Trialkylsilyl

Since the acetylenic proton is acidic, it often needs to be protected as a trialkylsilyl derivative. It is conveniently deprotected with fluoride ion. 

A trialkylsilyl group can be introduced into aryl or alkenyl groups using hexaalkyidisilanes. The Si—Si bond is cleaved with a Pd catalyst, and trans-metallation and reductive elimination afford the silylated products. In this way, 1,2-bis-silylethylene 761 is prepared from 1,2-dichloroethylene (760)[625,626], The facile reaction of (Me3Si)2 to give 762 proceeds at room temperature in the presence of fluoride anion[627]. Alkenyl- and arylsilanes are prepared by the reaction of (Me3Si)3Al (763)[628],... 

The reaction of hydrosilanes with butadiene is different from other reactions. Different products are obtained depending on the structurelof the hydrosilanes and the reaction conditions. Trimethylsiiane and other trialkylsilanes react to give the I 2 adduct, namely the l-trialkylsilyl-2,6-octadiene 74, in high yields[67-69]. Unlike other telomers which have the 2,7-octadienyl chain, the 2,6-octadienyl chain is formed by hydrosilylation. On the other hand, the 1 I adduct 75 (l-trichlorosilyl-2-butene)is formed selectively with trichlorosilane, which is more reactive than trialkylsilanes[69]. The Reaction gives the Z form stereoselectively[70]. A mixture of the I 1 and I 2 adducts (83.5 and 5.2%) is... 

Alternatively, radiohalogen-labeled compounds may be prepared by way of isotopic labeling from the unlabeled bromo or iodo derivatives by various two-step reaction sequences. Examples include the use of trialkylsilyl synthons as described in References 10—13, and the use of boronic acid synthons as described in References 14 and 15. 

Sulfonation of the aromatic ring of l, 2, 2 -trifluorostyrene below 0 C does not give satisfactory yields with chlorosulfonic acid or a sulfur trioxide-dioxane complex Tar forms on heating In contrast, under similar conditions ipso substitution IS facile at the position of a trialkylsilyl or -stannyl group Thus, 4-trimethyl-silyl-T 2, 2 D-trifluorostyrene affords the corresponding trimethylsilyl sulfonate [20] (equation 9)... 

The ubhty of trialkylsilyl trifluoromethanesulfonates (trialkylsilyl tri-flates) IS also well-known [93, 94,95] The simplest of these reagents, tnmethylsilyl tnflate, may be prepared in high yield by the treatment of hexamethyldisiloxane with tnfhc anhydnde [96] (equation 77)... 

Trimethylsilyl trifluoromethanesulfonate (trimethylsilyl triflate) is the most synthetically useful representative of the family of trialkylsilyl perfluoroalkane-sulfonates (for a review, see reference 101) This reagent is commercially available or can be prepared easily by the reaction of chlorotrimethylsilane and triflic acid [101] It has wide application in organic synthesis as an excellent silylating reagent... 

These groups, along with a number of other trialkylsilylethyl derivatives, were examined for protection of phosphorothioates. Only the phenyl-substituted silyl derivative was useful, because simple trialkylsilyl derivatives were prone to acid-catalyzed thiono-thiolo rearrangement. Other trialkylsilylethyl derivatives also suffer from inherent instability upon storage,but the trimethylsilylethyl group has been used successfully in the synthesis of the very sensitive agrocin 84 and for intemucleotide phosphate protection with the phosphoramidite approach. 

In addition to the synthesis of heterocycles, the Corey-Chaykovsky reaction bestows an entry to carbocycles as well. The reaction of (trialkylsilyl)vinylketene 89 with substituted ylide 90 led exclusively to rrans-4,5-dimethyl cyclopentenone 91. The substituted ylide 90 here serves as a nucleophilic carbenoid reagent in the formal [4 +1] annulation reaction. 

A multitude of 1,4-dicarbonyls (1) undergo the Paal-Knorr reaction with and ranging from H to alkyl, aryl, carbonyl, nitrile, and phosphonate, while R and R vary between H, alkyl, aryl, trialkylsilyl, and O-alkyl. Protic acid catalysts are typically used with sulfuric, hydrochloric, and p-toluenesulfonic acids the most popular. Conversion to the furan takes place either at room temperature or upon heating with reaction times varying from five minutes to 24 hours and yields ranging from 17-100%. 

Method G Highruiri-selecdvity is also observed in the fluoride-catalyzed reacdonof silyl nitronates v/ith aldehydes. Trialkyl silyl nitronates are prepared in good yield from primary nitroalkanes by consecndve treatment v/ith iithiiim dusopropylamide and trialkylsilyl chloride at -78 C in THF. 

