Butatriene derivatives

The cyclodimerization of 82 to 83 is an example of a Ni(0)-mediated synthesis of [4]radialenes from [n]cumulenes. Applications of this method to butatriene derivatives 9050,63, 9164 and 9365,66 are shown in Scheme 10. The usefulness of Ni(0) catalysis for this transformation was first demonstrated by West and coworkers63 and later explored in detail by Iyoda and coworkers42,54,67. In some cases, Ni(0) catalysis improves the... 

The dimerization of alkynes is a useful method for forming compounds such as enynes from simple alkynes [13]. The iridium-catalyzed dimerizahon of 1-alkyries was first reported by Crabtree, and afforded (Zj-head-to-head enynes using [Ir(biph)(PMe3)Cl] (biph = biphenyl-2,2 -diyl) as a catalyst [14]. Thereafter, an iridium complex generated in situ from [Ir(cod)Cl]2 and a phosphine ligand catalyzed the dimerizahon of 1-alkynes 1 to give (Tj-head-to-head enyne 2, fZj-head-to-head enyne 3, or 1,2,3-butatriene derivatives 4 in the presence of hiethylamine... 

Scheme 9.10 lr(l)-catalyzed alkyne dimerization leading to butatriene derivatives. 

The head-to-head dimerization with formation of a butatriene derivative was very scarcely observed as the main catalytic route (Scheme 10.19, cycle B). Nevertheless, this was the case with benzylacetylene in the presence of RUH3CP (PCy3) as catalyst precursor in tetrahydrofuran at 80°C which gave more than 95% of (Z)-l,4-diben-zylbutatriene [66], and with terf-butylacetylene with two efficient catalytic systems capable ofgenerating zero-valent ruthenium species, RuH2(PPh3)3(CO) and Ru(cod) (cot) in the presence of an excess of triisopropylphosphine, which led to (Z)-l,4-di-tert-butylbutatriene as the major compound [71-73]. 

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... 

Then transmetaUation to copper occurs with the formation of the monocopper butatriene derivative 321 that transformed by a second transmetaUation to the corresponding bismetaUated species 323. The latter intermediate undergoes, through an intramolecular carbometallation event, a skeletal reorganization to form the... 

Diehlorocarbene adds to the butatriene derivative 11 under phase-transfer conditions to give the [2-1-1] cycloadduct 12, which rearranges in the presence of water to give the unsaturated alcohol 13. ... 

Irradiation of a benzene solution containing l-diarylvinylidene-2,2,3,3-tetramethylcyclopropanes (7a-d) efficiently afforded l,l-diaryl-4,5,5-tetramethyl-l,2,3-hexatrienes (8a-d) in high yields. The quantum yields for the formation of 8a-d were not high (4> =0.01 0.02) as shown in Table 31.3. The photorearrangement of 2,2,3-trimethyl and 2,2-and 2,3-dimethyl derivatives 7e-f, 2a also took place, but the rates for the formation of the 1,2,3-butatrienes were quite slow and products were not isolated. The bicyclic vinyhdenecyclopropanes 7g-h also rearranged to the 1,2,3-butatriene derivatives 8e-. The structure of 8b is confirmed by x-ray crystallography. 

As indicated in the general scheme below, butatrienes are the first products from base-induced 1,4-elinination of hydrogen and a suitable leaving group. The butatriene in general very readily undergoes isomerization into enynes, if sufficiently "acidic" protons are available (see Chapter 11 in Ref. 3a). In aprotic media cumulenic ethers are fixed as their lithio derivatives if an excess of alkyllithium is applied... 

The most recent strategy to prepare [3]radialenes is the treatment of 1,1-dihaloalkenes with activated nickel. Thus, the aryl-substituted [3]radialenes (Z,E,E)-30 and (E,E,E) 30, 27 and 32 were obtained together with the corresponding butatrienes (29, 28, 31) from the 1,1-dibromo- or 1,1-dichloroalkenes with the help of nickel activated by ultrasound (Scheme 4)11. It is worth mentioning that the mixed-substituted radialene 33 was produced, when the nickel carbenoid derived from 9-(dichloromethylene)xanthene was generated in the presence of butatriene 2811. 

