I. N. Alekseev

New chiral cyclopalladated complexes based on the pinane and bornane imines

Abstract2α-Hydroxypinan-3-one imino derivatives react with lithium tetrachloropalladate to form palladacycles, while similar bornane derivative undergo cyclopalladation only when treated with palladium acetate.

Oxidation of terpenoid diols with chlorine dioxide. Easy preparation of α-hydroxyketones

Oxidative dehydrogenation of vicinal diols of bornane and pinane type with chlorine dioxide in dimethylformamide has yielded α-hydroxyketones with high selectivity. 3α-Hydroxy-10β-pinane-4-one has been prepared for the first time with yield of 63–65%; the product structure has been confirmed by X-ray diffraction studies.

Oxidation of terpenoid diols with chlorine dioxide: Preparation of ketols and α-chlorohydroxyketones of carane and pinane structures

Vicinal terpenoid diols of carane- and pinane-type structures have been oxidized with chlorine dioxide in pyridine to form the corresponding ketols in the preparative yield of 52–72%, the selectivity of α-hydroxyketones formation being 80–90%. It has been shown that the diols reactivity towards oxidation with ClO2 depends mainly on the stereochemistry of hydroxy groups. The catalysts, VO(acac)2, Mo(CO6), and MoCl5 have practically no effect on the oxidation process. When the reaction has been performed in dimethylformamide, the hydroxyketone chlorination occurred at high conversion.

Heterocyclization of 3-aminocamphor and 3-aminoisoborneol derivatives with cyclic β-diketones and formaldehyde. Synthesis of optically active 1,2,3,4-tetrahydroquinoline derivatives with terpene substituents

Spirocyclic 1,2,3,4-tetrahydroquinoline derivatives were prepared in quantitative yield by three-component condensation of dimedone or Meldrum’s acid with formaldehyde and (1S,3R,4S)-1,7,7-trimethyl-3(arylamino)bicyclo[2.2.1]heptan-2-one or (1S,2S,3R,4S)-1,7,7-trimethyl-3-(arylamino)bicyclo[2.2.1]heptan2-ol.

Chiral palladium complexes with monoterpenoids oximes

Oximes of cis-caran-4-one, 3α- and 3β-hydroxycaran-4-ones, cis-verbanone, menthone, and 2β-hydroxybornan-3-one have been synthesized. The obtained oximes react with lithium tetrachloropalladate to give new chiral palladium complexes containing mono-or bidentate oxime ligands.

Several Monoterpenoid Bromination Products

2α-Bromo,10β-pinanone-3 and 3α-bromo,10β-pinanone-4 were formed with 92–98% selectivity by bromination of isopinocamphone and cis-verbanone with Meldrum’s acid dibromide. 3α-Bromo, 10β-pinanone-4 was prepared for the first time. Its structure was confirmed by an XSA. Bromination of menthone by Meldrum’s acid dibromide formed mainly a mixture of diastereomeric 2-bromomenthones in a 2:1 ratio. Oxidative bromination of isopinocampheol by Ce(III)–LiBr–H2O2 caused rearrangement of the pinane structure into bornane and formed a mixture of 6-endo- and 6-exo-bromocamphor in a 5:1 ratio.

Synthesis of new bidentate ligands—terpene derivatives of ethylenediamine and their palladium complexes

New enantiomerically pure Schiff bases and palladium chelates based thereon were synthesized starting from (–)-α-pinene or (‒)-camphor and N,N-dimethylethane-1,2-diamine.

Reactions of terpene alcohols and diols with chlorine dioxide in dimethylformamide

The system chlorine dioxide–dimethylformamide in combination with or without a catalytic amount of MoCl5, CeCl3, ZrOCl2, or VO(acac)2 induces oxidative chlorination of a number of bicyclic terpene alcohols and vicinal diols. 2α-Chloropinan-3-one, 3α-chloro-10β-pinan-4-one, 5α-chloro-3α-hydroxycaran-4-one, 5β-chloro-3β-hydroxycaran-4-one, and 4α-chloro-2α-hydroxypinan-3-one were thus synthesized in good preparative yields.

Synthesis of new enantiomerically pure β-amino alcohols of the pinane series

A series of new β-amino alcohols with pinane structure, (+)- and (‒)-3α-amino-10β-pinan-4β-ols, 4β-amino-10β-pinan-3α-ol, and 4α-amino-10β-pinan-3α-ol have been synthesized with the goal of using them as organocatalysts in the aldol reaction of isatin with acetone.

Stereoselective synthesis of amino ketones of the pinane series

At present, enantiomerically pure α-pinene and camphor derivatives are widely used in asymmetric syntheses as chiral auxiliaries [1], building blocks [2, 3], and chiral ligands [4]. For example, terpene amino alcohols derived from 2α-hydroxypinan-3-one, were studied as enantioselective ligands in the ruthenium-catalyzed reduction of acetophenone [5], while palladium chelates with bornane diimines and diamines efficiently catalyzed asymmetric allylic substitution reactions [6]. According to published data, search for new enantiomerically pure ligands on the basis of commercially available initial compounds is a topical problem. We previously reported the synthesis of chiral imines and amines from 2α-hydroxypinan-3-one [7]. The resulting nitrogen-containing derivatives were successfully used as ligands to obtain various palladium complexes [8, 9].