1.3- butadiynes

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],... 

It seems quite obvious that the thiophenes are related to the polyacetylenes which they accompany. This viewpoint has recently been illustrated by the formation of thiophenes from polyacetylenes and hydrogen sulfide under almost biological conditions. In a recent lecture summary, the preparation of terthienyl, junipal, and (241) from 1,4-disubstituted butadiynes and hydrogen sulfide is claimed. A large number of bithienyls have been prepared and their nemato-dicidal activity investigated. All the compounds with strong activity were found to be derivatives of 2,2 -bithienyl. ... 

The composition of the mixture of products of different structures depends on the diacetylene diazomethane ratio (68LA124). With a 1 1 ratio of butadiyne and diazomethane, 3(5)-ethynylpyrazole dominates (55%). The yields of isomeric 3- and 5-ethynyl-l-methylpyrazoles are 8 and 11%, respectively. The double excess of diazomethane leads mainly to a mixture of N-methylated isomers (81%), 10% of 3(5)-ethynylpyrazole, and a small amount (3%) of bipyrazole (68LA124) (Scheme 3). 

Thus, 1,4-dibenzoyl- 1,3-butadiyne with diazomethane forms 3(5)-benzoylethy-nylpyrazole (yield 59%) (68LA124). In a similar way, the reaction of 2,7-dimethyl-octadiyne-2,7-diol with diazomethane leads to 4-[3-(l-hydroxy-l-methylethyl)-l//-pyrazol-4-yl]-2-methylbut-3-yn-2-ol in 64% yield (58CB1841) (Scheme 7). 

Note that 1,4-substituted butadiynes with diazomethane can form two isomers. Kuznetsov and co-workers have considered this problem in detail and established that diphenyldiacetylene with diazomethane forms, in standard conditions (ether, 0°C, 9 days), only one of the two possible regioisomers 4-phenyl-3(5)-phenylethynylpyrazole (yield 86%) (93ZOB1107). The cyclization of derivatives of phenoxy-2,4-hexadiyn-6-oles with diazomethane leads to only one isomer of alkynylpyrazole (76MI1 77MI1) (Scheme 8). 

Similarly, the cross-coupling of N-protected 4-ethynylpyrazole with 1-(1-ethoxyethyl)-4-iodo- l//-pyrazole leads only to disubstituted butadiyne (2001 UP 1) (Scheme 50). 

It was found [99JCS(PI )3713] that, in all cases, the formation of the deiodinated products 38 and 39 was accompanied by formation of the diynes 40 which were isolated in 60-90% yield. The authors believed that the mechanism of deiodination may be represented as an interaction ofbis(triphenylphosphine)phenylethynyl-palladium(II) hydride with the 4-iodopyrazole, giving rise to the bisftriphenylphos-phine)phenylethynyl palladium(II) iodide complex which, due to the reductive elimination of 1 -iodoalkyne and subsequent addition of alk-1 -yne, converts into the initial palladium complex. Furthermore, the interaction of 1-iodoalkynes with the initial alkyne in the presence of Cul and EtsN (the Cadiot-Chodkiewicz reaction) results in the formation of the observed disubstituted butadiynes 40 (Scheme 51). 

The presence of the aliphatic amino group complicates the course of the reaction. Thus, the oxidative coupling of 4-ethynyl-1,3-dimethyl-5-aminomethylpyrazole in mild conditions (20°C, CuCl, pyridine, O2) leads to only 20% of butadiyne. However, acylic protection eliminates these complications, and 4-ethynyl-1,3-dimethyl-5-(acetyl)aminomethylpyrazole forms a dehydrodimer in 95% yield (Scheme 66) (86TH1). 

Would you expect a conjugated diyne such as 1,3-butadiyne to undergo Diels-Alder reaction with a dienophile Explain. 

Tieke, B. Polymerization of Butadiene and Butadiyne (Diacetylene) Derivatives in Layer Structures. Vol. 71, pp. 79 — 152. 

In contrast, the trimer 89 with ethyne and butadiyne links stabilizes the thermodynamically disfavored endo transition state, and the endo adduct 86 is rapidly and almost exclusively formed. 

Acetylene-Expanded [n]Perkyclmes and Butadiyne-Expanded [n]Rotanes... 

Synthetic Routes to Expanded [nlPericyclines and Butadiyne-Expanded [nJRotanes... 

Scheme 17. The main building blocks for butadiyne-expanded [n]rotanes and their per-methylated analogues...

When the acyclic dehydrohexamer 156 was oxidatively cyclized, an increased yield (49%) of the butadiyne-expanded [6]rotane 166 was observed, but the yield of the expanded [12]rotane 171 with a Cgo inner ring suffered from the fact that the corresponding acyclic dehydrododecamer 159 slowly decomposed in the syringe pump [48]. 

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

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