1.2.3- Trienes acetylene derivatives

The synthesis of highly strained linear and angular dicyclopropabenzenes has been attempted without success, since the precursors required for the cleavage could not be synthesized. Thus, iV77-l,6 7,12-diinethano[14]annulene 3 underwent addition to acetylenedicarbonitrile in the wrong sense and did not lead to the required norcaradiene. Cycloaddition of dimethyl acetylenedicarboxlate to cyclopropa-1,6-methano[10]annulene would provide a precursor 4 for the linear dicyclopropabenzene however, the desired cycloadduct was not obtained. In this context, cyclopropa-1,6-methano[10]annulene gave no cycloadduct with 4-phenyl-4//-1,2,4-triazol-3,5-dione. On the other hand, the addition product 5 of 1.6-dimethylenecyclohepta-triene with 1 -bromo-2-chlorocyclopropene reacted with the acetylene derivative, but the twofold dehydrochlorination did not lead to the required norcaradiene. ... 

Dienes from 1,2,3-trienes via reductive carboxylation Synthesis of acetylene derivatives from 1,2,3-trienes Reductive alkylation... 

Lithium tetrahydridoaluminate/methanoI trans-Ethylene from acetylene derivs. Selective hydrogenation 1,2,4-Trienes... 

If the alkenes and acetylenes that are subjected to the reaction mediated by 1 have a leaving group at an appropriate position, as already described in Eq. 9.16, the resulting titanacycles undergo an elimination (path A) as shown in Eq. 9.58 [36], As the resulting vinyltitaniums can be trapped by electrophiles such as aldehydes, this reaction can be viewed as an alternative to stoichiometric metallo-ene reactions via allylic lithium, magnesium, or zinc complexes (path B). Preparations of optically active N-heterocycles [103], which enabled the synthesis of (—)-a-kainic acid (Eq. 9.59) [104,105], of cross-conjugated trienes useful for the diene-transmissive Diels—Alder reaction [106], and of exocyclic bis(allene)s and cyclobutene derivatives [107] have all been reported based on this method. 

When unstable 9,10-dihydrofulvalene 804) is allowed to react with dimethyl acetylene-dicarboxylate, a separable mixture of the adducts 805 and 806 is produced The diacid derived from 805 can be readily transformed into diketone 807 and subsequently into triene dione 808 (Scheme XCVIII) Once the intramolecular photocycliza-... 

Ortho photocycloaddition was first reported in a U.S. patent [1] dated September 3, 1957. Irradiation of benzonitrile in the presence of various alkenes resulted in the formation of derivatives of l-cyanobicyclo[4.2.0]octa-2,4-diene. The first ortho photocycloaddition to benzene was reported in 1959 by Angus and Bryce-Smith [2], who discovered that benzene and maleic anhydride react to form a stable adduct at 60°C under the influence of ultraviolet radiation. This 1 2 adduct was formed from one molecule of benzene and two molecules of maleic anhydride. Two years later, Bryce-Smith and Lodge [3] found that acetylenes could also be photoadded to benzene. The isolated products were cyclooctatetraenes, formed by ring opening of the primarily formed bicyclo[4.2.0]octa-2,4,7-trienes. Since those early years, hundreds of examples of ortho photocycloadditions of alkenes to the benzene ring and many mechanistic investigations have been reported and they will be discussed in this chapter. 

The primary ortho adducts formed from benzene derivatives and acetylenes are derivatives of bicyclo[4.2.0]octa-2,4,7-triene. These products usually are not isolated but isomerize during the irradiation to cyclooctatetraenes [58,59,68,72], From combinations of hexafluorobenzene and pentafluoroalkoxybenzenes with various disubstituted acetylenes, however, the isolation of relative stable primary ortho adducts has been reported [65-67], In Scheme 46, the products of the photochemical reaction of hexafluorobenzene with but-2-yne are shown [67],... 

