Fused arenes

A palladium-mediated Stille-C-H functionalization process was recently disclosed. Deuteration of the fused arene led to 92% D-incorporation in the vinylsilane product, suggesting a Pd-migration process (Equation (159)).133... 

The principal methods for the construction of 1,2,5-oxadiazole frameworks were already well developed in 1984 when CHEC-I was published, and this section is therefore designed to update this coverage. Different approaches are generally required for furazans and furoxans, and furthermore the methods used for 3,4-fused arene analogues are also quite distinct. Separate sections are thus devoted to furazans, benzofurazans, furoxans, and benzofuroxans unless otherwise stated the material included is cited in the reviews listed in the Introduction to this chapter. 

Apart from the construction of phenanthrenes, carbene complexes have also been used for the synthesis of more extended polycyclic arenes. An unusual dimerization of chromium coordinated ortbo-ethynyl aryl carbenes results in the formation of chrysenes (Scheme 37) [81]. This unusual reaction course is presumably due to the rigid C2 bridge that links the carbene and alkyne moieties, and thus prevents a subsequent intramolecular alkyne insertion into the metal-carbene bond. Instead, a double intermolecular alkyne insertion favored by the weak chromium-alkyne bond is believed to occur forming a central ten-membered ring that may then rearrange to the fused arene system. For example, under typical benzannulation conditions, carbene complex 97 affords an equimolar mixture of chrysene 98a and its monochromium complex 98b. The peri-interactions between the former alkyne substituent (in the 5- and 11-positions) and the aryl hydrogen induce helicity in the chrysene skeleton. 

This type of -coordination is often encountered for complexes of naphthalene An + 2= IOtc), where some aromaticity An + 2 = 6tc) is retained in the second ring of the fused arene. The drive towards buta-1,3-diene coordination may be sufficient to favour rearrangement of non-conju-gated dienes, or the ring opening of cyclopropylalkenes (Figures 6.2, 6.6,... 

Halide ions, multiple valence metal ions (transition metal complexes), viologen, triarylamines, nitroxyl radicals, and fused arenes like naphthalene are used as mediators for this method. Mediators very often act as an electrocatalyst. 

The intramolecular hydroarylation of alkynes is a useful method for the synthesis of fused arenes. For example, biphenyl derivatives, bearing an alkyne unit at the ortho position, were converted into substituted phenanthrene derivatives in the presence of various jc-electrophihc transition metal catalysts such as platinum, palladium, gold, gaUium, indium, iron, and so on (Scheme 21.48) [54]. 

General Remarks About the Fused-Arene Complexes and ... 

SYNTHESIS OF RARE EARTH FUSED-ARENE COMPLEXES AND THEIR REACTIVITY TOWARD P4 ACTIVATION... 

Scandium Fused-Arene Complexes Synthesis, Characterization, and Reactivity... 

The catalytic protocol can also be applied to the reductive cleavage of pivaloxy groups on arenes, fused arenes, and heteroarenes [Eq. (11)] [59]. 

S-Containing Polycyclic Heteroarenes Thiophene-Fused and Thiadiazole-Fused Arenes as Organic Semiconductors... 

As described in this chapter, a large number of novel thiophene- and thiadiazole-fused arenes have been developed for their apphcation in OFETs. Their device performances have remarkably improved in recent years, with mobilities >1.0cm s having occasionally been achieved. Representative organic... 

These cycloaddition conditions were amenable to various diynes (Scheme 2.5). Alkynes such as phenylacetylene, benzyl-protected propargyl alcohol, and a Boc-protected propargyl amine were ail coupled effectively with malonate and N -backbone terminal diynes (21 to 23). Activated diynes also show excellent reactivity with internal and terminal alkynes. Notably 6,6-fused arenes can also be accessed in fair yields (25) using this protocol. The yield drops slightly when an internal alkyne (26) is employed. 

Fig. 33 Conformation of benzo-fused bicyclo[4.4.1]undecanone and ketal. (a) Pseudo boat/boat, boat/chair and chair/chair conformations of bicyclo[4.4.1]undecanone (b) ketaUzation or addition of Grignard reagent locks bicyclic framework into pseudochair/chair conformation in which the fused arenes are stacked atop one another (c) structural parameters for pseudo chair-chair conformation of benzo-fused bicyclo[4.4.1]undecanone core...

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