Butadiynes synthesis

Scheme 31. Attempted synthesis of spirocyclopropanated butadiyne-expanded [n]rotanes from the acyclic precursors 150 and 151...

Asymmetric hydrosilylation can be extended to 1,3-diynes for the synthesis of optically active allenes, which are of great importance in organic synthesis, and few synthetic methods are known for their asymmetric synthesis with chiral catalysts. Catalytic asymmetric hydrosilylation of butadiynes provides a possible way to optically allenes, though the selectivity and scope of this reaction are relatively low. A chiral rhodium complex coordinated with (2S,4S)-PPM turned out to be the best catalyst for the asymmetric hydrosilylation of butadiyne to give an allene of 22% ee (Scheme 3-20) [59]. 

In a semimicro synthesis selenophene is prepared from bis(trimethylsilyl)-1,3-butadiyn and NaHSe generated in situ from Se and NaBH4 in aqueous dimethylformamide.52 Other ring cyclization reactions have been performed... 

N-Bromoiraides, 46, 88 />-Bromophenyl isothiocyanate, 46, 21 Butadiene, 46, 106 Butadiyne, diphenyl, 46, 39 A -Butenolide, 46, 22 i-Butyl alcohol in synthesis of phenyl 1-butyl ether, 46, 89 1-Butyl azidoacetate, 46, 47 hydrogenation of, 46, 47 1-Butyl chloroacetate, reaction with sodium azide, 45, 47 i-Butyl hypochlorite, reaction with cy-clohexylamine, 46,17 1-Butylthiourea, 46, 72 1-Butylurea, 46, 72... 

Thiols very readily add to diacetylene in the presence of bases, such as alkoxides, with formation of enyne sulfides HC=CCH=CHSR [175]. In strongly basic media, thiol can be eliminated from these enyne derivatives [2], Thus, functionalization of HChCCH=CHSR followed by treatment with an excess of sodium amide results in a derivative of butadiyne. This sequence of conversions permits the synthesis of some 1,3-diyne systems that are not otherwise easily accessible. 

Oxidative coupling of terminal acetylenes in the presence of copper(I) catalysts is the best method of preparing symmetrically substituted butadiyne derivatives,5 and has been applied to the coupling of trimethylsilyl-acetylene. Better yields are obtained using the Hay procedure in which the catalyst is the TMEDA complex of copper(I) chloride.7 The procedure submitted here is an improved version of Walton and Waugh s synthesis of BTMSBD by the Hay coupling of trimethylsilylacetylene.2 BTMSBD has also been prepared by... 

Bauerle and coworkers have adapted the Cu+ template (48) approach to [2]cate-nane synthesis using an intermediate platinum diacetylide linkage to macrocyclize each of the two rings (49, Scheme 10.9) [38], Oxidation of the platinum centers in the macrocyclic rings of SO with I2 induces reductive elimination of the two acetylides to form the 1,3-butadiyne linked macrocycles (51). Unfortunately, the authors could not remove the copper template in this example, likely as a result of steric congestion about the metal ion in the interlocked product. 

Fig. 16.33. Pd(0)-catalyzed alkynylation of a copper acetylide with a silylated ethynyl iodide in a two-step synthesis of a monosilylated 1,3-butadiyne. If the same copper acetylide is alkynylated with higher alkynyl iodides and subsequently heated with potassium carbonate in toluene, monoalkylated 1,3-butadiynes result - The Pd-free alkynylation of a copper acetylide ("Cadiot-Chodkiewicz coupling") is shown in Figure 16.9.

A highly chemo- and regioselective [2 + 2 + 2] sequential cycloaddition of alkynes and 1,3-butadiynes catalyzed by Pd(0) complexes as an elegant de novo synthesis of tetrasubstituted benzenes 216 (Scheme 88) and pen-... 

The reaction has found limited use for the direct synthesis of terminal polyacetylenes, as illustrated by the formation of phenylhexatriyne (70%) from butadiyne and bromophenylacetylene (equation 12) . The concomitant formation of diphenyl-octatetrayne (30%) in this reaction illustrates the major drawback to this route, i.e. further coupling of the initial product. 

SCHEME 18.12 Synthesis of silylene acetylene ( polyalkynylsilanes , left and right) or diacetylene polymers ( polybutadiynylsilanes , middle) by metathesis of dichlorosilanes and dilithium reagents of acetylene, silylenediacetylene and butadiyne, respectively. ... 

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