Catalytic Asymmetric Disulfuration by a Chiral Bulky Three‐Component Lewis Acid‐Base

Abstract

A three‐component Lewis acid–base (Lewis trio) involving a bulky chiral primary amine, B(C6F5)3 and a bulky tertiary amine has been developed as an effective enamine catalyst for enantioselective disulfuration reactions. The bulky tertiary amine was found to activate a bulky primary–tertiary diamine–borane Lewis pair for enamine catalysis via frustrated interaction. The resulted chiral bulky Lewis trio (BLT) allows for the construction of chiral disulfides via direct disulfuration with β‐ketocarbonyls or α‐branched aldehydes in a practical and highly stereocontrolled manner.

Decatungstate-catalyzed radical disulfuration through direct C-H functionalization for the preparation of unsymmetrical disulfides

“…Considering C-SS bond formation, that approach has benefited from the development of electrophilic and nucleophilic “masked” disulfuration reagents 25 , 26 . These transformations proceed through metal-catalyzed cross-coupling 27 , 28 or substitution reactions 15 , 29 – 31 . It is worth mentioning that in these disulfuration processes, one reaction component carries both sulfur atoms rendering such methods valuable for the preparation of unsymmetrical disulfides.…”

Synergistic Strategies in Aminocatalysis

“…Primary-tertiary amine catalyst 31, already successfully employed for other non-synergistic transformations involving highly sterically demanding carbonyl compounds, [13] afforded 30 in good yields and excellent ee (Scheme 6). [14] Interestingly, catalytic amounts of the external tertiary amine 33 resulted as well crucial, improving both the yield and the stereoselectivity of the reaction, while the use of TfOH instead of 32 was detrimental. In the proposed transition state, chiral amine 31 activates 28 through HOMO-raising.…”

Direct activation of alcohols via perrhenate ester formation for an intramolecular dehydrative Friedel–Crafts reaction

“…The direct application of alcohols as alkylating reagents is attracting increasing attention from the academic society and many innovative activation modes for alcohols have been invented. 5–9 Re 2 O 7 -mediated direct activation of reactive alcohols was realized when stable carbenium ions were formed (Fig. 1B); 10,11 however, debates exist over whether these reactions proceed through perrhenate ester formation or through Brønsted acid-catalyzed dehydration.…”