Catalysis alkynes

Keywords Palladium Catalysis Alkyne Heterocycle Carbocycle... 

In the same catalysis, alkyne trimerization was also possible, albeit in low yield. The choice of monoyne was important 4-octyne selectively gave a para-cyclophane, but dimethyl acetylenedicarboxylate (DMAD) gave an ortho cycloadduct, which is not cyclophane (Scheme 8.10) [7b]. 

Khan, M. M. T. 1974, Homogeneous Catalysis by Metal Complexes, Vol. II, Activation of Alkenes and Alkynes, Academic Press New York - London... 

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

The cyanosilylation of alkynes with trimethylsilyl cyanide proceeds by either Pd or Ni catalysis to give 182[99]. When an excess of trimethylsilyl cyanide is used, the 5-aminopyrrole-2-carbonitrile 183 is obtained[100,101]. 

Stereoselective and chemoselective semihydrogenation of the internal alkyne 208 to the ew-alkene 210 is achieved by the Pd-catalyzed reaction of some hydride sources. Tetramethyldihydrosiloxane (TMDHS) (209) i.s used in the presence of AcOH[116]. (EtO)3SiH in aqueous THF is also effective for the reduction of alkynes to di-alkenes[l 17], Semihydrogenation to the d.v-alkene 211 is possible also with triethylammonium formate with Pd on carbon[118]. Good yields and high cis selectivity are obtained by catalysis with Pd2fdba)3-Bu3P[119],... 

Sulfonyl bromides and iodides react similarly217-218-225 copper-salt catalysis in these cases facilitates the additions but is not absolutely necessary however, it influences the stereochemistry of the additions. Addition of sulfonyl iodides226 as well as the uncatalyzed thermal addition of sulfonyl bromides227 to alkynes leads to an exclusive trans-addition, whereas CuBr2 catalysis in the latter case causes the formation of cis-addition products to some extent (11 16%) correspondingly, copper-salt catalysis in sulfonyl chloride additions to alkynes leads to the formation of a mixture of Z,E-isomers228-229 (equation 40). 

ALKYL-l-ALKYNES, 58, 1 ALKYL ARYL SULFIDES, 58,143 Alkyl aryl thioethers, 58,145 Alkylation, enolates, 56, 52 C-ALKYLATION, phase transfer catalysis... 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Homc eneous Catalysis 4.5.2.1 Activation ofthe Alkyne... 

A variety of transition metal complexes catalyze hydrosilylation of alkynes. Catalysis of hydrosilylation by rhodium gives T -alkenylsilanes from 1-alkynes.74... 

Recently, Pal et al. found that (.S )-prolinol could facilitate the coupling reaction of terminal alkynes with 3-iodoflavone under palladium-copper catalysis in aqueous DMF to give 3-alkynyl substituted flavones of potential biological interest (Eq. 4.17). The coupling of iodobenzene with terminal alkynes at room temperature in water without any cosolvent was completed within 30 minutes, affording the desired product in good yield.36... 

Although the titanium-based methods are typically stoichiometric, catalytic turnover was achieved in one isolated example with trialkoxysilane reducing agents with titanocene catalysts (Scheme 28) [74], This example (as part of a broader study of enal cyclizations [74,75]) was indeed the first process to demonstrate catalysis in a silane-based aldehyde/alkyne reductive coupling and provided important guidance in the development of the nickel-catalyzed processes that are generally more tolerant of functionality and broader in scope. 

We are applying the principles of enzyme mechanism to organometallic catalysis of the reactions of nonpolar and polar molecules for our early work using heterocyclic phosphines, please see ref. 1.(1) Here we report that whereas uncatalyzed alkyne hydration by water has a half-life measured in thousands of years, we have created improved catalysts which reduce the half-life to minutes, even at neutral pH. These data correspond to enzyme-like rate accelerations of >3.4 x 109, which is 12.8 times faster than our previously reported catalyst and 1170 times faster than the best catalyst known in the literature without a heterocyclic phosphine. In some cases, practical hydration can now be conducted at room temperature. Moreover, our improved catalysts favor anti-Markovnikov hydration over traditional Markovnikov hydration in ratios of over 1000 to 1, with aldehyde yields above 99% in many cases. In addition, we find that very active hydration catalysts can be created in situ by adding heterocyclic phosphines to otherwise inactive catalysts. The scope, limitations, and development of these reactions will be described in detail. 

Since Bruce s pioneering work in the area of ruthenium vinylidene chemistry (1), it has been well known that isomerization of a terminal alkyne to a vinylidene on a metal center is not only favorable but also effects a reversal in the reactivity of the carbon atoms. However, hydration catalysis was not possible, because alkyl migration from a proposed acyl intermediate led to an... 

Fiirstner and coworkers developed a new Pt- and Au-catalyzed cycloisomerization of hydroxylated enynes 6/4-141 to give the bicylo[3.1.0]hexanone skeleton 6/4-143, which is found in a large number of terpenes [317]. It can be assumed that, in the case of the Pt-catalysis, a platinum carbene 6/4-142 is formed, which triggers an irreversible 1,2-hydrogen shift. The complexity of the product/substrate relationship can be increased by using a mixture of an alkynal and an allyl silane in the presence of PtCl2 to give 6/4-143 directly, in 55 % yield (Scheme 6/4.36). 

Ethyl diazopyruvate, under copper catalysis, reacts with alkynes to give furane-2-carboxylates rather than cyclopropenes u3) (Scheme 30). What looks like a [3 + 2] cycloaddition product of a ketocarbenoid, may actually have arisen from a primarily formed cyclopropene by subsequent copper-catalyzed ring enlargement. Such a sequence has been established for the reaction of diazoacetic esters with acetylenes in the presence of certain copper catalysts, but metallic copper, in these cases, was not able to bring about the ring enlargement14). Conversely, no cyclopropene derivative was detected in the diazopyruvate reaction. 

As with carboxylic acids obtained by palladium hydroxycarbonylation, their derivatives esters, amides, anhydrides and acyl halides are synthesized from alkenes, CO and HX (X = OR, NR2 etc.). The Pd-catalyzed methoxycarbonylation is one of the most studied reactions among this type of catalyzed carbonylations and has been reviewed and included in reports of homogeneous catalysis.625, 26 The methoxycarbonylation has been applied to many different substrates to obtain intermediates in organic syntheses as well as specific products. For instance, the reaction has been applied for methoxycarbonylation of alkynes666 Highly efficient homogeneous Pd cationic catalysts have been reported and the methoxycarbonylation of alkynes has been used to develop economically attractive and environmentally benign process for the production of methyl... 

---