Tetracyclone,

The stability of the o-bromothienyllithium reagents at —70°C contrasts sharply with the behavior of o-bromophenyllithium which is very unstable even at — 100°C, readily splitting off lithium bromide to form benzyne (dehydrobenzene).Only by heating bis-(3-iodo-2-thienyl)mercury to 240°C in the presence of tetracyclone could some evidence for the intermediate existence of 2,3-dehydrothiophene be obtained. ... 

Section II, A, 3)], by conversion into the mercury compound 102 and subsequent heating. Aryne 98 was trapped with tetracyclone and the product (103) was formed in 70% yield. 

In the context of this section it is important that Ruchardt and Tan (1970 a) found that (solid) benzenediazonium fluoroborate gave benzyne adducts with potassium acetate in the presence of aryne trapping agents such as tetracyclone or anthracene. This is, however, not the case if water is present (Cadogan, 1971). As a consequence of these observations, Cadogan et al. (1971) simplified the formation of arynes from diazonium ions by converting aniline or its substitution products into arynes in a... 

D. Miscellaneous.—A further study of the reactions of diphenyl-phosphine oxide with tetracyclone has confirmed that the reaction yields the oxide (30) under mild, basic conditions, and that the reaction is thermally reversible. The displacement of halogen from phosphorus by amino-compounds has been used in the synthesis of a number of aminofluoro-phosphine oxides (31), and of A-methyl-AA-bis(dichlorophosphinyl)-amine (32). ... 

The reaction of tetraphenylcyclopentadienone (tetracyclone) with dialkyl phosphites has invoked further interest. Miller has shown that reactions at 20 °C in the presence of sodium bicarbonate lead to products (35) and (36), with phosphorus substituted at carbon rather than oxygen. Quite different products (37) and (38) are obtained at 160 °C, although whether (38) is obtained from initial attack at oxygen or carbon is still unresolved. 

Dimethyl anthracene and diphenyl isobenzofuran form remarkably stable233 cyclopropanone derivatives (353/354), whilst with other diene components (butadiene, tetracyclone, and fulvene) the primarily formed Diels-Alder adducts either suffer ketalizing attack of the solvent (356 - 357, 359 - 358/360) or undergo irreversible changes such as decarbonylation to 362 or rearrangement to 355. 

Ru3(CO)10(Ph2C2)2, and Ru3(CO)9(C2(Ph)2)3 (128). The dinuclear complex Ru2(CO)6(C2Ph2)2, containing a metallocyclopentadiene ring similar to that observed for both iron and osmium, is a further product in the reaction this does imply very similar structures for the trinuclear adducts to those observed for iron and osmium. The carbonyl reacts with tetracyclone to yield the complex Ru3(CO)i0(C2Ph2)2, which may be related to the osmium compounds discussed later. Phosphine substitution of the carbonyls in some of these compounds has been established. 

In order to confirm the existence of the strained cyclophyne 77, Chan also generated 77 by an emphatic route, using the 1,2,3-selenadiazole 83 as a starting material. Thus, pyrolysis of 83 at 220 °C in the presence of tetraphenylcyclopen-tadienone (tetracyclone) gave 84, after extrusion of CO. The existence of cyclophyne 77 as an intermediate seemed evident (Scheme 18). 

Diazene, furan ozonide decomposition, 730 Diazo compounds, ozone adducts, 734 Diazonium salts, TEARS assay, 667 Dibenzoyl peroxide, determination, 698 Z-Dibenzoylstilbene, tetracyclone bleaching, 734-5... 

Tetracyanoethylene complexes, disilanes, 816 Tetracyclone, bleaching, 734-5 Tetraethylammonium ozonide, 736 Tetragermabuta-1,3-diene, 825, 826 Tetrahedral distortion acychc organic peroxides, 103 alkyl hydroperoxides, 110 anion ligands, 119... 

Some unusual syntheses of substituted 2,2 -bipyridines deserve mention. Tetracyclone (tetraphenylcyclopentadienone) on heating with picolinonitrile at 215°C affords 3,4,5,6-tetraphenyl-2,2 -bipyridine, whereas 5-methyl-2,2 -bipyridine and some polysubstituted 2,2 -bipyridines are obtained by the oxidative degradation of the antibiotic streptonigrin. 5-Aldehydo-6-amino-2,2 -bipyridines are obtained by acid hydrolysis of pyrido[2,3-[Pg.311]

A number of syntheses of substituted 2,3 -bipyridines are worthy of note. Tetracyclone heated at 215°C with nicotinonitrile affords 3,4,5,6-tetraphenyl-2,3 -bipyridine, whereas 3,4-di(2-pyridyl)pyridine is obtained by an oxidative degradation of the corresponding 6,7-disubstituted thiazolo[3,2-a]-pyridinium salt. Nicotinic acid on UV irradiation in aqueous solution at pH 4-6 gives 2,3 -bipyridine-5-carboxylic acid, whereas irradiation of picolinic acid in the same pH range in the absence of metal ions gives some 2,3 -bipyridine. 6,6 -Diphenyl-2,3 -bipyridine is thought to be formed from... 

