Bis trimethylsilyl acetylene

Dipolar cycloaddition reaction of trimethylstannylacetylene with nitrile oxides yielded 3-substituted 5-(trimethylstannyl)isoxazoles 221. Similar reactions of (trimethylstannyl)phenylacetylene, l-(trimethylstannyl)-l-hexyne, and bis (trimethylsilyl)acetylene give the corresponding 3,5-disubstituted 4-(trimethyl-stannyl)isoxazoles 222, almost regioselectively (379). The 1,3-dipolar cycloaddition reaction of bis(tributylstannyl)acetylene with acetonitrile oxide, followed by treatment with aqueous ammonia in ethanol in a sealed tube, gives 3-methyl-4-(tributylstannyl)isoxazole 223. The palladium catalyzed cross coupling reaction of... 

The zirconacyclopropene 1, which was prepared by treatment of Cp2ZrCl2 with magnesium metal in the presence of bis(trimethylsilyl)acetylene, reacted with one molecule of C02 under atmospheric pressure at room temperature to give the dimeric zirconacycle 2 in good yield (Scheme iy6>6a>6b Further insertion of C02 did not occur, although 2 has... 

Organometallic Chemistry of Titanocene and Zirconocene Complexes with Bis(trimethylsilyl)acetylene as the Basis for Applications in Organic Synthesis... 

Novel Titanocene and Zirconocene Reagents with Bis(trimethylsilyl)acetylene... 

Figure 10.1. Novel titanocene and zirconocene reagents incorporating bis(trimethylsilyl)acetylene.

Scheme 10.1. Co-reactions of the bis(trimethylsilyl)acetylene (A) or reactions of the substrate (B) at the metallocene as the basis for an associative or dissociative mechanism.

Internal RC=CR Symmetrically disubstituted acetylenes such as tolane PhC=CPh react with complex 1 by substitution of the bis(trimethylsilyl)acetylene with formation of the metallacydopentadiene 7 [2a,2d],... 

Using the unsymmetrically substituted acetylene Me3SiC=CPh, the kinetically favored substituted complex 8a is formed initially, cycloreversion of which gives the symmetrically substituted and thermodynamically more stable product 8b. Due to steric reasons, the other conceivable symmetric product 8c is not formed [9]. Such metallacycles are typically very stable compounds and are frequently used in organic synthesis, as shown by the detailed investigations of Negishi and Takahashi [lm], Bis(trimethylsilyl)acetylene complexes are a new and synthetically useful alternative. 

No defined complexes could be isolated from reactions of complex 1 with acetone Me2C=0. Complexes 2a and 2b react with acetone to give the zirconafuranone 2c, which is an interesting zirconocene precursor in view of its extremely good solubility in hydrocarbon solvents and because of its ability to dissociate into the alkyne complex [2f], It is also possible to cleanly substitute the bis(trimethylsilyl)acetylene unit so as to obtain the complex 47, or, alternatively, to substitute the acetone with formation of the zirconafuranone 95 (Fig. 10.14) [2f],... 

Complex 1 reacts with benzaldehyde with elimination of bis(trimethylsilyl)acetylene to produce the titanadioxacydopentane 57 [39]. With benzophenone or formaldehyde, no products are isolated [35]. 

The reactions of complex 2a with ketones and aldehydes show a strong dependence on the substituents. With benzophenone, substitution of the silyl-substituted acetylene leads to the r]2-complex 58, which is additionally stabilized by a THF ligand. This complex can serve as an interesting starting material for other reactions. With benzaldehyde and acetophenone, the typical zirconadihydrofuran 59, akin to 2c, is obtained from a coupling reaction. This complex is unstable in the case of benzaldehyde and dimerizes, after elimination of bis(trimethylsilyl)acetylene, to yield 60. In this respect, it is similar to the above discussed complex 2c, since both of them show a tendency to eliminate the bis(trimethyl-silyl)acetylene. The reaction of methacrolein with complex 2a depends strongly on the solvent used [40]. 

In THF, insertion into 2a with the formation of complex 61 is found, whereas in n-hexane, elimination of the bis(trimethylsilyl)acetylene leads to the formation of 62. 

The side products of the reactions, e. g. bis(trimethylsilyl)acetylene, THF, pyridine, acetone, etc., are soluble and volatile and are thus easy to remove. 

Scheme 10.9. Synthesis of titanocene (1, 3, rac-5) and zirconocene (4, rac-6) complexes with bis(trimethylsilyl)acetylene without additional ligands.

Scheme 10.10. Synthesis of zirconocene complexes (2a and 2b) with bis(trimethylsilyl)acetylene containing additional ligands following the routes used by Rosenthal and Tilley.

Sonogashira reactions of both a-halothiophenes [117] and P-halothiophenes [118] proceed smoothly even for fairly complicated molecules as illustrated by the transformation of brotizolam (134) to alkyne 135 [119]. Interestingly, 3,4-bis(trimethylsilyl)thiophene (137), derived from the intermolecular cyclization of 4-phenylthiazole (136) and bis(trimethylsilyl)acetylene, underwent consecutive iodination and Sonogashira reaction to make 3,4-bisalkynylthiophenes [120], Therefore, a regiospecific mono-i/wo-iodination of 137 gave iodothiophene 138, which was coupled with phenylacetylene to afford alkynylthiophene 139. A second iodination and a Sonogashira reaction then provided the unsymmetrically substituted 3,4-bisalkynylthiophene 140. 

The unexpected formation of the first bis(triorganosilyl)silyl dianions has been reported by Sekiguchi et al. in 1999. Thus, the reaction of l,l-bis(triorganosilyl)-2,3-bis(trimethylsilyl)silacyclopropenes 128 and 129 with lithium provided the dilithiosilanes Li2[Si(R2R Si)2] (130 R = R1 =/-Pr 131, R = Me, R1 =/-Bu) with the only byproduct being bis(trimethylsilyl) acetylene Me3SiCCSiMe3 132 (Scheme 21 ).281>282 For reactions of silyl dianions at preparing unsaturated silanes, see Section 5.2. 

A series of novel ruthenium(IV) dioxolene complexes, formally [3 + 2] cycloadducts, have been obtained via the reaction of cix-[Ru (0)2(Me3tacn)(CF3C02)] with trimethylsilylacetylenes (Scheme 14). " These dark blue complexes display a characteristic UV-vis absorption band at 550-680 nm. They are also characterized by electrospray mass spectrometry. The X-ray structure of the complex formed with bis(trimethylsilyl)acetylene has been determined the two Ru—O bonds of the metallocycle are of the same length (1.978 A). 

Unlike zirconium, the group IV metal titanium does not form the hydrometalation product but rather a (r -C5Q)-complex. The first titanium-fullerene complex 1 was prepared by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene with equimolar amounts of Cjq (Scheme 7.1). 

Recently, a new approach to 3,4-disubstituted thiophenes via the 3,4-disilylated thiophene 108 was reported (160). The synthesis includes the cycloaddition of la to bis(trimethylsilyl)acetylene and subsequent dehydration of cycloadduct 107 with DDQ to give 108 (Scheme 5.39). The trimethylsilyl groups can be substituted in a stepwise manner to give unsymmetrical 3,4-disubstituted thiophenes (109). 

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