Dual Palladium(II)/Tertiary Amine Catalysis for Asymmetric Regioselective Rearrangements of Allylic Carbamates

Abstract

The streamlined catalytic access to enantiopure allylic amines as valuable precursors towards chiral β- and γ-aminoalcohols as well as α- and β-aminoacids is desirable for industrial purposes. In this article an enantioselective method is described that transforms achiral allylic alcohols and N-tosylisocyanate in a single step into highly enantioenriched N-tosyl protected allylic amines via an allylic carbamate intermediate. The latter is likely to undergo a cyclisation-induced [3,3]-rearrangement catalysed by a planar chiral pentaphenylferrocene palladacycle in cooperation with a tertiary amine base. The otherwise often indispensable activation of palladacycle catalysts by a silver salt is not required in the present case and there is also no need for an inert gas atmosphere. To further improve the synthetic value, the rearrangement was used to form dimethylaminosulfonyl-protected allylic amines, which can be deprotected under non-reductive conditions.

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

“…75 Generally, substrates with α-aryl substituents gave rise to products with higher optical purity than these with α-alkyl analogues. The efficiency of the method is excellent for substrates forming fivemembered rings, but it dropped significantly for substrates forming a six-membered ring; tetrahydronaphthalene deriva- 7)-catalyzed [2 + 2] cycloaddition between 1,3-enynes (222) and ethylene followed by an enantioselective hydrovinylation of the resulting vinylcyclobutene (223) to give highly functionalized cyclobutanes (224) with an all-carbon quaternary stereocenter, as the (E)-isomer (Scheme 62). 76 The reaction proceeds in a tandem fashion to form three highly selective C−C bonds in one pot using a single chiral Co catalyst.…”

“…The use of an activator, Et 2 AlCl, was important to promote this cycloaddition reaction. The cycloaddition initiates with an oxidative dimerization of ethylene and the enyne (222) upon β-hydrogen elimination and reductive elimination finally leads to the (E)-224 isomer as the major product. The ratio of (Z)-and (E)-isomers depended on the nature of the R substituent and the nature of the ligand used.…”

“…219 Peters reported the regio-and enantioselective synthesis of sulfonyl-protected chiral allylic amines (596b) from achiral allylic alcohols (596a) by using a catalytic ferrocene palladacycle, [PPFOP-Cl] 2 (595a) and a tertiary amine (proton sponge -1,8-bis(N,N-dimethylamino)naphthalene) (Scheme 184). 221,222 This reaction was highly step-economic and proceeded with no inert-gas atmosphere or catalyst activation by a silver salt. The preference for the branched allylic product was due to the Pd(II)-catalyzed cyclization-induced decarboxylative [3,3]-rearrangement of in situ-generated allylic carbamate intermediates.…”

Synthesis of Stereoprojecting, Chiral N-C(sp3)-E Type Pincer Complexes

“…However, it allows the generation of synthetically challenging P,P- and P,N-bidentate ligands, which can develop five- or six-membered-ring chelation with the metal center, circumventing the hurdle of catalyst poisoning . Optically pure C­(sp 2 )-E (E = electron donor atom) type palladacycle complexes can be also successfully applied in catalytic amounts for asymmetric Michael-type addition reactions, including P–H addition, Hayashi–Miyaura arylboronic acid addition, [3,3]-sigmatropic aza-Claisen rearrangement, and ring-opening reactions just to name a few.…”

Synthesis of Enantioenriched γ-Amino-α,β-unsaturated Esters Utilizing Palladium-Catalyzed Rearrangement of Allylic Carbamates for Direct Application to Formal [3 + 2] Cycloaddition

“…The decarboxylative [3,3]-rearrangement of allylic carbamate is one of the most useful methods for the synthesis of allylic secondary amines, which are important building blocks in organic synthesis . The starting allylic carbamates can be easily prepared by treating the corresponding allylic alcohols with isocyanates, and the reaction generally proceeds under mild conditions by using transition-metal catalysts such as Pd­(II), Pd(0), Ir­(I), and Au­(I) complexes . Recently, as an application of this method to asymmetric synthesis, catalytic enantioselective reactions were developed in which achiral linear allylic carbamates were employed as substrates to provide chiral branched allylic amines having a monosubstituted alkene moiety. ,, We envisioned that allylic carbamates possessing an electron-withdrawing group at the allylic position would be applicable to this transformation to provide allylic amines having an electron-deficient alkene moiety that can function as a Michael acceptor (Scheme a).…”