Tandem hydrostaimation/cross-coupling is a powerful tool for C-C bond formation starting from acetylenes. A vinylstaimane derived from butynol by AIBN-mediated hydrostannation underwent the cross-couphng with a dienyl iodide under the influence of palladium catalyst to furnish racemic phthoxazohn A (Scheme 12.106) [208]. In this total synthesis a Z,Z, -triene unit was efficiently assembled by exploiting this hydrostannation/cross-coupling procedure. 

Apart from the technical route described to p-apo-8 -carotenal, readily available vitamin A alcohol (Cjo) has served as an intermediate in the form of the phosphonium salt by reaction with the monodiethyl acetal of a Cio dial (ref. 54). The required Cjo monodiethylacetal was obtained (ref.5, p409) by the reaction of the mono aldehyde-protected derivative, the enol ether of methylmalonaldehyde, (C4) with the acetylenic Grignard reagent from trans 3-methyl-2-penten-4-yn-l-ol (C ) followed by acidic dehydration and partial reduction with Lindlar catalyst to give firstly 8-hydroxy-2,6-dimethylocta-2, 4,6-triene-l-al (Cio). Protection of the hydroxyl group by acetylation in pyridine solution with acetyl chloride and formation of the diethyl acetal with ethyl orthoformate followed by hydrolysis of the acetyl group and oxidation afforded the final CIO aldehyde component (D)shown in Scheme 15a. 

The metathesis copolymerization of the cyclobutene derivative, 7,8-bis(trifluoro-methyl)tricyclo[4.2.2.0 ]deca-3,7,9-triene (MO (7 in Ch. 13), with norbomene or cyclopentene (M2) gives copolymers that are readily converted into acetylene copolymers by elimination of l,2-bis(trifluoro)benzene from the Mi units, but the compositional sequence distribution in these copolymers is difficult to establish (Ramakrishnan 1989b). 

A general procedure has been published for the synthesis of retinoids, including vitamin A, by direct condensation of the side-chain, as ethyl 3,7-dimethylnona-2,4,6-trien-8-ynoate (80) to the appropriate cyclic ketone, e.g. 2,2,6-trimethyl-cyclohexanone (81). The acetylenic intermediate (82) is readily converted into vitamin A and derivatives. The side-chain reagent (80) is prepared in high yield by Emmons reaction between the acetylenic aldehyde (83) and the phospho-senecioate (84). In another synthesis of trans- tamm A, jS-ionylideneacetal-... 

In a similar fashion, heptafulvene, i.e., 7-methylenecyclohepta-l,3,5-triene, adds to the acetylenic ester to give a dihydroazulene derivative (Scheme 4.30). 

Urushi is a Japanese traditional natural paint. The main component of urishi is urishiol (Scheme 12.21), whose structure is a catechol derivative with unsaturated hydrocarbon chains consisting of a mixture of monoenes, dienes and trienes at the meta or para position of catechol. Kobayashi and co-workers [204] have carried out laccase-catalysed crosslinking reactions with urishiolanalogues to prepare urishi. The HRP-catalysed polymerisation of w-ethynylphenol (HO-Cf H4-C=CH), containing more than one polymerisable group, showed that the phenol moiety was chemoselectively polymerised when an acetylene or methacryl group were present [205]. 

Trimerization of alkynes to form aromatic compounds has been achieved first by Reppe and Schweckendiek using nickelcarbonyl complexes as catalysts. The applicability of carbonyliron complexes for this purpose was reported as early as 1960. Unsymmetric acetylenes give exclusively the arenes with symmetric substitution pattern under these conditions (Scheme 4-309). Alternatively, (Ti -arene)iron complexes such as bis(ethene)(toluene)iron can be used for the cyclotrimerization of unsymmetric alkynes. A variety of symmetrically substituted benzene derivatives has been obtained. Another very active precatalyst for this reaction is (Ti -cyclohepta-l,3,5-triene)(T -cycloocta-l, 5-diene)iron(0). ... 

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