Oxocarbenium Ion-Involved Cascade Reaction

OTMS (1)BC13,CH2CI2,0°Ctort (2)289e(10mol%) silyl ketene acetal (1.5 equiv) TBME,-78°C, 24 h 

SCHEME 2.83 Oxocarbenium ion-involved cascade reaction in the promotion of thiourea. 

4 BR0NSTEDACro AND TRANSITION METAL COOPERATIVELY CATALYZED CASCADE REACTIONS 

Over the past few decades, generally speaking, either metal salts or organic molecules have been used as efficient catalysts in promoting numerous asymmetric catalytic reactions in highly enantioselective fashion with different activation modes. However, a combination of the two types of catalysts with different but complementary characters makes it possible to explore new transformations through simultaneous or sequential activation by metal catalysts and organocatalysts, each of which alone failed to promote these transformations [2], In this chapter we focus on reactions that 

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Oxocarbenium Ion-Involved Cascade Reaction Reisman et al. also revealed that oxocarbenium ion derived from thiourea-assisted chloride dissociation of 1-chloroisochroman could be attacked by silyl ketene acetals 302 to generate esters 303 in an enantioenriched form (Scheme 2.83) [114]. 

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