Ring acetylene derivs

Diol Components. Ethylene glycol (ethane 1,2-diol) is made from ethylene by direct air oxidation to ethylene oxide and ring opening with water to give 1,2-diol (40) (see Glycols). Butane-1,4-diol is stiU made by the Reppe process acetylene reacts with formaldehyde in the presence of catalyst to give 2-butyne-l,4-diol which is hydrogenated to butanediol (see Acetylene-DERIVED chemicals). The ethynylation step depends on a special cuprous... 

Kotlyarevsky et al. (69TZV927) showed that ketones that are not substituted on the nitrogen of the ring lead to certain complications. Thus, under normal conditions (60CB593), 4-acetyl-3,5-dimethylpyrazole (6) gave a product containing significant quantities of the respective acetylene derivative 11 and an unexpected chloroacetylene 10. 

For this reason, the heterocyclization of acetylenic derivatives of pyrazolecar-boxylic acids with different arrangements in the ring of the interacting groups was studied (Table XXVI). The reaction is carried out in boiling pyridine in the presence of catalytic amounts of PhC=CCu (81IZV1342). 4-Acetylenyl-l-methylpyrazole-5-carboxylic acids (Scheme 121) are fully isomerized into the pyranopyrazoles in 20 min in 62-84% yields. 

It is evident that in this ring transformation the C-3-C-4 bond in the pyridine ring has undergone fission. This bond breaking very probable occurs in the covalent o-adduct at C-4. After ring opening the imino-acetylene derivative is formed it is in equilibrium with the iminoketenimine, in which cyclization easily occurs (Scheme 45). 

Some other ring expansions involving the intramolecular amino Claisen rearrangement of vinylarylaziridine [ 123], the Diels-Alder reaction of indoles with acetylene derivative [124-127] and the dibromocarbene insertion into quinoline enol ethers [ 128] have been used to prepare 1-benzazepines. On the other hand, treatment of 3-chloro-3-phenyl-l,2,3,4,5,6-hexahydro-l-benz-azocin-2-ones with piperidine causes a ring contraction to give 2-phenyl-2-(l-piperidinylcarbonyl)-2,3,4,5-tetrahydro-l//-l-bcnzazepines in an excellent yield [23]. 

Aryl acetylenic derivatives continue to exhibit interest as precursors for fused ring systems. Foe example, treatment of l-methyl-5-(trimethylsilylethynyl)uracil with ammonium fluoride leads to 3-methylfuro[2,3- 1pyrimidin-2(3//)-one in good yield <2006JMC391>. 

Transition metal catalyzed insertion reactions offer a convenient route for the preparation of five membered heterocyclic rings. Besides intramolecular Heck-couplings and CO insertion, examples of the intramolecular insertion of an acetylene derivative constitute the majority of this chapter. Although some of these processes involve the formation of a carbon-heteroatom bond, they are discussed here. 

The same strategy was successfully employed in the preparation of the natural product cicerfurane. The procedure started from 4-bromoresorcine and the sesamol-derived acetylene derivative in 3.59.75 One-pot acetyletion, cross-coupling and deprotection followed by spontaneous ring closure led to... 

Not only acetylene derivatives do undergo palladium catalysed intarmolecular carbon-nitrogen bond formation with amines. The similar reaction of olefins in a Wacker-type process also leads to ring closure. (0-Aminopentenes bearing a suitable leaving group in the 4-position were converted to pyrroles in a cyclization-isomerisation-elimination sequence (3.65.),82... 

The insertion of acetylene derivatives might also be utilised in the preparation of six membered rings. A characteristic distinction between such processes and olefin insertion is the fact, that the intermediate formed by the insertion of an acetylene into the palladium-carbon bond is unable to undergo /2-hydride elimination, therefore the concluding step of these processes is usually reductive elimination. 

Pattenden and Schulz have reported that treatment of the acetylene derivative 43 with (TMS)3SiH leads, in one pot, to the bicyclic compound 44 in 70% yield (equation 71)". The proposed mechanism involves (TMS)3Si radical addition to the triple bond to form a vinyl radical followed by a remarkable cascade of radical cyclization-fragmentation-transannulation-ring expansion and termination via ejection of the (TMS Si radical to afford the bicyclic product. 

Cyclocondensation of 3-diethylamino-5-phenylethynyl-l,4-naphthoquinone with hydrazine resulting in the closure of a pyridazine ring is reported. This hydrazine condensation was unknown for peri-acetylenic derivatives of polycyclic quinones <2000TL771>. 

As found a few years ago [71], acetylenes that can be traced back to the diethynylbenzenes 45 and 47 are useful starting materials for the preparation of cyclophanes that possess triple bonds and triple-bond derived functionalities in their molecular bridges. Compared to cyclophanes bearing functional groups in benzene ring positions, relatively little is known about bridge-functionalized cyclophanes. That these - and especially acetylenic derivatives -have considerable potential in synthetic aromatic chemistry will be shown below. 

Medium-ring acetylenes (8- to 11-membered) with one triple bond are isolable compounds. Eight- and ten-membered cyclic acetylenes containing more than one unsaturated bond have been prepared and isolated. Isolable substituted cycloheptyne derivatives will also be discussed in this section. 

Tsu]i, J. Ring-closing metathesis of functionalized acetylene derivatives a new entry into cycloalkynes. Chemtracts 1999,12, 522-525. 

With regard to their classification, we will distinguish four series of unsaturated derivatives the vinyl series, the allyl series, the acetylenic series, and the ring-unsaturated derivatives that are bioisosteric to aromatic rings. 

Stereoselective 1,3-dipolar cycloaddition of the azomethine imine 283, obtained by reacting acetaldehyde and the dihydropyrazolo[4,3-d]-pyridazin-4-one 282, with the acetylenic derivative 284 resulted in the construction of the second fused pyrazole ring of 285. Condensation of 282 with the dialdoglucopyranose 286 instead of acetaldehyde gave the aldose azomethine imine 287, which added 284 to give the C-nucleoside 288 carrying two carbohydrate moieties (93FA231) (Scheme 87). 

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