Enantiocomplementary inverting sec-alkylsulfatase activity in cyano- and thio-bacteria Synechococcus and Paracoccus spp.: selectivity enhancement by medium engineering

Whole resting cells of cyano- and thio-bacteria Synechococcus and Paracoccus spp. were shown to possess inverting alkylsulfatase activity for a broad spectrum of sec-alkylsulfate esters, which furnished either (R)- or (S)-sec-alcohols from the corresponding rac-sulfate esters in an enantiocomplementary fashion. Low enantioselectivities (E-values 1–4) could be dramatically improved by the addition of lower alcohols (e.g., t-BuOH) or by using a biphasic medium containing t-BuOMe (E >200).     

A two-step synthesis of aminopropylpiperidines via aminopropargylpyridines, suitable for the synthesis of a new class of 5-HT4 ligands

A rapid and flexible synthetic approach to {[bis(tert-butoxycarbonyl)amino]propyl}piperidines 5 and related compounds is described. The key step is a three-component coupling process of 2-, 3- or 4-bromopyridine, propargyl bromide and potassium di-tert-butyliminodicarbonate under palladium-copper catalysis leading to 2-, 3- or 4-{[bis(tert-butoxycarbonyl)amino]-propargyl}pyridines 4 followed by a catalytic reduction step.     

Base dependent purported synthesis of congested 2-aminobenzylamines and tetrahydro-2-oxoquinazolines from 2-pyranones

An expeditious and concise synthesis of highly congested 2-amino-3-aminomethyl-5-methylsulfanyl/-sec-aminobiphenyl-4-carbonitrile 4 and 1-tert-butoxycarbonyl-6-sec-amino-8-aryl-5-cyano-2-oxo-1,2,3,4-tetrahydroquinazoline 5 has been delineated through base catalyzed ring transformation of 6-aryl-4-methylsulfanyl/-sec-amino-2H-pyran-2-one-3-carbonitrile 1 with 1,3-bis(tert-butoxycarbonylamino)-2-propanone 2, followed by TFA catalyzed hydrolysis of the intermediate [3-tert-butoxycarbonylaminomethyl-4-cyano-5-methylsulfanyl/-sec-aminobiphenyl-2-yl]carbamic acid tert-butyl ester 3 in moderate yield. The mechanism of formation of 5 has been established through isolation and transformation of the intermediate 3 to the 1-tert-butoxycarbonyl-6-sec-amino-8-aryl-5-cyano-2-oxo-1,2,3,4-tetrahydroquinazoline.     

Versatile method for introduction of bulky substituents to alkoxychlorosilanes

The reactions of various alkoxytrichlorosilanes prepared in situ from tetrachlorosilane and alcohols, with Grignard reagents bearing a bulky substituent such as the isopropyl, sec-butyl, and cyclohexyl group afforded triisopropyl-, tri(sec-butyl)-, and tricyclohexylalkoxysilane in high yields. The reactions of n-butoxytrichlorosilane with these Grignard reagents produced triisopropyl-, tri(sec-butyl)-, and tricyclohexyl(n-butoxy)silane in 94%, 96%, and 92% yields, respectively. Methoxymethyldichlorosilane reacted with the same Grignard reagents to give diisopropyl-, di(sec-butyl)-, and dicyclohexylmethoxymethylsilane in 84%, 83%, and 83% yields. Treatment of methoxydimethylchlorosilane with the Grignard reagents readily afforded isopropyl-, sec-butyl-, and cyclohexylmethoxydimethylsilane in excellent yields. Similar treatment of methoxydimethylchlorosilane with tert-butylmagnesium chloride gave tert-butylmethoxydimethylsilane in 62% yield.     

(Vapor + liquid) equilibria of the binary mixtures of m-cresol with C1-C4 aliphatic alcohols at 95.5 kPa

Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures formed by m-cresol with: methanol, ethanol, 1-propanol, 2-propanol, and n-, iso-, sec-, and tert-butanols - using a Swietoslawski-type ebulliometer. The liquid phase composition - bubble point temperature measurements are well represented by the Wilson model. (Vapor + liquid) equilibria predicted from the model are presented.     

