Cycloadditions trimethylsilylacetylene

Norbornadienes, norbornenones and their homologs have been prepared [23, 24] by cycloaddition of cyclopentadiene (21) and cyclohexadiene (22) with l-benzenesulfonyl-2-trimethylsilylacetylene (23) and l-ethoxy-2-carbomethox-yacetylene (24). Both were efficient dienophiles in the cycloaddition processes and dienophile 23 acted as an effective acetylene equivalent (Scheme 2.12). Norbornanes and their homologs can also be attained by Diels-Alder reaction... 

Facile addition of either alcohols or amines to carbene complex 288 produces the / -am i n o-a, /i-unsaturated carbene complexes 289, which are useful for the preparation of cyclopentenone derivatives. Insertion of alkyne to 289 gives the 1,3-dienylcarbene complex 290, and its formal [3+2] cycloaddition gives cyclopentadiene 291. Under different conditions, [2+2+1] cycloaddition of vinylketene 292 produces the 5-methylene-2-cyclopentenone derivative 293 [88], The cyclopentenone 295, isomeric to 293, was obtained by the reaction of complex 294 with trimethylsilylacetylene, and oudenone (296) was synthesized by its hydrolysis [89]. 

The Homo Diels-Alder Reaction of Norbomadiene with Acetylenes. [2 + 2+2] Cycloadditions of dienes such as norbomadiene with the double bonds in 1,4-position are called homo Diels-Alder reactions. Using an in situ catalyst (consisting of Co(acac)3-Et2AlCl-bis(diphenylphosphino)ethane) the products obtained with monosubstituted acetylenes, such as phenyl, i-propyl-, n-butyl-, t-butyl-, and trimethylsilylacetylene, are 4-substituted deltacyclenes. - In the formation of the polycyclic deltacyclene skeleton, six new stereo centers are generated in one step. Thus enantiocontrol by using optically active phosphine ligands as cocatalysts allows the synthesis of optically active cycloadducts, as shown for the reaction of norbomadiene with phenylacetylene to give 4-phenyldeltacyclene (eq 1). 

Preparation of Heterocycles. BSA has been used in the solid-phase synthesis of 1,2,3-triazoles via trimethylsilyl-directed 1,3-dipolar cycloaddition reactions of 1-trimethylsilylacetylenes with organic azides (eq 48). When resin 56 was allowed to react with trimethylsilylpropynoic acid in the presence of BSA, high regioselectivity was observed and the trisubstituted triazole 57a was obtained in near quantitative yield that is greater than 98% purity. 

Schubert et al. subjected to a systematical examination reactions of l,3-[3 h-21-cycloaddition of substituted aromatic azides to trimethylsilylacetylenes in water affording regioisomeric 1,2,3-triazoles, in particular, those containing a perfluoroaryl substituent at endocyclic atoms of the heterocycle 125,126 [111]. 

Tethered yne-enamides can also participate in cobalt-mediated crossed [2 -t- 2 -t- 2] cycloadditions with bis-trimethylsilylacetylene, and such a strategy was exploited in synthetic approaches to the lycorane skeleton [57]. Even more, the cobalt-mediated [2 -I- 2 -I- 2] cycloaddition reaction can be extended to use of the heteroaromatic double bond in benzofiiranes and indoles. The former was used to gain access to morphinoids [58], whereas the latter emerged into a short synthesis of (+)-strychnme (190) (Scheme 7.41) [59]. 

In an analogy to the well-known octacarbonyldicobalt-mediated Pauson-Khand reaction, the formal [2+2+1] cycloaddition of alkyne, alkene, and carbon monoxide can be promoted by pentacarbonyliron. However, the iron-mediated [2+2+1] cycloaddition of two alkynes with carbon monoxide has attracted much more attention. When heated in glyme at 140 °C in the presence of stoichiometric amounts of penta-carbonyliron, substituted trimethylsilylacetylenes afford tricarbonyliron complexed cyclopentadienones in moderate to good yields (Scheme 4-3). ... 

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