-dione, perlluoro-, heterocycles from, 59, 17... 

Rh(l)-catalyzed [2-I-2-I-2] cyclotrimerization of 1,6-diynes (e.g., 1391 and 1394) with monoynes (e.g., 1392) in combination with stereospecific Ag(i)-catalyzed aldimine (metallo)azomethine ylide — cycloaddition cascades affords rapid access to complex heterocyclic benzene derivatives 1393 and 1395 in one-pot processes with the generation of five new bonds, four stereocenters and three rings (Schemes 266 and 267) <2000T8967>. 

A wide variety of main group heteroatom-containing ring systems are formed by the reaction of appropriate reagents with metallacycles derived from cycloaddition of Cp2Zr with alkynes, diynes, dienes, enynes or alkynenitriles. This is an exceptionally general process of considerable potential, especially for the synthesis of less-common types of heterocycles (Schemes IS and 16). ... 

Polyynes have served as starting materials for the synthesis of a wide variety of heterocyclic ring systems. The reactions used involve addition to triple bonds, and any of the common mechanistic pathways may be followed, i.e. nucleophilic, electrophilic or free radical attack as well as concerted cycloadditions. Although the evidence does not permit unequivocal classification of many of the reactions into one of these categories, the ones considered here are those which most likely involve nucleophilic attack at some stage. In a formal sense the reactions amount to successive additions of a divalent nucleophile to two triple bonds the first involves intermolecular and the second intramolecular attack, as illustrated in equation (19) for the addition of HoS to a diyne. 

One of the reactions that has been particularly useful in the generation of heterocyclic derivatives of Groups III and V is the exchange reaction with a tin heterocycle (normally derived by the direct reaction of a tin dihydride with a 1,3 diyne). The successful generation of Group V and III analogs of benzene relies on this synthetic route 11-13, 15) ... 

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