1-Trimethylsilyl-1-alkynes

HydromagnesiatUm vinylsilanes. The hydromagnesiation (10, 130-131) of 1-trimethylsilyl-1 -alkynes with isobutylmagnesium bromide followed by alkylation affords (Z)-l,2-dialkylvinylsilanes in high yield. 

In a preliminary work toward the dynemycin A antitumor antibiotic, AgOTf in a stoichiometric amount in refluxing 1,2-dichloroethane was able to assist the addition of 1-trimethylsilyl-1-alkynes to iV-acylated quinolines (eq 57). ... 

In an effort to identify a more stereoselective route to dihydroagarofuran (15), trimethylsilylated alkyne 17 was utilized as a substrate for radical cyclization (Scheme 2). Treatment of 17 with a catalytic amount of AIBN and tri-n-butyltin hydride (1.25 equiv) furnishes a mixture of stereoisomeric vinyl silanes 18 (72% combined yield) along with an uncyclized reduction product (13% yield). The production of stereoisomeric vinyl silanes in this cyclization is inconsequential because both are converted to the same alkene 19 upon protodesiiyiation. Finally, a diastereoselective di-imide reduction of the double bond in 19 furnishes dihydroagaro-... 

Phenylation of terminal alkynes took place with Ph3BiF2 in the presence of Cu(I) chloride (Scheme 10) [26], Trimethylsilyl alkynes similarly worked as terminal alkynes. Other pentavalent organobismuth compounds such as Ph3BiC03 and Ph3BiCl2 were much less efficient than Ph3BiF2. Biphenyl was also formed as a by-product. It was proposed that the products were formed through reductive elimination of the intermediate Ph3Bi(C=CR1)2. 

Ishikawa and coworkers have studied the unique reactivity of strained cyclic disilanes (Equation 9.11) [35]. Transition metals, especially those of Group 10, readily insert into the Si—Si bond of disilacyclobutene 118 and can catalyze the addition of that bond across a variety of unsaturated acceptors. In the case of Ni(0)-catalyzed reactions of 118 with trimethylsilyl alkynes, insertion was found to occur both in a 1,2-and in a 1,1-fashion. The latter of these pathways implies a 1,2-silyl-migration, presumably occurring at the metal center. A nickel vinylidene intermediate was therefore proposed, though efforts to prove its existence were inconclusive. Similar vinylidene intermediates have been proposed by Ishikawa and coworkers to account for migrations observed in related palladium- and platinum-catalyzed reactions [36]. 

Corey introduced the use of a 1 1 CsF/CsOH salt to effect the in-situ activation of trimethylsilyl alkyne and subsequent addition to aldehydes (Eq. 2) [8]. The use of catalytic quantities of CsOH to effect the addition of terminal acetylenes to ketones in DMSO/THF or THF has also been documented (Eq. 3) [9]. 

Diynes 6, which consist of a trimethylsilyl alkyne tethered to a tertiary propargyl alcohol, undergo ruthenium catalyzed cycloisomerization in aqueous acetone to form the dienone intermediate 7. Concomitant electrocyclization affords 2-trimethylsilyl-2-//-pyrans in high yield (Scheme 3) <2004OL4235>. 

The incorporation of propyne and 1-hexyne into alkynyliodonium salts with HTIB and its mesyloxy analog has been accomplished with the aid of a silica bead desiccant (equation ll)5,6, but the yields of the products are low. A better method for the synthesis of alkynyliodonium tosylates in which R is a linear alkyl group entails the treatment of (trimethylsilyl)alkyne/iodosylbenzene mixtures in chloroform with boron trifluoride etherate. When aqueous sodium tosylate is added to the resulting solutions, alkynyliodonium tosylates are produced and can be isolated from the organic phase (equation 12)7. The... 

Terminal alkynes are not the only reaction partners. 1-Trimethylsilyl alkynes (R—C=C SiMe3) give the diyne R C=C C=C R) upon reaction with CuCl or Cu(OAc)2/Bu4NF. ... 

