Silylacetylenes

Diketones. The Sharpless procedure for oxidation of alkenes with NaIO catalyzed by Ru02 (11,462-463) is equally efficient for oxidation of alkynes to 1,2-diones. In fact, alkenes and alkynes react at a similar rate, but ether, epoxide, and ester groups are stable to the reagent. A 1-silylacetylene is oxidized to an acylsilane. Yields are moderate to high.1... 

Diethynylallenes, i.e. derivatives of the parent system 8 in Scheme 5.1, are obtained when the propargylic substrate already contains an additional triple bond as shown in Scheme 5.14. Here the bispropargyl carbonate 107 - for example with R = n-hexyl - is coupled with tris(isopropyl)silylacetylene to provide the protected hydrocarbon 108 in excellent yield (94%) [39, 40]. 

Scheme 16.95 Cross-coupling reaction of a terminal allene and silylacetylene.

The C-glycosylation of pentose glycals with silylacetylenes or allylsilanes through oxocarbenium ion intermediates proceeds with high regio- and stereo-selectivity, giving the 1,4-anti compounds as the main products. ... 

By contrast, the isomerization of silyl olefins and addition of silylacetylenes =C—H bond into imines catalyzed by iridium complexes appears to serve as a suitable route for the synthesis of silylfunctionahzed organic compounds. Hence, the acquisition of experimental data on catalysis by iridium complexes in silicon chemistry may be regarded as an initial stage in the quest for catalytic processes leading to the synthesis of other p-block (e.g. B, Ge, Sn, P)-carbon bond-containing compounds. 

Acetylene-vinylidene rearrangements of silylacetylene-iron carbonyl complexes have been observed,537 while iron-acetylide hydride complexes of the type [Fe(H)(C=CR)(dmpe)2], where dmpe=l,2-bis(dimethylphosphino)ethane, have been found to react with anions to afford substituted alkenyl complexes. It has been proposed538 that a likely reaction course for this latter rearrangement involves initial protonation of the cr-bound acetylide ligand at the carbon (I to the metal centre to form a vinylidene complex. Metal-to-carbon hydride migration in this vinylidene complex with attack by the anion would then lead to the neutral complex (see Scheme 106). A detailed mechanistic investigation has been carried out539 on the novel metathetical... 

An unexpected rearrangement was observed during studies directed towards the synthesis of bicyclic keto silanes by the thermal rearrangement of cycloalkanones bearing an co-silylacetylenic chain P to the carbonyl group. Thus, the bicyclic enol silyl ether 2 was formed in 60-65% yield when the ketone 1 was heated neat at 300°C for 2 hours. 

Sulfoxide elimination of the arylthio group of 5, deprotection of the silylacetylene (KF), acetal hydrolysis (CSA in CH3CN-H20), and silylation of the free hydroxyl group provides the aldehyde 6 in 80% overall yield from 5. On treatment with LiN[Si(CH3)3]2 and CeCl3 (3 equiv.) in THF at 0°, 6 cyclizes to 7, obtained as a... 

Mayor et al. [13g] prepared the iodide 2 via substitution of the fluoride 18 by using sodium fcrt-butylthiolate (Scheme 10.5). A cross-coupling reaction with trimethyl silylacetylene generated the alkyne 19 that was desilylated by tetrabutylam-monium fluoride finally to provide 5. 

FIGURE 6. Examples for comparison of molecular state data based on first and second order perturbation (a) Correlation of the vertical 7r-ionization energies of heterobenzenes C5H5X36 with atomic ionization energies of elements X allowing a correct prediction for silabenzene15 37 and (b) second order perturbation in silylacetylene as visualized by its (helium I) photoelectron spectrum... 

Heteroaromatic ketones (Eq. 60) [101] and enones (Eq. 61) [103] with an activated olefinic C-H bond have also been found to undergo effective coupling with l-phenyl-2-silylacetylene. 

Silylacetylenes were reported to undergo cross-coupling with internal alkynes (Eq. 65) [109]. 

Fully substituted triazoles were synthesized via the four-component coupling reaction of the unactivated silylacetylenes 50, two equivalents of allyl carbonates 5b, and trimethylsilyl azide 42 in the presence of a Pd(0)-Cu(I) bimetallic catalyst (Scheme 18) [54], Various trisubstituted 1,2,3-triazoles were obtained in good yields. The reaction most probably proceeds through the formation of alkynylcopper species 52, which on cross-coupling reaction with the 7r-allylpalladium complex 53 gives the products 51. 

Silver(I)-catalyzed cyclizations of substituted allenes to heterocydic ring systems induding 2,5-dihydropyrroles have been described previously [4,10]. Moreover, sil-ver(I) salts are known to form stable rr-complexes with terminal acetylenes [11]. On the other hand, on treatment with silver nitrate silylacetylenes were reported to afford silver acetylides [12]. Based on these considerations and additional experimental evidence [5,13], the following mechanism has been proposed forthe sUver(I)-mediated oxidative cydization of homopropargylamines to pyrroles ]5] (Scheme 15.3). 

ShaCK, Jean TS, Wang DC (1990) Intramolecular Radical Cyclization of Silylacetylenic or Olefinic a-Iodo Ketones Application to the Total Synthesis of ( )-Modhephene. Tetrahedron Lett 31 3745... 

The 1,4-diketone (54) was prepared by the titanium-catalyzed butenylation of the silylacetylene (51). followed by the oxidations of the termini double bond in (52) to give (53) and the silylated double tend (Scheme 14). ... 

Also silylacetylenes imdergo self-polymerization under hydrosilation conditions to give high molecular weight polymers (equation 19). ... 

In a cross-coupling reaction of 3- or 4-chloropyridazines and trimethyl-silylacetylene in the presence of Pd(PPh3)2Cl2-CuI as catalyst, the tri-methylsilyl derivatives were obtained (82S312). The same transformation with monosubstituted acetylenes afforded 3-alkynylpyridazines or their... 

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