Indoline ring moiety

The intermolecular variant of the above reaction between W-methylphthalimide (74) and a series of W-acylindole derivatives 75a-f was next examined [37, 38]. Compounds 75a and 75d-f produced the corresponding more sterically hindered oxetanes 76a and 76d-f in which the aromatic rings of the isoindolone and indoline moieties overlap (Scheme 19). Interestingly, in the cases of 75b, c, the initially formed oxetanes 76b-d were converted to a variety of products, presumably via the hydrolysis of the oxetanes, followed by ring opening of the indoline ring and subsequent reactions to produce 78-81. 

In Grigg s approach to hippadine (37), he established the connection between the two phenyl rings via the Stille-Kelly reaction [45]. When diiodide 35 was submitted to the Pd(0)/ditin catalyst system, the intramolecular cyclization was realized to establish the C—C bond in lactam 36. Oxidation of the indoline moiety in 36 using 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) then delivered hippadine (37). Analogously, the intramolecular Stille coupling of dibromide 38 led directly to hippadine (37) [46]. 

In the case of compound 19, the indoline and naphthoxazine moieties are linked by a bridged chain the configuration is relatively rigid even after cleavage of the C-0 in the oxazine ring. The ring-opened species can be observed in acetonitrile, but not in cyclohexane.15 The synthesis of compound 19 is given later. 

The structure of the piperidine moiety and the presence of an unsubstituted tryptamine bridge in alkaloids of the mavacurine-pleiocarpamine class can be proved by a catalytic reduction to the corresponding indolines, which show very different spectra because now the main fragments contain ring D,los (212)- -(216)- -[2I7]-> [218]->[219]. The reduction of indole to indoline alkaloids seems an attractive route for the structure determination of those alkaloids.25... 

The indole alkaloids so far discussed all have a tetrahydro-/ -carboline system. The main fragments of these alkaloids contain the indole part of the molecules. This situation is changed in alkaloids which have a larger ring C or an indoline system, permitting the production of fragments characteristic of both the indole and piperidine moieties. 

The reactivity (photodegradation) of spiropyrans substituted on the aromatic ring of the indoline moiety has been rationalized in terms of inductive and mesomeric effects and quantified on the basis of the Hammett equation ... 

Vl/2 values. For substituents on the benzopyran ring, the o values were those used by the National Cash Register Company (NCR). Taft or McDaniel and Brown values28 were used for substituents on the indoline moiety for 5-substituted pyrans, CTpara values were found to be adequate. 

No major improvement of photodurability was observed on going from the five- to the six-membered ring azaheterocyclic spiropyrans.32 In the piperidine series, a methyl group at C3 diminishes photostability by a factor of, 2 (Table 12, 142 vs. 144). The introduction of electron-acceptor atoms such as sulfur and oxygen at the position 3 to the nitrogen atom of the azaheterocycle results in a decrease of the photostability of the modified spiropyran. On the other hand, the indoline series compounds are more photostable than the pyrrolidinospiropyrans. As noted previously, electron-donor groups (e.g., CH3) on the azaheterocyclic moiety increase photostability. 

The cyclization of an aryl radical is a useful process for the preparation of (hetero)cyclic compounds such as tetrahydrobenzofurans, chromanes, indanes, indolines and tetrahydroquinolines [147]. The synthetic strategy involves the generation of an aryl radical which subsequently adds to an unsaturated moiety, most usually in a 5-exo or a 6-exo trig process (Scheme 13.19). After ring closure, the intermediate cyclized radical 93 can either be reduced (pathway A) or it can react further with a nucleophile (SRNl-type process, pathway C) or with another radical acceptor to yield, after reduction, compounds of type 94 (pathway B). 

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