Highly Diastereoselective Multicomponent Cascade Reactions: Efficient Synthesis of Functionalized 1-Indanols

Jun Jiang, Xiaoyu Guan, Shunying Liu, Baiyan Ren, Xiaochu Ma, Xin Guo, Fengping Lv, Xiang Wu, and Wenhao Hu
Angew. Chem. Int. Ed.
DOI: 10.1002/anie.201208391


Wenhao Hu has been reporting remarkable reactions of transition metal-generated oxonium ylides for some time now. Oxonium ylides formed from alcohol insertion into carbenoids tend to undergo rapid 1,2-proton shift to give ethers (path A). However, Hu and coworkers report reactions where this process is delayed long enough for the ylide to react as a carbon nucleophile with electrophilic coupling partners (path B).


Recently, these oxonium ylides have been shown to undergo a cascade reaction with a dielectrophilic compound containing an unsaturated ester and an aldehyde. The ylide adds selectively to the Michael acceptor, which is followed by intramolecular aldol-type addition to the aldehyde to generate a complex indanyl adduct. The product is formed as a single diastereoisomer.


The group also report an asymmetric variant of the reaction using a chrial auxiliary on the diazo substrate.

Subsequent studies into the reaction attempted an intermolecular multicomponent cascade. Unfortunately, the product of 1,2-proton shift was preferred and no 4-component products were observed. More interestingly, the product of addition of the ylide into the unsaturated ester was only observed in 13% yield. This suggests that trapping of the oxonium ylide by the unsaturated ester in the dielectrophilic compound above is synergistically promoted by the presence of the aldehyde and subsequent aldol cyclisation.



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