Neutral Coordinate‐Organocatalysts in Organic Synthesis: Allylation of Acylhydrazones with Allyltrichlorosilanes

Abstract

N,N-Dimethylformamide (DMF), sulfoxides, and phosphine oxides, etc., which are neutral, uncharged molecules and coordinate to silicon atoms of organosilicon reagents to activate nucleophilic addition, are defined as neutral coordinate-organocatalysts (NCOs). In the presence of NCOs, allylation reactions of acylhydrazones, useful imine surrogates, using allyltrichlorosilanes proceed smoothly to afford the synthetically useful racemic and non-racemic homoallylic amine derivatives in high yields with high diastereoselectivities.

Evidence for an Enol Mechanism in a Highly Enantioselective Mannich‐Type Reaction Catalyzed by Primary Amine–Thiourea

“…N ‐Benzoylhydrazones have been used as substrates for several CC bond‐forming reactions;8 for example, the allylation8b and Mannich‐type reactions 8a,c–e. Kobayashi and co‐workers have recently developed several metal‐containing Lewis acid assisted catalytic, and stoichiometric, indirect stereoselective Mannich transformations of N ‐benzoylhydrazones that utilize preformed silyl enolate 8a,c–e.…”

Recyclable Polyisobutylene‐Bound HMPA as an Organocatalyst in Recyclable Poly(α‐olefin) Solvents

“…This reaction has been reported using HMPA as a catalyst and has been studied by others using polymer-supported formamides as catalysts so it provides a good way to evaluate the utility of this PIB-bound HMPA analog as an organocatalyst. [44,[48][49][50] We first compared the reactivity of 5 with HMPA in CH 2 Cl 2 in order to confirm that 5 acts like HMPA in this allylation chemistry (Scheme 2). We then examined the reactivity of 5 as an allylation catalyst in heptane and PAO 432 .…”

Stereospecific, Enantioselective Allylation of α‐Hydrazono Esters by Using Allyltrichlorosilanes with BINAP Dioxides as Neutral‐Coordinate Organocatalysts

“…Remarkably, the reactions proceeded without the use of any metal catalyst. These organic molecules coordinate to allyltrichlorosilanes to form hypervalent silicon compounds7 that react with electrophiles efficiently; thus, we defined these molecules as neutral coordinate‐organocatalysts ( NCO s) 8. Quite recently, we have achieved stereospecific, enantioselective allylation of N ‐acylhydrazones by using chiral sulfoxides as chiral NCO s 9.…”