Jorge R. Juárez

New methodology for the synthesis of enantiopure (3R,2aR)-(−)-3-phenyl-hexahydro-oxazolo[3,2-a]-pyridin-5-one: a synthesis of (S)-(+)-coniine

Abstract A new and efficient methodology for the enantiopure synthesis of (3R,2aR)-(−)-3-phenyl-hexahydro-oxazolo[3,2-a]pyridin-5-one 3 starting from (1′R)-(−)-1-(2′-hydroxy-1′-phenyl-ethyl)-(1H)-pyridin-2-one 1 is described. In addition, the enantiospecific synthesis of (S)-(+)-coniine hydrochloride 6 in good yield from 3 is reported.

A SHORT SYNTHESIS OF INDOLIZIDINE (+)-209B FROM (3R,6S,8aS)-(-)-6-METHYL-3-PHENYLHEXAHYDROOXAZOLO[3,2-a]-PYRIDIN-5-ONE

The synthetic potential of enantiopure (3R,6S,8aS)-(-)-6-methyl-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 2 is illustrated by a short synthesis of the 5,8-disubstituted indolizidine alkaloid (+)-209B.

The Zincke's Reaction: A New Alternative for the Preparation of L-[2-(3-Indol)Ethyl]-Alkylpyridinium Chloride Derivatives

Abstract The Zinckes salts 3 (a-f) were prepared and used for the synthesis of 1-[(2-(3-indol)-ethyl]alkylpyridinium chloride derivatives 5 (a-f) in high yields.

Synthesis of α-phenyl-1-(R)-(−)-piperidineacetic esters

Abstract Several α-phenyl-1-(R)-(−)-piperidineacetic esters 3(a-e), were obtained in pure enantiomeric form by condensing (R)-(−)-α-phenylglycine esters 2(a-e) with 1,5-dibromopentane. Similarly, (R)-(−)-α-phenylglycine esters, 2(a-e), were prepared from (R)-(−)-α-phenylglycine1 with high yields.

Reactivity of (1′ S )-1-(1′-phenyl-ethyl)-4-hydroxy-piperidin-2-one with Lawesson's reagent

The study of the reactivity of diasteromeric mixture (1′S)-1-(1′-phenyl-ethyl)-4-hydroxy-piperidine-2-one 2 with the Lawessons reagent in different conditions is described.

Diastereoselective Approach to cis-4-Methyl/thiol-Pipecolic Esters Based on RCM Reaction and Conjugate Michael Addition

Abstract A synthetic route for the access to enantiopure cis-4-methyl/thiol-pipecolic esters is presented. It is based on the ring-closing metathesis reaction to build the α,β-unsaturated piperidin-2-one derived from (S)-(–)-phenylethylamine, followed by either diastereoselective conjugate addition of methylorganocuprate allowing access to cis-4-methyl pipecolic ester or by tandem diastereoselective hydrosulforization–thionization reaction providing access to cis-4-thiol pipecolic ethyl esters. GRAPHICAL ABSTRACT

Regioselective Endocyclic Oxidation of Enantiopure 3‐Alkylpiperidines: Synthesis of (3S,5S)‐(‐)‐3‐Ethyl‐5‐Methylpiperidine

Abstract An efficient regioselective endocyclic oxidation of enantiopure 3‐alkylpiperidines 1(a–c) with bromine in acetic acid to generate the corresponding 5‐alkylpiperidin‐2‐ones 3(a–c) as main product is described. In addition, starting from 3a or 3b, the synthesis of (3S,5S)‐(‐)‐3‐ethyl‐5‐methylpiperidine 6 · HCl was achieved. Finally, the X‐ray single‐crystal analysis of compound 4 is reported.

Diastereospecific Intramolecular Cyclopropanation of Enantiopure 8-Bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-ones

A diastereospecific intramolecular cyclopropanation of (3R,8R,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 1 and (3R,8S,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 2 to generate the corresponding enantiopure 3-phenylhexahydro-5H-cyclopropa[3,4]pyrrolo[2,1-b]oxazol-5-ones 3 and 4 in high yield is described. The synthesis of chiral cyclopropanes remains a considerable challenge, especially due to the fact that cyclopropane rings are often found in a variety of natural products and biologically active compounds. Organic chemists have always been fascinated by the cyclopropane subunit which has played and continues to play a prominent role in organic chemistry. Its strained structure, interesting bonding characteristics and value as an internal mechanistic probe have attracted the attention of the physical organic community.1 Simmons-Smith cyclopropanation reaction is one of the most widely used reactions in the organic chemist’s arsenal for the conversion of olefins into cyclopropanes. This popularity is mainly due to the stereospecificity of the reaction with respect to the double bond geometry and its compatibility with a wide range of functional groups. The chemoselectivity of the reaction toward some olefins is excellent and very few side reactions are observed with functionalized substrates.2,3 Many of these reactions proceed in a cheletropic manner and several methods exist for converting alkenes to cyclopropane rings using carbene type reagents. As carbenes themselves are highly reactive it is common for them to be used in a stabilized form, referred to as carbenoid. The metal carbenoid is electrophilic in nature and electron-rich alkenes usually react much faster than electron-poor alkenes. In 152 HETEROCYCLES, Vol. 96, No. 1, 2018

(7aS)-(–)-Dimeth­yl(1-oxido-3-oxo-5,6,7,7a-tetra­hydro-3H-pyrrolizin-2-yl)sulfonium

In the zwitterionic title compound, C9H13NO2S, the pyrrolidine heterocycle adopts an envelope conformation (with the C atom in the 7-position as the flap). The negative charge is delocalized over the two carbonyl groups and the C atom connecting them. The positive charge is located on the S atom. Two intermolecular C—H⋯O interactions are observed. The molecular geometry at the S atom is trigonal pyramidal.

(S)-(−)-2-(1H-Indol-3-yl)-N-(1-phenyl­eth­yl)acetamide

In the title compound, C18H18N2O, the dihedral angle between the indole system and the phenyl ring is 17.2 (2)°. The crystal packing features two N—H⋯O hydrogen bonds, which link the molecules into layers parallel to (001). The absolute configuration was determined by the synthetic procedure and was set according to the starting material.