Acetylene arylation

Branched phenylacetylene monomers can be used to construct dendrimers on supports. This was accomplished using a triazene tether as a focal point, the reaction triad outlined above, and an ABj monomer, as seen in Scheme 7. As in similar solution-phase convergent dendrimer syntheses, the first step was to prime the periphery of the dendrimer with r-butyl groups by di-coupling of a triazene-tethered dibromoaryl monomer with (di-i-butyl-phenyl)acetylene. In this and all subsequent coupling steps, an excess amount of the monodendron acetylene was used to drive the reaction to completion. The reagents and catalysts were washed away and the excess monodendron was recovered. At the end of the first step, the tri-aryl dendron I-M3-(i-Bu)4 was cleaved from the support (M represents the dendritic monomer unit). Two equivalents of this product were then coupled with the triazene-tethered di-acetylene aryl monomer to produce the heptaaryl dendron I-M7-(/-Bu)g. 

The potassium lithium salt of the aryl acetylene 170 was converted to a di-Grignard reagent with magnesium bromide [Eq. (75)]. Subsequent reaction of 170 with iodine and acidification afforded the acetylenic aryl iodide 171 [140]. 

All other cross-couplings involving terminal alkynes and halo amides have involved ring closure on nitrogen. Thus, o-halobenzamides react with simple terminal alkynes in the presence of a Pd/Cu catalyst to afford either (Z)-3-aryl(alkyl)idene isoindolin-l-ones or the corresponding 2-(l-alkynyl)benza-mides, which are readily cyclized by NaOEt/EtOH or Pd(OAc)2 catalyst to give isoindolin-l-ones (Eq. 11) [35,36]. When acetylenic aryl carbinols are employed as the alkynes, 3-(acylmethyl)isoindolin-l-ones are obtained instead (Eq.l2) [37]. 

Ynones 17 can be generated in situ in a Pd-catalyzed carbonylati ve coupling reaction with aryl halides, which has been extended to a one-pot four-component synthesis of pyrazoles 18 (R = aryl) from terminal acetylenes, aryl iodides, hydrazine hydrate, and Mo(CO)6 (as CO donor) in the presence of CS2CO3 and Pd(OAc)2/CuI as catalyst system [435]. 

C-C double bond cleavage of an enyne derivative using a metallocene derivative was reported by Takahashi and coworkers [34]. When an alkyne was treated with Cp2ZrEt2 and vinyl bromide or vinyl ether in this order after hydrolysis a 2,3-disubstituted diene derivative was obtained (Eqs. 22 and 23). Bis-silyl acetylene, aryl-substituted acetylene or cyclohexyl-substituted alkyne could be used as internal alkynes. 

Aryl-S02Cl. At present only a few data concerning electrophilic 1,3-substitution with allenic and acetylenic tin or silicon compounds are available. 

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

Alkynes with EWGs are poor substrates for the coupling with halides. Therefore, instead of the inactive propynoate, triethyl orthopropynoate (350) is used for the coupling with aryl halides to prepare the arylpropynoate 351. The coupling product 353 of 3,3-dicthoxy-l-propyne (352) with an aryl halide is the precursor of an alkynal[260]. The coupling of ethoxy) tributylstan-nyl)acetylene (354) with aryl halides is a good synthetic method for the aryl-acetate 355[261]. 

When aiomatics aie present, they can capture the intermediate vinyl cation to give P-aryl-a,P-unsatutated ketones (182). Thus acylation of alkyl or aryl acetylenes with acyhum salts in the presence of aromatics gives a,P-unsaturated ketones with a trisubstituted double bond. The mild reaction conditions employed do not cause direct acylation of aromatics. 

Isoxazole-3-carbaldehyde has been obtained as a minor product from the reaction of acetylene with a mixture of nitric oxide and nitrogen dioxide (61JOC2976). Although 3-aryl-4-formylisoxazoles have been synthesized in good yields from the reaction of benzonitrile Af-oxides with 3-(dimethylamino)-2-propen-l-one (71S433), the parent member of the series, isoxazole-4-carbaldehyde, has never been reported. It may possibly be obtained by the addition of fulminic acid to 3-(dimethylamino)-2-propen-l-one. 

Hydrogen chloride adds to aryl acetylenes in acetic acid to give mixtures of a-... 

The copper species formed depends on the solvent, and three different species were detected by F NMR, although the structure of each species was not elucidated [245 This copper reagent undergoes a variety of coupling reactions with aryl, alkenyl, allyl, and acetylenic halides [244, 245 (equation 162)... 

The above cycloaddition process consists of two separate [3-1-2] cycloaddition steps and represents a 1,3-2,4 addition of a multiple bond system to a hetero-1,3-diene [7S7]. The structure ot the azomethine imine intermediate has been proved unequivocally by X-ray analysis [195] Ethylene [194], acetylene [/iS2] . many alkyl- and aryl- as well sgemmal dialkyl- and diaryl-substituted alkenes [196,197, 198, 199], dienes [200], and alkynes [182, 201], certain cyclic alkenes [198, 199,... 

The treatment of LiN(SiMc3)2 with aryl tellurenyl iodides gives stable Ai,iV -bis(trimethylsilyl)tellurenamides that react with acetylenes to give acetylenyl tellurides (Eq. 2.4). 

Aryl amine 31 was found to react readily with acetylene dicarboxylate 32 to yield fumarate 33. Several similar reactions were reported and found to be general. The... 

---