Diynes from alkynes

The 62-e diyne complexes 115 and 116 are effective scaffolds for the trimeriza-tion of the diynes and codimerization of diyne and alkynes, resulting in extended carbon chains coordinated to the cluster. Thus, reactions with R C=CC=CR (R = Ph, Me) afforded Ru4(M4-PPh) /i4-RCC(CsCR )CPhC-p -CCPhCRC (C=CR ) (CO)s (118 R = Ph, Me). The former was also found as a minor product from Ru4(/i4-PPh)(CO)i3 and PhC=CC=CPh. " These are 64-e clusters containing a /44-PPh ligand capping an RU4 face, together with a C12 ligand formed from... 

Diynes. A synthesis of the skipped diynes from 1-alkynes and propargyhc mesylates involves prior conversion of the former compounds into aluminum derivatives. 

Triazole Derivatives. Triazole derivatives are known to possess tumor necrosis factor-a (TNF-a) production inhibitor activity. The synthesis of triazole derivatives can be achieved from alkynes or diynes by a tandem cascade reaction involving 1,3-dipolar cycloaddition, anionic cyclization and sigmatropic rearrangement on reaction with sodium azide. Some of the benzoyl triazole derivatives were considered to be potent local anaesthetics and are comparable with Lidocaine. The triazoles can also be prepared from benzoyl acetylenes,triazoloquina-zoline derivatives, 2-trifluoromethyl chromones, aliphatic alkynes, 2-nitroazobenzenes, ring opening of [ 1,2,4]triazolo [5,1-c] [2,4]benzothiazepin-10 (5//)-one, alkenyl esters and dendrimers. A number of these reactions are outlined in eqs 44 8. 

Pyridones or Pyrimidine-diones from Diynes or Alkynes and Isocyanates... 

Synthesis of Highly Substituted Indenocorannulenes from Diynes and Alkynes... 

Dimerization with Insertion of One Molecule of CO. A number of tricarbonyliron complexes of substituted cyclopen-tadienones have been prepared from alkynes. The reaction was first described by Jones et al. " for FefCOJj and Ph-C=CH in the presence of Ni(CO)4. A number of other alkynes (PhC2Me, PhC2SiMc3, Mc3SiC2R, BrCgH4C2H, CF3C2CF3, PhC2Ph and a,(i)-diynes) give cyclopentadienone complexes (eq 30). ... 

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. 

While diene metathesis or diyne metathesis are driven by the loss of a (volatile) alkene or alkyne by-product, enyne metathesis (Fig. 2) cannot benefit from this contributing feature to the AS term of the reaction, since the event is entirely atom economic. Instead, the reaction is driven by the formation of conjugated dienes, which ensures that once these dienes have been formed, the process is no longer a reversible one. Enyne metathesis can also be considered as an alkylidene migration reaction, because the alkylidene unit migrates from the alkene part to one of the alkyne carbons. The mechanism of enyne metathesis is not well described, as two possible complexation sites (alkene or alkyne) exist for the ruthenium carbene, leading to different reaction pathways, and the situation is further complicated when the reaction is conducted under an atmosphere of ethylene. Despite its enormous potential to form mul-... 

Diyne 66, which possesses a three carbon linkage between the alkynes, also reacts with aldehyde 67 in presence of [Ni(COD)J/SIPr catalytic system (Scheme 5.19). However, the connectivity of the dienone 69 obtained from this diyne was different from those obtained from diyne 60. In the former case, adduct 69 was obtained from a )5-hydride elimination of the nickelacycle 68 instead of a reductive elimination. 

Amatore et al. developed an aqueous cross-coupling reaction of terminal alkynes with 1-iodoalkynes using a water-soluble Pd(0) catalyst prepared in situ from Pd(OAc)2 and sulfonated triphenylphosphine P(C6H4 — m-SCENa (TPPTS) without Cu(I) promoter, giving diynes with moderate yields (43-65%)(Eq. 4.22) 42... 

An interesting series of ring-closing alkyne metathesis reactions (RCAM) has recently been reported by Fiirstner and coworkers (Scheme 6.72) [152], Treatment of biaryl-derived diynes with 10 mol% of a catalyst prepared in situ from molybdenum hexacarbonyl and 4-(trifluoromethyl)phenol at 150 °C for 5 min led to a ca. 70% iso-... 

As is clear from the mechanisms, these reactions cannot occur with methylmetals. Their extensions beyond ethylmetallation are possible, but are prone to various side reactions [201,202], In contrast to the widely observable Zr-catalyzed carboalumination of al-kynes discussed earlier, the alkyne version of the Zr-catalyzed ethylmagnesation has not been widely observable, the only successful examples being those of conjugated diynes [203], In this context, further investigation of the Zr-catalyzed carbozincation of alkynes reported as early as 1983 [204,205] appears to be very desirable. 

When the terminal alkynes 96 are treated with the trimethylsilylalkyne 97 in the presence of HfCl4 as a Lewis acid, the silylated vinylallenes 98 are produced in acceptable yields. In an intramolecular variant of this process, 100 was obtained from the diyne 99 [32]. Vinylallenes, incorporated into a cyclic framework and hence of restricted conformational mobility, are of interest for photochemical studies [33] and are among the photoproducts in ring-enlargement reactions of polycyclic allenes [34]. 

Hashmi et al. investigated a number of different transition metals for their ability to catalyze reactions of terminal allenyl ketones of type 96. Whereas with Cu(I) [57, 58] the cycloisomerization known from Rh(I) and Ag(I) was observed (in fact the first observation that copper is also active for cycloisomerizations of allenes), with different sources of Pd(II) the dimer 97 was observed (Scheme 15.25). Under optimized conditions, 97 was the major product. Numerous substituents are tolerated, among them even groups that are known to react also in palladium-catalyzed reactions. Examples of these groups are aryl halides (including iodides ), terminal alkynes, 1,6-diynes, 1,6-enynes and other allenes such as allenylcarbinols. This che-moselectivity might be explained by the mild reaction conditions. 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

The Pd-catalyzed electro-cleavage of the C—O bond of allyl aryl ether proceeds smoothly in a DMF-Bu4NBp4-(Mg)-(Stainless Steel) system, giving depro-tected products in 73 99% yield [437]. The sp-sp intermolecular coupling reaction with the Pd water-soluble catalyst prepared in situ from Pd(II) acetate and sul-fonated triphenylphosphine in an MeCN-H2O system yields diynes in 45 65% yields [438]. Similarly, the sp -sp coupling of 2-iodophenols or 2-iodoanilines and terminal alkynes followed by intramolecular cyclization gives indol and furan... 

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