Indene ring system

When the ring system containing the sulfone moiety is unsaturated, a quite different set of products has been observed on photolysis, apparently arising from an initial cycloreversion to a short-lived sulfene intermediate. For example, irradiation of 2H-1-benzothiopyran 1,1-dioxide (41) in dichloromethane or methanol gave the cis- and trans-sultines (42) and the ring-expanded sultine (43) in roughly equal amounts, accompanied by minor amounts ( 5%) of the products of formal loss of S02, i.e. indene, and SO, i.e. 4472... 

Although only a few condensed 5 6 or 5 5 aromatic pyrazole derivatives can be isolated from biological sources, the chemistry of condensed pyrazoles has received considerable interest. Condensed pyrazoles with an indene skeleton can be considered as purine analogues and, as such, are expected to have biological activity. The discovery of the xanthene oxidase inhibitory action of pyrazolo[3,4-fiT pyrimidine and the cAMP phos-phodiasterase inhibitory action of pyrazolo[l,5-a]pyrimidines has stimulated considerable interest in the synthesis of analogues of both ring systems. 

Other bicyclic ozonide examples are given in Scheme 37. The number of examples available reflects the inherent stability of this type of trioxolane ring system. The x-ray structures of several of these 1,2,4-trioxolanes have been discussed in Section 4.16.3.1. Substituted indene derivatives... 

Photodimerization of the stilbene chromophore in small or medium ring systems is highly dependent upon the ring size. Indeno[2,l-a]indene (5) yields a 1 2 mixture of head-to-head head-to-tail dimers 28 and 29 (eq. 12) upon irradiation in... 

In order to facilitate comparisons between different rings systems, the base components indene, indacene, pentalene, and naphthalene have been chosen for the design of the carbocyclic pattern of the tricyclic assembly (Table 2). Of these broad classes of structures, [/lannelated- (1), [e]annelated-(5), [a]annelated- (2), and [c,d]annelated-indenes (6) have been the most completely explored, less being known of (l,4)-methano-naphthalenes (7), while [c]annelated- (3), [bridged systems (8-10) and the (3a,6a)-butano-pentalenes (11) have been scarcely mentioned, if at all, in CHEC-I. 

Bergson et /.i4 i8,247.248.3i4 using mr spectrometry and polarimetry as analytical techniques, made a detailed study of the kinetics and mechanisms of base-catalyzed isomerization, racemization, and mutarotation reactions of 1-substituted and 1,3-disubstituted indenes. The prototropic rearrangements are completely stereospecific and intramolecular when aliphatic amines are used as catalysts in solvents of low or moderate polarity— the proton becomes re-attached to the same side of the ring system from which it departed under these conditions With alcohols as solvents and alkoxides as catalysts, extensive racemization occurs indicating that indenes form symmetrically solvated carbanions in alcohol solvents. In dimethyl sulfoxide, isomerization was only partly stereospecific even when aliphatic amines were used as catalysts. These, and other observations, are rationalized by the reaction scheme... 

The reaction appears to be a 1,5-shift of carbon to an isomer of indene followed by a 1,5-hydrogen shift. The activation energy is roughly 10 kcal/mol less than that for rearrangement of spiro[4.4]nona-l,3-diene to the same bicyclic ring system (see Section 3.9) suggesting substantial involvement of the second tt system in the 1,5-carbon shift. Further evidence for tt participation in bond making comes from a comparison of the rates of 1,5-carbon shift in spiro[4.4]nona-l,3,6-triene its 1,3,7-isomer (Scheme 10.7). 

Substitutions in the six-membered rings of indenes are considerably more difficult to access synthetically. In most cases, constmction of the entire indenyl ring system from smaller building blocks is required and the desired ligands are obtained in low overall yields. As an example, the... 

The question remains why do two such closely related groups of compounds produce such markedly different Br nsted plots Fluorenes and indenes are derivatives of cyclopentadiene and one wonders if the magic properties of 4n + 2 ring systems are responsible. 

An interesting ladder polymer that has recently been prepared is shown as structure 52(p,m) (R = P-C10H21-CeH4 and R = CeHn) [89,90], where indene-type ring systems are fused in what has been termed a (p,/w) configuration [86]. The p and m (para and meta) describe the relationship of the nonbenzenoid carbons around the six-membered rings. The calculated band gap for this... 

Particularly, benzofused Cp derivatives such as indene and fluorene had serious impact on the development of catalyst precursors for stereospecific olefin polymerization [17]. However, fusing aromatic ring systems to the cyclo-pentadienyl ring can sometimes cause problems with regard to the bonding situation between metal and ligand because the tendency of the benzofused ring to preserve its aromatic six-electron system leads to a haptotropic shift as depicted in Scheme 6.2. 

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