Evolution

Read e-book online Cyclic Compounds PDF

By Boschke F.L.

ISBN-10: 3540056319

ISBN-13: 9783540056317

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L. Weber -e RIH ' ~ R 2 o D ~ R 3 0 239 R ~ -H *= m* Mo R2 9 0 (M~_I) 1 R l 1~ ~ m* R1 R2 1~ H R3 240 With 4,4-diacyl triafulvenes two principal fragmentation pathways have been observed ss). In 4-aroyl-4-acetyl triafulvenes 241 the molecular ion is followed by a fragment ion of probable "structure" 242 arising from primary loss of (CTH6R)', which surprisingly has incorporated a CH2 unit from the acetyl group and the exocyclic aryl residue. It is not unlikely that the (CTH6R)-residue corresponds to a substituted tropyl radical due to its well-known formation from electron-impact of benzylic precursors.

Likewise, the intermediacy of benzocyclopropenone (166, R = I-I) is claimed from spectroscopic evidence in the low-temperature photolysis of benzocyclobutene dione leading to benzyne 13Ob). ~ Ph Ph Ph Ph Ph Ph 176 177 ] 78 O Ar'matrix [ ~ = : 8"-O K O O -CO _-_ [ ~ 1 -CO III. Structural Criteria for Cyclopropenones and Triafulvenes 1. Basicity and Dipole Moment of Cyclopropenones and Triafulvenes a) Basicity Cyclopropenones can be isolated from the organic phase either by extraction or by precipitation with strong acid 42' 43) in the form of stable, often well-defined protonation products, the hydroxy cyclopropenium salts 1 79: R R " ~ R + HX ~ O R y X=BF4 +xe OH C104 HSO4 179 The basicity of cyclopropenones was determined by examining the disappearance of typical IR-absorptions (see p.

G. ] is apparently due to three-ring unsaturation. This means, however, that in contrast to Tobey's hypothesissa) (p. 31) the charge magnitude cannot be solely a function of the carbonyl group. 366) attributing a higher (§ to the centers CI/C 2 and the phenyl groups in the triafulvene than in the cyclopropenone. This is confirmed by XgF-NMR measurements of the p-fluoro-phenyl substituted species (see p. 48) and by the reactivity of the triafulvene 182 toward nucleophiles (see p. 90), which attack exclusively at ring carbons C1/C2 and not likewise at C3 as observed for the cyclopropenone 11.

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Cyclic Compounds by Boschke F.L.


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