Indoline hydrogen donor

Nitrogen-containing heterocyclic compounds, including 1,2,3,4-tetrahydroqui-noline, piperidine, pyrrolidine and indoline, are also popular hydrogen donors for the reduction of aldehydes, alkenes, and alkynes [75, 76]. With piperidine as hydrogen donor, the highly reactive 1-piperidene intermediate undergoes trimer-ization or, in the presence of amines, an addition reaction [77]. Pyridine was not observed as a reaction product. 

Only little information is available on asymmetric ketone reduction using hydrogen transfer. With secondary alcohols or indoline as hydrogen donors, optical yields up to 9.9% were obtained in the presence of H4Ru4(CO)8[(-)DIOP]2 as a catalyst. Iridium compounds like [Ir(C0D)(PPEI)] C104 proved to be more enantioselective in the presence of Reducing propiophenone 30% e.e. was observed at 50%... 

Miscellaneous Reactions. The hydrogenolysis of chlorobenzene and the reduction of nitrobenzene occur in the presence of PdBr2 and indoline (the organic hydrogen donor) (eq 50). 

The scope of the method was later extended to indoHnes [121] however, as the previous optimized conditions failed to afford any acylated product, a fine-tuning of both the nucleophilic catalyst and the acyl donor appeared to be necessary. After intensive screening, the use of a bulkier cyclopentadienyl-derived catalyst such as 113 in conjunction with 0-acetylated azlactone 111 led to a more effective catalytic system, allowing the resolution of various indo lines with useful levels of selectivity ranging from s = 9.5 to 31 (Scheme 41.45). Most importantly, 2,3-disubstituted indolines, which are usually difficult to obtain in high ee by other methods such as the asymmetric hydrogenation of indoles, were also shown to be suitable substrates. 

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