Termination catalysed reactions

A seven-membered ring is formed in the cyclization of 195 (equation 95)105. The homologue 196 affords the fused cyclooctane 197, together with the cis- and trans-decalinones 198 (equation 96)106. Six-, seven- and eight-membered rings are produced in Lewis acid-catalysed reactions of various cyclohexenones with side-chains terminating in allylic trimethylsilyl groups (equations 97 - 99)107. 

Terminal alkynes are converted in high yield (70-80%) into 1-iodoalkynes by their copper-catalysed reaction with iodine under phase-transfer catalytic 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. 

In an interesting catalysed conversion of trichloroethene by secondary amines into aminoacetamides, the initial steps are thought to involve the p-elimination of HC1 to produce dichloroethyne (Scheme 9.1), which reacts with the secondary amine under the wet conditions to produce the amide [35] the reaction does not work with N-alkylanilines. Such a mechanism is realistic, as it is well known [36] that trichloroethene is converted into the inflammable and explosive dichloroethyne by bases, and quaternary ammonium salts catalyse the formation of the alkyne when trichloroethene is reacted with oxiranes [37]. Chloroethynes have also been obtained by the catalysed reaction of terminal ethynes with carbon tetrachloride under basic conditions [38]. 

Sulfur trioxide is a strong Lewis acid comparable in strength with such acids as GaCl3, BC13j and, according to some data, even SbCl5 [4]. Non-catalysed reaction of S03 with terminal polyfluoroalkenes results in formation of /J-sultones, which is currently viewed as a concerted electrophilic 2 + 2 cycloaddition reaction [4], This process has been intensively studied for over 30 years and data on this reaction has been reviewed [173]). 

Termination of the Metal-promoted or -catalysed Reactions and a Catalytic Cycle... 

As another example of the reaction via the ruthenacyclopentene, 1,4-diketones are formed by the Ru-catalysed reaction of terminal alkynes with vinyl ketones in aqueous DMF in the presence of NH4PF6 and InCl3. The reaction is explained by the generation of the ruthenacyclopentene 422, followed by addition of H2O to the double bond. Elimination of /5-hydrogen and reductiuve elimination afford 1,5-diketones [165a],... 

A stereoselective synthesis of substituted tetrahydrofurans (69) via Pd-catalysed reactions of aryl and vinyl bromides with y -hydroxy terminal alkenes (68) has been described. This transformation affords trans-2,5- and frara-2,3-disubstituted tetrahydrofurans with up to >20 1 dr. This methodology also provides access to bicyclic and (g) spirocyclic tetrahydrofuran derivatives in good yield with 10-20 1 dr. The effect of... 

El and Es are known (see above) and must be very small, so 12 = 23.5 kcal. mole- (the value 28.6 kcal given by Kalb and Allen appears to be incorrect). Hence reaction (84) is quite slow, and the steady-state concentration of sulphate radical-ions relatively high. This would account for reaction (66) being favoured as the chain-termination step, rather than reaction (77), the dominant termination step in the silver ion-catalysed reaction. 

The rhodium-catalysed reaction between 1,3-azoles and terminal alkenes is thought to proceed via a carbene complex. ... 

Palladium-catalysed reactions of iodocubane with terminal alkynes yielded the corresponding alkynylcyclooctatetraenes rather than the desired alkynylcubanes. An alkynylcubane, compound 164, was obtained from methyl 4-iodocubyl ketone (163) by the procedure just described. 

The cyclopalladated Schiff s base 624 reacts with symmetrical alkynes RC=CR [R = Et, C02Me or (EtO)2CH] to give isoquinolinium salts 625 . 2-Phenylcinnolinium salts 627 are similarly formed from the palladium complex 626 and acetylenes k Palladium-catalysed reactions of c -bromo- or o-iodoaniline with terminal alkynes under carbon monoxide pressure give good yields of 4-quinolones (equation 62). ... 

The disylanylstannane 635 adds terminal alkynes regio- and stereoselectively to form (Z)-alkenes 636, which undergo a tetrakis(triphenylphosphine)palladium-catalysed reaction with phenylacetylene to give 1 -sila-4-stannacyclohexa-2,5-dienes 637. 1,4-Dithianes 639 ( = 1) and 1,4-dithiepanes 639 n = 2) are obtained by the azoisobutyronitrile - induced homolytic cycloaddition of alkynes R C=CR (R = Pr, Bu or CMe20H R = H or Pr) to the dithols 63836 7a b. 

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