Alkylation Morita-Baylis-Hillman carbonate

Chen and coworkers published a formal [3 + 3]-type reaction to give highly substituted cyclohexenes 8. This domino process consists of an allylic-allylic alkylation of an a,a-dicyanoalkene derived from 1-indanone and Morita-Baylis-Hillman carbonates, following an intramolecular Michael addition, by employing dual orga-nocatalysis of commercially available modified cinchona alkaloid (DHQD)2AQN If (hydroquinidine (anthraquinone-l,4-diyl) diether) and (S)-BINOL. The cyclic adducts... 

Chen and coworkers employed the cinchona alkaloid-derived catalyst 26 to direct Mannich additions of 3-methyloxindole 24 to the A-tosylimine 25 to afford the all-carbon quaternary center of oxindole 27 with good enantioselectivity (84% ee) [22]. The outcome of this Mannich reaction is notable in that it provided very good selectivity for the anti diastereomer (anti/syn 94 6). The mechanism of asymmetric induction has been suggested to involve a hydrogen bonding network between the cinchona alkaloid 26, the oxindole enolate of 24, and the imine electrophile 25 (Scheme 7). Asymmetric allylic alkylation of oxindoles with Morita-Baylis-Hillman carbonates has been reported by the same group [23]. 

In 2009, Chen et al. reported the first highly enantioselective allylic-allylic alkylation of a,a-dicyanoalkenes with Morita-Baylis-Hillman carbonates by dual organocatalysis of commercially available modified cinchona alkaloids and S)-BINOL. Excellent stereoselectivities were achieved for a broad range of substrates by using hydroquinidine (anthraquinone-l,4-diyl) diether ((DHQD)2AQN) as the cinchona alkaloid. Indeed, in all the cases studied, only one diastereomer was isolated with both excellent enantioselectivity and yield, as shown in Scheme 5.9. 

An asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates and )0-keto sul-fones by modified cinchona alkaloids as catalysts gives products that undergo a Smiles rearrangement-sulfinate addition cascade to functionalized five-membered cyclic sul-fones (Scheme 172) ... 

DHQD)2AQN (17) and 18 resulted in excellent enantioselectivity (95% ee) and isolated yield (97% yield). The scope of the allylic-allyUc alkylation of a,a-dicyanoalkenes and Morita-Baylis-Hillman carbonates was explored and excellent results were obtained by the dual catalysis of 17 and 18. In most cases, excellent stereoselectivities have been achieved for a broad spectrum of substrates (dr > 99 1, up to 99% ee). 

Scheme 43.3 Allylic-allylic alkylation of a,a-dicyanoalkenes and Morita-Baylis-Hillman carbonates by dual organocatalysis.

A Lewis base-assisted Brpnsted base catalysis strategy has been used for direct asymmetric vinylogous alkylation of allylic sulfones with Morita-Baylis-Hillman (MBH) carbonates, in which a strong Brpnsted base, f-butoxy anion, generated in situ from a tertiary amine catalyst and MBH carbonate, is crucial in activating unstabilized nucleophiles. The y-regio-selective alkylation products were obtained with good to excellent enantiomeric excess (up to 98% ee) values when catalysed by a modified cinchona alkaloid. 

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