Pentaarylcyclopentadienols (375) are reported to yield endoperoxides (376) which when heated or treated with acids decompose to tetraarylfurans and the corresponding aryl acids.251 Tetraarylsubstituted cyclopentadienones such as tetracyclone (378) lead to m-diaroylstil-benes and carbon monoxide.252-255 Probably, as with other cyclopentadienes, endoperoxides are the primary products. However, no attempts seem to have been made to elucidate the mechanisms of rearrangements and decompositions involved in these reactions. 

Diethyldiphenylcyclopentadienone reacts with 3,5-dinitrophenyl azide on heating to give a pyrid-2-one in a similar reaction with phenyl azide, also suggested to proceed via the nitrene, a bridged intermediate (684) is formed (77TL2463). A different adduct (685) was isolated from the reaction between phthalimidonitrene and tetracyclone when treated with... 

Tetracyclone reacts with chromium hexacarbonyl to give black, air-sensitive products which contain no carbon monoxide groups, and are probably analogous to the cobalt complex (XXV) (215). 

Dienes react with molybdenum hexacarbonyl to give complexes of the type [Mo(CO)4(diene)] and [Mo(CO)2(diene)2], which are generally yellow, soluble in organic solvents, and readily sublimed. Cyclo-octa-1,5-diene (12, 79, 151), bicyclo[2,2,l]hepta-2,5-diene (175), a dimer of cyclo-octa-tetraene (12) and dimethyldivinylsilane (158) give the former type of complex with the structure (VI M = Mo), while butadiene (81) and cyclo-hexa-1,3-diene form the latter type (80). Tetracyclone gives the complex [Mo(CO)2(tetracyclone)2] (215). 

Substituted cyclopentadienones react with iron carbonyls to form stable, diamagnetic 7r-co triplexes of the type [Fe(CO)3(cyclopentadienone)] (215). The proposed structure is shown in (XX). These complexes undergo reactions typical of metal carbonyls, e.g., displacement of carbon monoxide by tertiary phosphines, but the carbonyl group of the ligand does not show reactions characteristic of a keto-group. These complexes are also formed by interaction of acetylenes with iron carbonyls (see Section VI,C). Interaction of tetracyclone and Fe3(CO)i2 gives unstable complexes which contain the sandwich anion [Fe(tetracyclone)2]2 analogous to the anion (XXV) (215). 

Tetracyclone reacts with dicobaltoctacarbonylmercury, [Co(CO)4]2Hg, to give the complex [Co(CO)2(tetracyclone)]2Hg, and with dicobaltocta-carbonyl to give the violet complex [Co(tetracyclone)2]2Co, which contains the sandwich anion (XXV) (215). Treatment of this complex salt with hydrochloric acid gives the ir-cyclopentadienyl derivative (XXVI). 

Nickel carbonyl reacts with tetracyclone to give the complex [Ni-(tetracyclone) 2] (215) and with duroquinone to give the complex [Ni-(duroquinone)2] (189). 

Manganese carbonyl, Mn2(CO)io, when treated with tetracyclone at 140-150°, gives an air-sensitive product which on hydrolysis gives the T-cyclopentadienyl complex (LII) 215). Manganese carbonyl does not react with dimcthylacetylene in sunlight, but duroquinone was formed in a similar reaction of the alkyne with [Mn(CO)6] 1 155). Mn(—1) is iso-electronic with Fe(0), and it is suggested that the unstable quinone com-... 

Nickel carbonyl does not react with dimethylacetylene in the presence of sunlight, but an alkaline solution of nickel carbonyl, which contains the ion [Ni(CO)3]2, yields hexamethylbenzene on similar treatment (155, 200). The nature of the intermediate 7r-complex is not known. Diphenyl-acetylene reacts with nickel carbonyl to give the dienone complex [Ni-(tetracycloned] (215) (see Section III,N). 

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