Catalytic Asymmetric Allylation of Aldehydes and Related Reactions with Bis(((S)‐binaphthoxy)(isopropoxy)titanium) Oxide as a μ‐Oxo‐Type Chiral Lewis Acid

Abstract

A new, chiral bis-Ti(IV) oxide of type 3 has been designed and can be utilized for strong activation of aldehyde carbonyls, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin. The chiral bis-Ti(IV) catalyst (S,S)-3 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide with (S)-BINOL or by treatment of ((S)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. Treatment of hydrocinnamaldehyde with allyltributyltin under the influence of chiral bis-Ti(IV) oxide (S,S)-3 generated in situ (10 mol %) in CH(2)Cl(2) afforded an allylation product in 84 % yield and with 99 % ee. This asymmetric allylation with non-racemic bis-Ti(IV) oxide 3 and partially resolved (S)-BINOL shows a positive nonlinear effect in correlation of the enantiopurity of the allylation product with the ee of the (S)-BINOL. Chiral bis-Ti(IV) oxide (S,S)-3 can also be utilized for related reactions such as asymmetric methallylation and propargylation of aldehydes with high enantioselectivity. This asymmetric approach provides a very useful way of obtaining high reactivity and selectivity through the simple introduction of the M-O-M unit into the design of chiral Lewis acid catalysts.

Nonlinear Effects in Asymmetric Catalysis

“…[71] The presence of a (À)-NLE with triple-shaped curves led the authors to suggest the involvement of tetrameric species on the basis of previous predictions of multishaped NLEs curves in ML 4 models by mathematical simulations. [10] Bandini et al [71] hypothesized the involvement of a catalytically active dimeric aggregate [(59) Maruoka and co-workers [72,73] prepared a binolate-Ti IV catalyst 61 for asymmetric allylation with allyltributyltin [Eq. (16)].…”

Asymmetric Propargylation of Ketones Using Allenylboronates Catalyzed by Chiral Biphenols

“…2 However, few methods exist to prepare them in enantioenriched form. Chiral allenyl metal reagents have proven effective 3,4 and recently described catalytic approaches 5,6,7 are notable alternatives for accessing these chiral synthetic intermediates. As a reagent for propargylation reactions, allenylboronates are attractive starting materials due to ease of preparation and predictable reactivity patterns.…”

A Concise Total Synthesis of (+)‐Neopeltolide

“…[8] Nonetheless, the CM should still be challenging owing to an intrinsically competitive RCM initiated at the C2ÀC3 double bond to form a six-membered carbocycle. Finally, substrate 7 would be synthesized from the known homoallylic alcohol 8, [9] which is available from (E)-cinnamaldehyde by an asymmetric allylation.…”