T-butylacetylene

The organometallic chemistry of alkynylcyclopropanes involves primarily the formation and reactions of carbon-metal er-bonds. Metals come essentially from the main group elements, with lithium playing a major role. The two metallation sites are the cyclopropyl and the acetylenic positions, which are expected to differ considerably in their acidity values (t-butylacetylene, pKa = 25230, cyclopropane, pKa = 46183) but less in the reactivity of their metal conjugated bases towards electrophiles. 

Suggest a mechanism for formation of the 3-methyl-l-naphthol which is consistent with the observation that similar cyclisation of the deuterated alkyne 1 gave the naphthol 2. What conclusion can be drawn from the fact that use of t-butylacetylene instead of propyne in the above sequence gives 3-t-buty 1-1 -naphthol in 75% yield for the cyclisation step ... 

Condensation of 2-pyrone with dimethyl acetylenedicarboxylate and diethylacetylene proceeds in the expected manner. There is, however, no reaction between di-t-butylacetylene and 2-pyrone, even after solutions of the reactants in bromobenzene have been heated in a sealed tube at 210°C for 5 days. Instead, frans-cinnamic acid is obtained in low yield. 

Protolysis of the bridging methyl groups in 48b with t-butylacetylene results in stepwise formation of the /t-alkynyl derivatives 49b and 50b (Scheme 6) [27]. 

It is noteworthy that alkyne dimerization may also lead to butatriene derivatives RCH=C=C=CHR. This product was first found for t-butylacetylene with... 

Addition of hydrogen chloride to t-butylacetylene has been studied in neat mixtures in the liquid phase at room temperature (3 of Table 2). Both normal and rearranged products have been isolated and the ratio of the two types of products was found to diminish by increasing the ratio HCl/t-butylacetylene. The detection of rearranged products has been explained by assuming that the initially formed vinyl cation... 

Migration to the double bond (equation 33) is a second type of interaction and is well illustrated by the nature of rearranged products obtained in the hydrogen chloride addition to t-butylacetylene (section II,A,lc) and in the solvolysis of t-butylvinyl derivatives and a-cyclopropylvinyl derivatives (section II,C,2). 

Due to activation of the furan a-positions, regioselective Sonogashira reactions can be achieved at C(2) rather than C(3) [56, 57]. For example, dibromofuran 151 reacts smoothly with t-butylacetylene to provide trisubstituted furan 152. Similar selectivity is observed for Sonogashira reactions of 2,3-dibromo and 2,3,5-tribromobenzofurans [18, 58]. 

Ethylene and thioformaldehyde are the products of irradiation of matrix-isolated thietane at lOK. Sulphur-carbon bond homolysis has also been observed on irradiation of the nucleoside membrane transport inhibitor, 6-[ (4-nitrobenzyl) thio] -9- (/8-D-ribofuranosyl) -purine (94), and the oxazolidin-2-one (95) has been converted into the allyl derivative (96) by photochemically induced radical allylation.Efficient conversion of cyclic thioacetals into the corresponding carbonyl compounds under neutral conditions has been achieved by 2,4,6-triphenylpyrylium tetrafluoroborate-sensitised irradiation in moist dichloromethane,and diaryl sulphides and the corresponding sulphoxides and sulphones have been reported to undergo anion-promoted carbon-sulphur bond photocleavageboth processes appear to involve an initial electron transfer. Sulphur-hydrogen bond horaolysis has been reported in t-butanethiol and is also responsible for the photoinitiated thiylation of fluorobromoethylenes and of trialkylethynylsilanes and t-butylacetylene. 

The jt-related II is obtained in 42% when Fe3(CO)i2 is refluxed in methylcyclohexane with di-t-butylacetylene The reactions of alkynes with tri- and tetrametallic carbonyl clusters of Fe, Ru and Os produce few ( -alkyne) products, but their formation follows a more complex pathway than the simple CO displacement, e.g., the compound Ru4(CO)i2(/- f"-RC2R) ... 

Lithium organocupmtes. House et al. have found that certain undesirable side reactions in the preparation of lithium organocuprates can be minimized by use of this complex rather than commercial cuprous bromide itself, which apparently contains some impurities. The complex is readily prepared in 90% yield from (CH3)2 S and CuBr. It is insoluble in ether, hexane, acetone, methanol, and water, but dissolves in several solvents in the presence of excess (CH3)2S. Thus a solution of the complex in ether and (CH3)2S is used the excess sulfide is readily separated from reaction products. The soluble copper reagent t-BuC CCu can also be used instead of CuBr, but the precursor, t-butylacetylene, is expensive. The use of the complex was illustrated for reactions of (CH3)2CuLi and (CH2=CH)2CuLi. 

M0CI5 and WCl6 alone can induce the polymerization of various monosubstituted acetylenes. The use of a suitable organometallic cocatalyst enhances the catalytic activity. With these catalysts, polymer molecular weight is low or medium (<10 ) for 1-hexyne and phenylacetylene but reaches one million for sterically crowded monomers like t-butylacetylene and or /2o-substituted phenylacetylenes. 

As far as the mechanism for those processes is concerned, taking into account (i) Viehe s work on t-butylacetylene (Viehe et al., 1964), (ii) the mildness of the trimerization conditions, (iii) the symmetry restrictions for the relevant conversions, (iv) the steric repulsions among perchlorotriphenyl groups and (v) the presumed electronic stability of the intermediates, it is postulated that a dimeric head-to-head diradical is formed first. This then cyclizes to give two bicyclic diradicaloid structures possessing minimal steric repulsions among the substituents (cyclobutadiene and quasi-tetrahedrane structures). By addition of a third molecule of perchlorophenylacetylene, only the 1,2,3- and the 1,2,4-isomers would result (107) (Ballester et al.. 

This catalyst system exhibits excellent functional-group tolerance cross-couplings proceed in the presence of alcohols (Table 9, entry 1), cyanides (entries 2 and 5), esters (entries 3 and 4), and ketones (entry 6). Alkyl bromides and iodides are selectively coupled in the presence of alkyl chlorides (entries 3 and 6). Finally, even very hindered alkynes are suitable cross-coupling partners (e.g., t-butylacetylene, entry 2). 

Aryne-nickel complexes, which were carefully studied by Bennett [6, 7], show a different reactivity, since following the insertion of a first unsaturated species, the metallacycles so formed usually undergo a second insertion and subsequent reductive elimination (Scheme 9). Thus, complex 44 undergoes the insertion of two molecules of 3-hexyne to afford 43 in good yield, and double insertion of the asymmetric alkyne t-butylacetylene into complex 44 yields naphthalene 45 with a high regioselectivity attributed to steric factors. Interestingly, the reaction of 44 with the more electron-deficient alkyne hexafluoro-... 

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