Bubble point temperatures of the binary mixtures of nitrobenzene with C1–C4 aliphatic alcohols at 94.95 kPa

Bubble point temperatures at 94.95 kPa, over the entire composition range, are measured for the binary mixtures of nitrobenzene with: methanol, ethanol, 1-propanol, 2-propanol and n-, iso-, sec- and tert-butanols – using a Swietoslawski-type ebulliometer. The liquid phase composition – bubble point temperature measurements are well represented by the Wilson model.     

Reactivity of 1-phenylsulfinyl-2-phenylsulfanylethylene (SOSE) with O-nucleophiles generated by potassium tert-butoxide

E-1-Phenylsulfinyl-2-phenylsulfanylethylene (E-SOSE) reacts with O-nucleophiles generated by means of t-BuOK via an addition-elimination mechanism, thus affording the product of substitution of the phenylsulfanyl group in a stereo-conservative process. When used alone, the strongly basic and hindered tert-butoxide brings about elimination of either the phenylthiolate or phenylsulfinate groups. Z-SOSE is much more prone to elimination: either with t-BuOK alone or with other O-nucleophiles generated by t-BuOK, it always leads to products derived from elimination. Other alkaline tert-butoxides or other bases appear not as effective in generating species nucleophilic enough to react with E-SOSE.     

Synthesis of novel fused azecine ring systems through application of the tert-amino effect

Novel fused azecine ring systems were synthesized via the microwave-assisted thermal isomerization of terphenyl or biphenyl-pyridazine compounds possessing a vinyl and a tert-amino group, through application of a new extension of the tert-amino effect. Substrates for the ring closure were prepared from ortho-dihalobenzene or pyridazinone by consecutive Suzuki couplings with ortho-sec-amino- and formylphenylboronic acids, followed by Knoevenagel condensation of the aldehydes obtained.     

Reaction between tert-butyl isocyanide, dialkyl acetylenedicarboxylates, and aromatic carboxylic acids: an efficient method for the synthesis of dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dialkyl acetylenedicarboxylates by aromatic carboxylic acids leads to vinylnitrilium cations, which undergo nucleophilic reaction with conjugate bases of the carboxylic acids to produce dialkyl (E)-2-[(benzoyloxy)(tert-butylimino)methyl]-2-butenedioates and this intermediate rearranges to the dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives.     

Synthesis of stable 1-ethoxy-2,3-diferrocenylcyclopropenylium tetrafluoroborate and its reactions with lithium reagents

1-Ethoxy-2,3-diferrocenylcyclopropenylium tetrafluoroborate selectively reacts with MeLi, n-BuLi, sec-BuLi with formation of the 3,3-dialkyl-1,2-diferrocenylcyclopropenes, while with tert-BuLi both 2-tert-butyl-1,3-diferrocenylcyclopropene and 1,3-di-tert-butyl-2,3-diferrocenylcyclopropene are obtained. The structures of 3,3-dimethyl-, 3,3-dibutyl-1,2-diferrocenyl and 2-tert-butyl-1,3-diferrocenylcyclopropenes were confirmed by X-ray crystallographic analysis.     

Synthesis of new α-aminophosphonates containing sterically hindered phenol fragments based on the reaction of 3,5-di(tert-butyl)-4-oxo-2,5-cyclohexadienylidenemethylphosphonates with aliphatic amines

A reaction of aliphatic amines (n-butylamine, sec-butylamine, tert-butylamine, dodecylamine, 1,12-diaminododecane) with α-phosphorylated methylenequinones (dimethyl {[3,5-di-(tert-butyl)-4-oxo-2,5-cyclohexadienylidene]methyl}phosphonate and diphenyl {[3,5-di(tertbutyl)-4-oxo-2,5-cyclohexadienylidene]methyl}phosphonate)) to form 1,6-nucleophilic addition products was studied. This approach was used to obtain a-aminophosphonates containing sterically hindered phenol fragments in high yields.     

