Diynes halogenation

The 14-electron species denoted here as Cp2M (M = Ti, Zr), generated from Group 4 metallocenes, mediate useful oxidative cyclizations of dienes 231 [103,104], enynes 233 [105] and diynes 235 [105,106] via the metallacycles 232, 234 and 236. These metallacycles are useful intermediates, which are hydrogenolysed, carbonylated, halogenated, attacked by electrophiles and converted to functionalized cyclic compounds such as 238 and 239 [107],... 

An additional functional group may be present in one of the reactants. Alkylation of vinylacetylene gives low yields of l-alken- ynes. - Cuprous halide catalyst is required for alkylations by allyl bromide the yields of l-alken-4-ynes are about 88%. Both halogen atoms of dibromides can be induced to take part in alkylation if the halogens are not on the same or adjacent carbon atoms. The yields of diynes are 46-85%. Diynes in... 

With monosubstituted diynes, addition occurs predominantly at the terminal triple bond, although the selectivity depends on the nature of the halogen and the substituent . The dichloro derivatives 178a and 178b were obtained in a 3 1 ratio from the reaction of chlorine with excess 1,3-pentadiyne at —40 °C. In spite of the fact that a two-fold excess of pentadiyne was used, tetra- and higher polychlorides... 

Addition of hydrogen halides to conjugated diynes occurs very slowly, and unlike the behaviour in halogen addition, the rate decreases with increasing number of triple bonds . 2,4,6,8-Decatetrayne fails to react with HBr even under fairly drastic conditions. Because of the low rate of the initial addition, polyhalogenated products often predominate over monoadducts. 

Several derivatives of the halogenodiacetylenes 118 and 119 have been prepared from the corresponding terminal diynes by the metalation/halogenation approach [85, 86], and their preparative use will be described below. Finally, calculations have been published on l-cyano-4-iodobutadiynes to assess the use of these systems as model compounds for push-pull polyynes, which in turn are of interest in connection with organic nonlinear optical materials [87]. 

Generally, homocoupling of aryl and alkenyl halides has been the most widespread. Other halide derivatives, such as alkyl or alkynyl halides, have seldom been used. This is either because of problems during homocoupling (alkyl halides may easily undergo dehydro-halogenation) or because the homocoupled product (diynes) could be obtained by more convenient methods. Nonetheless, a rare example of homocoupling of alkyl halides catalyzed by palladium chloride in the presence of hydrazine as the reductant was published " however, this procedure is of limited synthetic value (Scheme 2). 

The reactivity of butadiene and -diyne derivatives in layer perovskites demonstrates the suitability of these complex salts to act as templates for solid state reactions. Besides the polyaddition also other chemical reactions should be able to occur with a high stereoselectivity, as for example isomerizations, or addition reactions, such as hydrations, halogenations, oxidations, or polycondensations. In any case it will... 

Cyclization of l-Silyloxy-l,5-diynes. A HNTf2-promoted 5-endodig cycXizdtion of l-siloxy-l,5-diynes has been shown to give highly selective 5-halo enones by abstraction of a halogen from halocarbons in good yields (eq 14). ... 

A variety of symmetrical and unsymmetrical 1,3-diynes underwent double trans hydrosilylation with silafluorene to furnish spirocyclic siloles (Table 20.4). A range of heteroatom functionalities, including halogens, silicon, and boron, on the phenyl rings survived unscathed under the reaction conditions. l-Phenyl-4-(4-vinylphenyl)buta-1,3-diyne furnished the corresponding silole with the vinyl group remaining intact. 

One year later, they discovered that Tf2NH promoted 5-endo-dig cyclization of l-siloxy-l,5-diynes, which results in the concomitant formation of carbon-halogen bonds as a result of halide abstraction from haloalkane (CHCI3, CH2Br2, CH2CI2, Mel) by intermediate alkenyl cation to afford P-halo enones as a single alkene isomer dr > 97 3) (Table 2.11) [23]. Interestingly, the use of either CSA or anhydrous HCl resulted in the formation of alternative reaction products. 

The reaction tolerates a wide range of functional substituents and allows use of alkenes, alcohols, amines, esters, halogens, and nitriles. Reactions of 1,6-octadiynes with such monoynes results in ortho- and mefia-substituted derivatives. Regioselectivity of the reaction is controlled by the choice of the ligand. Thus, the interaction of diyne 2.10 and monoyne 2.11 in the presence of dppe [l,2-bis(diphenylphosphino)ethane] yields mainly the meta-isomer 2.12 (selectivity 88%), whereas in the presence of dppf [1,1 -bis(diphenylphosphino)ferrocene] the yield of ortho-isomerlA3 reaches 82% [39] (Scheme 2.5). 

Another pathway, which does not require activation, is based on nucleophilic halide anion attack on an enediyne to afford the aryl halide [335]. Thus, cyclodeca-l,5-diyne-3-ene 3.720 in the presence of lithium halide and a weak acid produces 1-halotetrahydronaphthalene 3.723. Kinetic data show that the rate determining step of the cyclization is the formation of para-henzyne diradical 3.721. Then fast addition of halide anion occurs leading to the generation of the haloaryl anion 3.722, X = Cl, Br, I, or the corresponding aryllithium, which is protonated to form 1-halogenated 5,6,7,8-tetrahydronaphthalene 3.723 (Scheme 3.81). 

A facile electrocyclization cascade has been reported to occur when diynes (46) are halogenated with NBS or NIS in the presence of a catalytic amount of AgBp4 (Scheme 3). The initial attack by X+ apparently generates the vinylic cation (47) that undergoes cyclization via (48) to produce the benzylic alcohol (49). The silver(I) catalyst then promotes aromatization with a concomitant hydration, giving rise to the halo-substituted benzo[a]fluorenols (50). ... 

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