Reactivity of 1,2-cyclic sulfite xylosides towards nucleophiles

1,2-Cyclic sulfite xylosides offer facile access to 1,2-oxazolines upon reaction with aromatic and alkyl nitriles under Lewis or Brönsted acid conditions. Additionally, hydrophobic ionic liquids facilitate acid-catalysed formations of such oxazolines and C- and O-linked xylosides, providing means to carry out fast reactions at room temperature, and this in yields comparable to reactions conducted in xylene at high temperature for extended reaction time.     

Enzymatic resolution of sec-butylamine

Resolution of (±)-sec-butylamine by Candida antarctica lipase provided a very low enantiomeric excess of the residual amine when either ethyl or vinyl butyrate was used as the acylating agent. The enantiomeric excess was increased by using ethyl esters of long chain fatty acids. The rate of the reaction was increased by using methyl t-butyl ether as a solvent. (S)-sec-Butylamine of very high enantiomeric excess was obtained by C. antarctica lipase catalyzed acylation with ethyl decanoate in methyl t-butyl ether.     

1,2-cyclic sulfamidates as versatile precursors to thiomorpholines and piperazines

[reaction: see text] 1,2-Cyclic sulfamidates undergo regiospecific nucleophilic displacement with either methyl thioglycolate or alpha-amino esters, followed by lactamization (thermal, base-mediated, or cyanide-catalyzed), to give thiomorpholin-3-ones and piperazin-2-ones.     

Enantiopure 1,4-benzoxazines via 1,2-cyclic sulfamidates. Synthesis of levofloxacin

1,2-Cyclic sulfamidates undergo efficient and regiospecific nucleophilic cleavage with 2-bromophenols (and related anilines and thiophenols), followed by Pd(0)-mediated amination to provide an entry to substituted and enantiomerically pure 1,4-benzoxazines (and quinoxalines and 1,4-benzothiazines). This chemistry provides a short and efficient entry to (3S)-3-methyl-1,4-benzoxazine 19, a late stage intermediate in the synthesis of levofloxacin.     

Enzymatic resolution of flavanone oximes

The optically active (R)- and (S)-flavanones were prepared by an enzymatically enantioselective hydrolysis of (±)-flavanone oxime O-acylates employing lipases, followed by hydrolysis with acid.     

Enzymatic kinetic resolution of ketorolac

Ketorolac 1 was resolved into each enantiomer by interesterification using lipase B from Candida antarctica. The acid reacted with various alcohols and the ester and acid were resolved up to >99% e.e. when reacted with octanol, which was the best result. To increase reactivity and enantioselectivity, the experimental conditions were adjusted by varying temperature, solvent, alcohols and reaction time.     

Enzymatic resolution of racemic lactones

PPL, HLE or PLE enzymatic resolution of racemic γ, δ and ε-lactones gives optically active lactones (ee: 60 to 90%).     

Enzymatic resolution of 2-trifluoromethylalanine

Hog kidney aminoacylase catalyzes hydrolysis of N-trifluoroacetyl-R(+)2-trifluoromethylalanine with 99.1% enantioselectivity.     

碱性离子液体催化甘油合成1,2-甘油碳酸酯(英)

以离子液体为催化剂,在无溶剂体系中,考察了生物质平台化合物甘油转化1,2-甘油碳酸酯的反应.与酸性离子液体和常用无机碱性催化剂相比,碱性离子液体咪唑基1-丁基-3-甲基咪唑([Bmim]Im)、氢氧化1-丁基-3-甲基咪唑([Bmim]OH)、咪唑基1-烯丙基-3-甲基咪唑([Amim]Im)、氢氧化1-烯丙基-3-甲基咪唑([Amim]OH)在甘油与碳酸二甲酯的酯交换反应中表现出优异的活性.其中,以[Bmim]Im离子液体为催化剂时甘油转化率为98.4%和甘油碳酸酯选择性接近100%.另外,该离子液体可以回收重复利用3次后甘油转化率仍可达92%,甘油碳酸酯选择性可近100%.此碱性离子液体催化方法具有反应结果较好、产物分离简单、条件温和以及环境友好等特点.     

