Pictet transition state

Cook and col 1aborators (24) have shown that the Pictet-Spengler condensation of iminium salts of structure 56 (R=alkyl or aryl group) gave only the trans isomer 57 and in high yield. This result can be explained if the stereochemistry of the transition state corresponds to 58 59 where the principle... 

Apart from the reports mentioned above, there are sustainable monofunctional thioureas that successfully induce chirality. In 2007, Jacobsen and coworkers reported the enantioselective Pictet-Spengler cyclisation of hydroigrlactams. Utilising as little as 0.1 mol% of thiourea 10, indolizinone and quinolizinone products were afforded in high yields and high enan-tioselectivities (Scheme 19.14) via a counterion transition state. ... 

SCHEME 6.18 Transition state (TS-2 and TS-3) of the Pictet-Spengler cyclization. 

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