Nitro compounds have been converted into various cyclic compounds via cycloaddidon reactions. In particular, nitroalkenes have proved to be nsefid in Diels-Alder reactions. Under thermal conditions, they behave as electron-deficient alkenes ind react v/ith dienes to yield 3-nitrocy-clohexenes. Nitroalkenes c in also act as heterodienes ind react v/ith olefins in the presence of Lewis acids to yield cyclic alkyl nkronates, which undergo [3- 2 cycloaddidon. Nitro compounds are precursors for nitnie oxides, alkyl nitronates, and trialkylsilyl nitronates, which undergo [3- 2 cycloaddldon reacdons. Thus, nitro compounds play important roles in the chemistry of cycloaddidon reacdons. In this chapter, recent developments of cycloaddinon chemistry of nitro compotmds and their derivadves are summarized. 

One of the more common methods of alcohol protection is by reaction with a chlorotrialkylsilane, CI-S1R3, to yield a trialkylsilyl ether, R -O-SilTj. Chlorotrimethylsilane is often used, and the reaction is carried out in the presence of a base, such as tciethylamine, to help form the alkoxide anion from the alcohol and to remove the HC1 by-product from the reaction. 

Compounds 1, which bear in X an electrofugical leaving group, such as trialkylsilyl or diphenylphosphinyl, are of high value for the synthesis of stereochemically homogeneous 1,3-dienes via stereospecific anti or urn elimination. 

Replacement of an aromatic/heteroaromatic proton with a trialkylsilyl group can confer a variety of synthetic advantages. The silyl moiety can mask a potentially acidic proton, and it can be readily removed by electrophiles, normally resulting in a process of ipso desilylation ... 

Trialkylsilyl-oxirane werden mit Cupraten in regio- und stereospezifischer Reaktion mit guten Ausbeuten zu /2-Hydroxy-alkylsilanen1 reduktiv gespalten z.B. ... 

Trialkylsilyl radicals are known to be strongly bent out of the plane (cr-type structure 5). The pyramidal structure of trialkylsilyl radicals (RaSi ) was first indicated by chirality studies on optically active compounds containing... 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Phosphoranyl radicals were observed by FPR at the end of the sixties [91]. For a long time, phosphoranyl radicals, particularly the alicyclic ones [59], were considered as elusive species. However, recently. Marque et al. [92] observed the first strongly persistent (ti/2=45 min at RT) alicyclic phosphoranyl radicals (Fig. 10) when they irradiated bis(trialkylsilyl)peroxides in the presence of tris(trialkylsilyl)phosphites. The increased lifetime of the ensuing phosphoranyl radicals is a consequence of the presence of four bulky R3SiO groups around the phosphorus. The bulkiness of the substituents hampers the dimerization and the Sh2 reaction of phosphoranyl radicals with the peroxide initiator. Furthermore, the high strength of the P-0 and 0-Si bonds results in slow a- and p-scissions [93]. 

It is well known that trialkylsilyl groups are prone to migrate via different types of molecular rearrangements [131]. This behavior serves to explain some... 

The per(silylethynyl)ated octadehydro[12]annulenes 58a, b and the dodecade-hydro[18]annulenes 59 a, b were prepared by oxidative Hay macrocyclization of the corresponding czs-bis(trialkylsilyl)-protected TEEs [84, 85]. X-ray crystal... 

On treatment of trialkylsilyl nitronates 1043 with MeLi, LiBr, or BuLi in THF the resulting nitrile oxide intermediates 1044 afford, in dilute THF solution (R=Me) the ketoximes 1045 in ca 50-60% yield, whereas in concentrated THF solution the O-silylated hydroxamic acids 1046 are obtained as major products [144] (Scheme 7.35). Analogously, the silyl nitronate 1047 reacts with the 2,3,4,6-tetra-O-acetyl-/ -D-glucopyranosyl thiol/triethylamine mixture to afford, via the thiohydroxi-mate 1048, in high yield, a mixture of oximes 1049 which are intermediates in the synthesis of glucosinolate [145] (Scheme 7.35). 

Two preparations of diesters of phosphonous acid have been reported, - One of these, which claims to be the first preparation of these derivatives, involves the reaction of ammonium hypophosphite with triaikylsilylamines to give bis(trialkylsilyl) esters (127) in excellent yield. These compounds are extremely reactive, e.g. they are spontaneously inflammable in air. Dialkyl phosphonites (128) have also been prepared by the reduction of... 

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