Diynes arenes

A subsidiary approach involves nuclear modification of the arylsilanes so obtained. The requisite organometallics can be prepared from aryl halides, or by deprotonation of a suitably activated (c.g. methoxy-substituted) arene. A more specialized route involves cycloaddition between alkynylsilanes and diynes. 

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

The methodology is useful for a variety of synthetic purposes. The cycloadditions are not subject to steric hindrance. Thus diyne cycloadditions to 2,5-disubstituted furans or pyrroles, followed by elimination of the oxygen or nitrogen bridges, provides an excellent, short route to peri-substituted arenes, as in the following examples 4 6 8... 

Reductive Cyclization of 1,6- and 1,7-Dienes, Diynes, Enynes and Arenes via Zirconacycles and Titanacycles... 

A two-step synthesis of arenediynes from arene-1,2-dialdehydes has been reported (Scheme 15). Dibromomethylenation of dialdehydes under Corey-Fuchs conditions provides the tetrabromides, which on treatment with n-BuLi or LDA afford 3,4-unsaturated 1,5-diynes, the key structural moiety present in several naturally occurring... 

In a similar vein, cyclizations of diynes bearing propargyl carboxylates have been described to synthesize dienes and pyrones (equation 90). In the last case, a new cascade allows the intermolecular addition of electron-rich arenes. ... 

Arenes from enynes and diynes. A novel synthesis of alkynylarenes by the intermolecular cycloaddition of enynes and diynes has been developed. With enynes alone the products are 2,6-disubstituted styrenes which are formed by cyclodimerization. Note that benzynes undergo trimerization to give triphenylenes in situ, e.g., by treatment of o-trimethylsilylphenyl triflate with CsF in the presence of (PhjPl.Pd. ... 

Transition metal catalysts can also be used in photochemical organic synthesis. For example, the photo-Bergman reaction (cycloaromatization see also Scheme 6.62) of (Z)-hex-3-en-l,5-diyne [(Z)-589], which is obtained by photostationary E Z isomerization (Section 6.1.1) from ( )-589, occurs via transition metal-catalysed cycloaromatization reaction followed by photochemical dissociation of the arene ligand from the complex 590 (Scheme 6.289).1530 The product, 1,2-di( -propyl)benzene (591), is obtained in 91% chemical yield. 

Thermal reaction of two alkyne groups forms the basis of the Bergmann rearrangement, in which l,5-diyne-3-enes form arene-l,4-diyls (69). The reaction rate is influenced by the radical trapping agent used ". ... 

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