Cationic polymerization of a derivative of allylamine and 1,2-naphthoquinone

Cationic polymerization of a monomer derived from allylamine and 1,2-naphthoquinone was studied by polarography. The optimum conditions and kinetic characteristics of the process were found.     

Enzymatic kinetic resolution of tropic acid

A new strategy has been developed for the CAL-B catalysed kinetic resolution of tropic acid by which both enantiomers of tropic acid can be obtained in good enantiomeric excess. (R)-Tropic acid was synthesised with 90% ee and (S)-tropic acid butyl ester in 99% ee by the hydrolysis of tropic acid butyl ester. The other enantiomers were available through the enzymatically catalysed reaction of tropic acid lactone with butanol to give (S)-tropic acid lactone and (R)-tropic acid ester in >98% ee.     

Enzymatic kinetic resolution of Morita-Baylis-Hillman acetates

Racemic Morita-Baylis-Hillman adducts derived from the reaction of acrylonitrile with benzaldehyde, cinnamaldehyde and hydrocinnamaldehyde have been successfully resolved by means of enzymatic kinetic resolution. The (+)-alcohol products were isolated with 94–97% ee after lipase-mediated enantioselective hydrolysis of the corresponding acetates. Mosher’s double derivatisation protocol was applied to these isolated products and the absolute configuration of the alcohols was found to be (S) for all three substrates.     

Enzymatic resolution of chiral phosphinate esters

The bacterial phosphotriesterase has been shown to catalyze the stereoselective hydrolysis of phosphinate esters. The wild-type enzyme preferentially hydrolyzes the SP-enantiomers of methyl phenyl p-X-phenylphosphinate esters by 3 orders of magnitude. The mutant enzyme, I106T/F132A/H254G/H257W, exhibits the opposite stereoselectivity and hydrolyzes the RP-enantiomer up to 30 times faster than the corresponding SP-enantiomer. The enantiomerically pure phosphinate esters, prepared from the kinetic resolution of racemic mixtures, can serve as the entry point for the chemoenzymatic preparation of P-chiral phosphines and phosphine oxides.     

Enzymatic optical resolution via acylation-hydrolysis on a solid support

By taking advantage of the reversibility of the thermolysin-catalysed amide synthesis-hydrolysis reaction on a solid support, both L,L and L,D diastereoisomers of dipeptides and L-amino acids are accessible in good yields starting from enantiomeric mixtures of amino acids.     

Enzymatic resolution of substituted mandelic acids

A series of substituted mandelic acids were prepared and subjected to enzymatic resolution utilizing Lipase PS ‘Amano’.     

Stereoselective synthesis of cis-2,6-disubstituted piperidines from 1,2-cyclic sulfamidates

Diastereoselective synthesis of cis-2,6-disubstituted piperidines from 1,2-cyclic sulfamidates is described. Regioselective ring-opening reactions of 1,2-cyclic sulfamidates derived from L-phenylalanine, alanine, valine, norvaline with the ketal protected acetylide with a phenyl substituent proceed smoothly to form the N-sulfamate intermediates which on acidic hydrolysis give alkynylated amines with the ketal group intact. Hydrogenation of the alkynylated amines, debenzylation, ketal deprotection, subsequent cyclization (of aminoketones) and stereoselective hydrogenation of the cyclic iminium ion intermediates afford the corresponding cis-2,6-disubstituted piperidines in high diastereoselectivity (98%?≥?d.e.) with good chemical yields (68–86%). The present approach provides a novel route for the stereoselective synthesis of cis-2,6-disubstituted piperidines.     

Site-selective catalysis: toward a regiodivergent resolution of 1,2-diols

This paper demonstrates that the secondary hydroxyl can be functionalized in preference to the primary hydroxyl of a 1,2-diol. The site selectivity is achieved by using an enantioselective organic catalyst that is able to bond to the diol reversibly and covalently. The reaction has been parlayed into a divergent kinetic resolution on a racemic mixture, providing access to highly enantioenriched secondary-protected 1,2-diols in a single synthetic step.     

Enzymatic resolution of stereoisomers of 2-iodocyclohexanol

All four optically active stereoisomers of 2-iodocyclohexanol were synthesized. Their enantiomeric purity was determined upon derivatization with Mosher’s acid, absolute configuration have been established by chemical correlation.