Hans Leijonmarck

Dynamic Kinetic Asymmetric Domino Oxa‐Michael/Carbocyclization by Combination of Transition‐Metal and Amine Catalysis: Catalytic Enantioselective Synthesis of Dihydrofurans

A one-pot highly chemo- and enantioselective catalytic domino oxa-Michael/carbocyclization between α,β-unsaturated aldehydes and propargylic alcohols is presented. This dynamic kinetic transforma ...

Direct Catalytic Asymmetric Synthesis of Pyrazolidine Derivatives

A highly enantioselective, metal-free cascade reaction between di-1,2-N-protected hydrazine and α,β-unsaturated aldehydes is disclosed. The catalytic, asymmetric cascade transformation is a direct ...

Intramolecular Claisen-type condensations of β-acetoxy amides or imides

Abstract Intramolecular Claisen-type condensation of amide 1 or imide 7 leads to the same δ-lactone in racemic ( 2 ) or enantiomerically pure form ( 4 ) respectively. A side-reaction producing the 11-membered ring compound 6 makes imide 3 unsuitable as a starting material for the synthesis of 4 . A clean two-step reduction of 4 to 9 is also described.

Studies on the intramolecular Claisen condensation. Stereospecific ring-closure of β-acetyloxy esters

On treatment with lithium bis(trimethylsilyl)amide, α-alkyl-β-acetyloxy esters (2) and (3) undergo stereospecific ring-closure to the 5,6-dihydro-4-hydroxy-2H-pyran-2-ones(2,4-dioxotetrahydropyrans)(4) and (5).

A versatile and concise route to carbocycles using a 1,6-electrocyclic reactionElectronic Supplementary Information (ESI) available: experimental section. See http://www.rsc.org/suppdata/cc/b3/b311815k/

The viability of the 1,6-electrocyclic route to 1,3-cyclohexadienes has been significantly increased by using a phenylsulfonyl substituent in a multi-purpose (≥3) role.

Friedel–Crafts reactions of a sulfonyl-substituted vinylic epoxide with various aromatics

The phenylsulfonyl-substituted vinylic epoxide 1 was allowed to react with BF3·OEt2 and various aromatics. A highly regioselective but moderately stereoselective mono-Friedel–Crafts reaction occurred which led to products 2 (Table 1). The fluorine-containing compounds 3a–b and 4 were obtained as side products.

Preferential formation of five-membered rings in two Claisen cyclisations

α-Lithiations of the acetoxy groups of 1 and 2 lead to Claisen cyclisations in which five-membered rings are formed much faster than six-membered rings; this selectivity is opposite to that of aldol condensations.