A novel route for the synthesis of highly congested aryl-tethered 2-aminobenzylamines through ring transformation of 2-pyranones

An innovative and efficient synthesis of highly congested 2-amino-3-aminomethyl-5-methylsulfanyl/sec-aminobiphenyl-4-carbonitriles 4 has been delineated through base catalyzed ring transformation of 6-aryl-4-methylsulfanyl/sec-amino-2H-pyran-2-one-3-carbonitriles 1 with Boc-protected 1,3-diamino-2-propanone 2, followed by TFA catalyzed hydrolysis of the intermediate [3-tert-butoxycarbonylaminomethyl-4-cyano-5-methylsulfanyl/sec-aminobiphenyl-2-yl]carbamic acid tert-butyl ester 3 in moderate yields as the TFA salts.     

Highly diastereoselective synthesis of α-trifluoromethylated α-propargylamines by acetylide addition to chiral CF3-substituted N-tert-butanesulfinyl ketimines

A convenient and practical method for the preparation of enantiomerically pure α-trifluoromethylated α-propargylamines is described. A range of enantiopure α-trifluoromethylated α-propargyl sulfinamides were obtained by the addition of lithium acetylides generated in situ with n-BuLi and terminal alkynes to diverse chiral CF₃-substituted (S)-N-tert-butanesulfinyl ketimines in moderate to excellent yields (56–97%) and with uniformly excellent diastereoselectivities (>99:1) by using Ti(OⁱPr)₄ as the catalyst and THF as the polar solvent. Enantiomerically pure α-trifluoromethylated α,α-dibranched propargyl amines were then readily obtained in excellent yields (87–97%) by acidic cleavage of the tert-butanesulfinyl group.     

Asymmetric synthesis of 4-amino-γ-butyrolactones via lithium amide conjugate addition

Upon treatment with homochiral lithium (R)-N-benzyl-N-(α-methylbenzyl)amide, γ-benzyloxy but-2-enoates undergo competitive conjugate addition and γ-deprotonation, while γ-tert-butyldimethylsilyloxy but-2-enoates undergo exclusive conjugate addition. Treatment of γ-benzyloxy or γ-tert-butyldimethylsilyloxy but-2-enamides with lithium (R)-N-benzyl-N-(α-methylbenzyl)amide furnishes exclusively the γ-benzyloxy- or γ-tert-butyldimethylsilyloxy-β-amino amide products of conjugate addition in high de. The γ-tert-butyldimethylsilyloxy-β-amino butanoate products of conjugate addition readily undergo O-desilylation and concomitant cyclisation to furnish 4-[N-benzyl-N-(α-methylbenzyl)amino]-γ-butyrolactone, which may be stereoselectively functionalised via deprotonation and alkylation to give the corresponding trans-3-alkyl-4-amino-γ-butyrolactones. Alternatively, stereoselective alkylation of γ-benzyloxy- or γ-tert-butyldimethylsilyloxy-β-amino butanoates and butanamides through enolate formation and alkylation following a tandem (via the (Z)-lithium enolate) or stepwise (via the (E)-lithium enolate) protocol gives a range of separable syn- and anti-α-alkyl-β-amino esters and amides. O-Silyl deprotection of the syn- and anti-α-alkyl-β-amino butanoates with TBAF and concomitant cyclisation provide trans-3-alkyl-4-amino-γ-butyrolactones, consistent with epimerisation to the thermodynamically favoured trans-lactone occurring upon deprotection.     

Crown ether-tert-ammonium salt complex fixed as rotaxane and its derivation to nonionic rotaxane

First rotaxane having tert-ammonium axle was prepared from tert-ammonium salt axle and dibenzo-24-crown-8-ether (DB24C8) wheel, suggesting that tert-ammonium salt axle forms the corresponding threaded complex with a crown ether. Same rotaxane was obtained quantitatively by N-methylation of sec-ammonium-type rotaxane. The tert-ammonium-type rotaxane was neutralized with amine base to tert-amine-type rotaxane in 100% yield, indicating the first isolation of ‘nonionic’ amine-type rotaxane. The reversible protonation and deprotonation of tert-amine-type rotaxane were achieved.     

Excess Gibbs free energies of the binary mixtures of acetonitrile with butanols at 94.83 kPa

Bubble point temperatures at 94.83 kPa, over the entire composition range, are measured for the binary mixtures of acetonitrile with: n-, iso-, sec- and tert-butanols – using a Swietoslawski type ebulliometer. The liquid phase composition versus bubble point temperature measurements are found to be well represented by the Wilson model. Measured values of the liquid phase mole fraction versus bubble point temperature data are presented along with the computed values of the vapor phase mole fractions, activity coefficients and excess Gibbs free energies and discussed.     

