Highly Enantio- and Diastereoselective Allylic Alkylation of Morita–Baylis–Hillman Carbonates with Allyl Ketones

Abstract

The asymmetric allylic alkylation of Morita-Baylis-Hillman (MBH) carbonates with allyl ketones has been developed. The α-regioselective alkylation adducts, containing a hexa-1,5-diene framework with important synthetic value, were achieved in up to 83% yield, >99% ee, and 50:1 dr by using a commercially available Cinchona alkaloid as the catalyst. From the allylic alkylation adduct, a cyclohexene bearing two adjacent chiral centers was readily prepared.

Direct Catalytic Enantioselective Vinylogous Aldol Reaction of Allyl Ketones to Pyrazole-4,5-diones

“…While Brønsted basic tertiary amine moiety of the catalyst was expected to enolize allyl ketones through removal of its acidic α-proton, LUMO-lowering activation of pyrazole-4,5-diones was envisaged through H-bonding from the Brønsted acidic part of the catalyst. We were cognizant of the potential regioselectivity issues associated with this reaction and the mixed (α- vs γ-) selectivity previously observed under the influence of similar catalyst systems . Nonetheless, considering the sterically hindered nature of the electrophilic site at the C-4 of pyrazole-4,5-diones, we believed the proposed catalyst system would favor the desired vinylogous reactivity of allyl ketones.…”

Extended Enolates: Versatile Intermediates for Asymmetric C‐H Functionalization via Noncovalent Catalysis

“…[101] On the other hand, addition of transiently generated dienolates to MBH carbonates was shown feasible upon activation of these latter by Lewis base (nucleophilic) catalysts. For instance, Huang and Jiang reported [102] the α-selective addition of allyl aryl ketones 82 (R 1 = aryl) to MBH carbonates 164 in the presence of 10 mol% (DHQD) 2 PYR to afford adducts 165 in generally good yields and high selectivity (Scheme 42). The tBuO À anion detached upon coupling of the tertiary amine catalyst with the MBH adducts is postulated to act as a base for dienolate formation.…”

Asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with α-fluoro-β-keto esters

“…Lewis base-catalyzed asymmetric allylic alkylations (AAA) of Morita–Baylis–Hillman (MBH) adducts [5–6], such as acetates and carbonates, have become an attractive option to access various chiral C - [7–19], N - [20–25], O - [26–30], P - [31–33] and S -allylic [34] and spirocyclic compounds [35–37]. Several protocols have been established to introduce fluorine atoms in AAA of MBH adducts.…”