Analogously, (trimethylsilyl)alkynes and (trimethylsilyl)propanoates can serve as substrates for the preparation of cyclic vinyl silanes. ... 

A general cyclization reaction of 6-lithiated (trimethylsilyl)alkynes is exemplified by the conversion of the iodo compound 499 into the methylenecyclopentane 500 by treatment with -butyllithium . Heating a mixture of the acetylenic silane 501 and 2-(benzyloxymethyl)allylzinc bromide 502 resulted in the diene 503, which cyclized to the methylenecyclopentene 504 in the presence of tetrakis(triphenylphosphine)palladium ... 

One-pot Darzens-desilylation reaction of trimethylsilyl alkynals is efficiently realized under PTC conditions (eq. 65). 

Ethynylaniline. See the general procedure for the deprotection of trimethylsilyl alkynes. The compounds used were 4-... 

To a suspension of polymer-supported aryl(trimethylsilyl)alkyne 28 (23.96 g) and THF (9 mL/g of polymer) in an Erlenmeyer flask was added a solution of TBAF (50 mL, 50 mmol, 1.0 M in THF). The suspension was swirled periodically for 25 min. The polymer was then transferred to a preweighed flitted filter using THF, washed sequentially (ca. 30 mL/g polymer) with THF followed by CH3OH, and dried to constant mass in a vacuum oven at 60 °C for 36 h to give desired polymer beads 22.11 g. IR 3317, 2106 cm. ... 

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

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]. 

The Pd(0)-catalyzed addition of trimethylsilyl iodide to an alkyne, followed by capture with alkynylstannane, affords the stereo-defined enyne 186. The reaction is explained by the oxidative addition of iodosilane, the insertion of an alkyne to generate the vinylpalladium 185, and the capture of 185 with the alkynylstannane 184[102]. 

With the exocyclic alkylidene at C-13 properly in place, the elaboration of the l,5-diyn-3-ene moiety can now be addressed. Cleavage of both acetate and trimethylsilyl functions in 86 with basic methanol, followed by triethylsilylation of the newly formed tertiary hydroxyl group, efficiently affords alkyne 25 (86 % overall yield). This substance was regarded as a viable candidate for a Pd-catalyzed coupling reaction.12 Indeed, treatment of 25 with (Z)-chloroenyne 26 in the presence of a catalytic amount of Pd(PPh3)4 and Cu1 results in the formation of enediyne 24 in 91 % yield. 

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

Finally, sulfoxides containing an a-carbonyl group and a f)-syn trimethylsilyl group [28-30], for example 1208 or 1211, are, on heating, readily converted to alkenes such as mesityl oxide 1209 and the alkyne 1212, and to trimethylsilyl phe-nylsulfenate 1210 [29, 30] (Scheme 8.11). 

Several ways to suppress the 2-oxonium-[3,3]-rearrangements might be envisioned. Apart from the introduction of a bulky substituent R at the aldehyde (Scheme 23) a similar steric repulsion between R and R might also be observed upon introduction of a bulky auxiliary at R. A proof-of-principle for this concept was observed upon by using of a trimethylsilyl group as substituent R in the alkyne moiety (Scheme 25, R = TMS). This improvement provided an efficient access to polysubstituted dihydropyrans via a silyl alkyne-Prins cyclization. Ab initio theoretical calculations support the proposed mechanism. Moreover, the use of enantiomerically enriched secondary homopropargylic alcohols yielded the corresponding oxa-cycles with similar enantiomeric purity [38]. 

Under the conditions of the Wacker oxidation, 4-trimethylsilyl-3-alkyn-l-ols give 7 -lactones. Similarly, A-carbamoyl or A-acetyl 4-trimethylsilyl-3-alkynamines cyclize to y -lactams. Formulate a mechanism for these reactions. (Hint In DzO,... 

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