Enantioselective α-hydroxylation of β-keto esters catalyzed by chiral S-timolol derivatives

A screen of aryloxy aminopropanol organocatalysts derived from the β-blocker inhibitor S-timolol determined the most active catalyst of asymmetric α-hydroxylation of β-keto esters. (R)-1-(tert-butylamino)-3-(3,4,5-trimethoxyphenoxy) propan-2-ol (3k) was the most effective derivative, enantioselectively catalyzing α-hydroxylation of β-keto esters using tert-butyl hydroperoxide as the oxidant in hexane to afford the corresponding products in excellent yield and with good enantioselectivity (up to 96% yield, 88% ee).     

1,5-Stereocontrol in reactions of 2,4-disubstituted alk-2-enylstannanes with aldehydes; an approach to the stereoselective synthesis of branched triols

2-(tert-Butyldimethylsilyloxymethyl)-4-(methoxymethoxy)pent-2-enyl(tributyl)stannane is transmetallated by tin(IV) chloride stereoselectively to give a pent-1-en-3-yltin trichloride that reacts with aldehydes with excellent (E)-1,5-syn-stereocontrol, e.g. (3E)-1,5-syn-3-(tert-butyldimethylsilyloxymethyl)-5-(methoxymethoxy)-1-phenylhex-3-en-1-ol was the dominant product with benzaldehyde. The products from these reactions were taken through to more complex 2-substituted alk-2-enyl(tributyl)stannanes but only very low yields of the expected products were obtained from tin(IV) chloride mediated reactions of these stannanes and aldehydes. Nevertheless a stereoselective synthesis of 2-substituted 4-[(E)-2-alkoxypropylidene]tetrahydrofurans was developed.     

Selective mono-acylation of 1,2- and 1,3-diols using (α,α-difluoroalkyl)amines

In the reaction of N,N-diethyl-α,α-difluorobenzylamine (DFBA) with 1,2- or 1,3-diols, selective mono-benzoylation occurs to afford mono-esters of the diols in good yield. The reaction is completed under mild conditions in a short reaction time. Further, prim-, sec-, and tert-diols and catechol can be converted to the corresponding mono-benzoates. DFBA is used for the protection of the hydroxy group in sugars. The selective mono-nicotinylation, formylation and pivaloylation of diols are also performed by using the corresponding difluoroalkylamines.     

Synthesis of macrocyclic precursors of lankacidins using Stille reactions of 4-(2-iodo-alkenyl)azetidinones and related compounds for ring closure

In the context of a proposed total synthesis of lankacidins, the synthesis of 4-(2-iodo-alkenyl)azetidinones and their participation in Stille coupling reactions have been investigated. 1-tert-Butyldimethylsilyl-4-(2-iodoethenyl)azetidinone was found to undergo a Stille coupling reaction with a 3-hydroxy-1-tributylstannylhepta-1,5-diene to give an acceptable yield of the corresponding conjugated diene but the analogous reaction with a 3-tert-butyldimethylsilyloxy-1-tributylstannylhepta-1,5-diene was unsuccessful. A series of 4-[(E)-2-iodoprop-1-enyl]azetidinones, a ring-opened ester and a lactone were also found to undergo Stille reactions with 3-tributylstannylprop-2-enol albeit with variable yields. Asymmetric syntheses of methyl (2R,3R,5S)-3-tert-butyldimethylsilyloxy-2-methyl-5-(2-trimethylsilylethoxy)methoxy-6-oxohexanoate, (3R,4S)-1-tert-butyldimethylsilyl-4-[(E)-2-iodoprop-1-enyl]-3-methylazetidin-2-one, and (5S,2E,6E)-5-tert-butyldimethylsilyloxy-2-methyl-1-phenylsulfonyl-7-tributylstannylhepta-2,6-diene and their incorporation into macrocyclic precursors of the lankacidins were then investigated. Key reactions were a Julia reaction between the aldehyde and the sulfone to form the 12,13-double-bond, a stereoselective acylation of the azetidinone, and formation of macrocycles using intramolecular Stille reactions in the presence of a free hydroxyl group at C(8) (lankacidin numbering).