Radialenes represent the biggest and best known subset of the radialene family this is not surprising in view of the fact that more methods to prepare them exist than for any other class of radialenes. The major strategies are the transformation of appropriate cyclobutane derivatives, the thermal or Ni(0)-catalyzed cyclodimerization of butatrienes or higher cumulenes and the cyclotetramerization of (l-bromo-l-alkenyl)cuprates. 

Less common addition reactions such as the bromination of trifhioromethyl-substi-tuted butatrienes [30] or the reaction of tetrafluoroallene with boron trifluoride have also been reported [283]. Especially the interaction of phosphorylated allenes with electrophiles was summarized in a review by Alabugin and Brel [8], whereas Smadja [284] published a more general overview about the electrophilic addition to allenic derivatives. 

For R = H and Me, the derived values are [321.3 ( >1.9)] and [323.3 ( >1.4)] klmoF , respectively. A value of [326 ( > 4)] kJmoF for AHf(g, 1,2,3-butatriene) is thus credible. What is found for the cyclopropanation enthalpies of butatriene There are seemingly no relevant data for either of its monocyclopropanation products, dimethylenecyclopropane (25a) or vinylidenecyclopropane (25b). The two dicyclopropanation products have comparable enthalpies of formation dicyclopropylidene (26), 286.6 (1) and 324.3 (g), and meth-ylenespiropentane (27), 287.0 (1) and 320.9 (g), respectively". The 2-6 kJ moF decrease in enthalpies of formation for gaseous dicyclopropanated products is not particularly in accord with the 3 kJ moF increase per alkyl substituent of cyclopropanation of simple olefins. However, in that the allene —> methylenecyclopropane —> spiropentane (3 23 7) enthalpy of formation changes are still enigmatic, and error bars are absent for the dicyclopropanated products, we do not fret. But we eagerly await more thermochemical data. 

This is especially true for the 1,4-dilithiobutatriene derivative 133 which turns out to have a dimeric cw-structure with two different kinds of lithium atoms and a true butatriene geometry 133a (see Sect. 2.7)... 

What about the reaction enthalpy in the C4 case While there are no measured enthalpies of formation for the product butatriene, this quantity may be simply estimated. The enthalpy of formation of its 1,4-dimethyl derivative (for both the CIS- and rrans-isomers) has been determined by hydrogenation calorimetry [56] to be ca. 265 kJ mor. Demethylation of propene, 1,2-butadiene, ( )-2-butene,... 

Conversion of thiophene 2-carbaldehyde to the dibromovinyl derivative (474) can be accomplished by CBr4 and Ph3P. On metalation with Bu"Li at — 78°C, followed by quenching with water, this is converted to 2-thienylacetylene <82JOC220i, 86H(24)365>. A side reaction in this is the metalation at position 5 of the thiophene. Tetra(2-thienyl)butatriene and some of its derivatives... 

The 1-allylcycloalkanols (66 n = 0, 1, or 2 R = H) are cyclopropanated to (67 R = H) by dichlorocarbene. Yields are higher using ethyl trichloroacetate and sodium methoxide in hexane than with chloroform-potassium t-butoxide as the carbene source, but the former method gave slightly lower yields on reaction with the trimethyl-silyl derivatives of the alcohols (66 R = SiMe,). This was suggested to beastericeffect and such effects are also seen in the addition of dichlorocarbene to allenes and butatrienes. ... 

In allenes, the double bonds share a central carbon atom. There are other cumulated molecules in which heteroatoms (noncarbon atoms such as oxygen or nitrogen) take the place of one or more carbons of an allene and/or in which there are more than two double bonds in a row. When one end carbon of allene is replaced with an oxygen, the compound is called ketene (Fig. 12.6). If both end atoms are oxygens, the molecule is carbon dioxide. Cumulated hydrocarbons with three double bonds attached in a row are called cumulenes, although they can also be named as derivatives of 1,2,3-butatrienes (Fig. 12.6). Cumulenes are very reactive and most difficult to handle. 

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