Selective benzylic lithiation of N-Boc-2-phenylpiperidine and pyrrolidine: expedient synthesis of a 2,2-disubstituted piperidine NK1 antagonist

Unlike the lithiation of N-Boc-2-alkylpiperidines, which occurs at the 6-position, N-Boc-2-phenylpiperidine and N-Boc-2-phenylpyrrolidine can be lithiated exclusively at the 2-position. The tertiary carbanions can be trapped with a variety of electrophiles. This chemistry was used for the synthesis of a potent NK₁ ligand (K_i = 0.3 nM). The bioactive configuration at the piperidine quaternary center was determined by X-ray analysis to be (S).     

Reaction of sulfene and dichloroketene with open-chain N,N-disubstituted α-aminomethyleneketones. Synthesis of N,N-disubstituted 4-amino-3,4-dihydro-(5-methyl-6-phenyl)(5,6-diphenyl)-1,2-oxathiin 2,2-dioxides and of 4-amino-3-chloro-5-methyl-6-phenyl-2H-pyran-2-ones

Cycloaddition of sulfene to N,N-disubstituted 3-amino-2-methyl-1-phenyl-2-propen-1-ones (I) and 3-amino-1,2-diphenyl-2-propen-1-ones (II) occurred in good to moderate yield only in the case of aliphatic N-substitution to give 4-dialkylamino-3,4-dihydro-(5-methyl-6-phenyl)(5,6-diphenyl)-1,2-oxathiin 2,2-dioxides. Polar 1,4-cycloaddition of dichloroketene to I and II occurred only in the former case, giving in good to moderate yield N,N-disubstituted 4-amino-3,3-dichloro-3,4-dihydro-5-methyl-6-phenyl-2H-pyran-2-ones which were dehydrochlorinated with DBN to N,N-disubstituted 4-amino-3-chloro-5-methyl-6-phenyl-2H-pyran-2-ones. In the reaction of 2-methyl-1-phenyl-3-diphenylamino-2-propen-1-one with dichloroketene, a product was isolated which was proven by uv, ir, nmr and chemical evidence to be the dipolar ion VI, the supposed intermediate of the polar 1,4-cycloaddition of dichloroketene to N,N-disubstituted enaminones.     

Asymmetric Synthesis of 2-Arylindolines and 2,2-Disubstituted Indolines by Kinetic Resolution

Kinetic resolution of 2-arylindolines (2,3-dihydroindoles) was achieved by treatment of their N-tert-butoxycarbonyl (Boc) derivatives with n-butyllithium and sparteine in toluene at −78 °C followed by electrophilic quench. The unreacted starting materials together with the 2,2-disubstituted products could be isolated with high enantiomer ratios. Variable temperature NMR spectroscopy showed that the rate of Boc rotation was fast (ΔG^≠≈57 kJ/mol at 195 K). This was corroborated by DFT studies and by in situ ReactIR spectroscopy. The enantioenriched N-Boc-2-arylindolines were converted to 2,2-disubstituted products without significant loss in enantiopurity. Hence, either enantiomer of the 2,2-disubstituted products could be obtained with high selectivity from the same enantiomer of the chiral ligand sparteine (one from the kinetic resolution and the other from subsequent lithiation-trapping of the recovered starting material). Secondary amine products were prepared by removing the Boc group with acid to provide a way to access highly enantioenriched 2-aryl and 2,2-disubstituted indolines.     

One-pot two-step synthesis of 1-position arylated 1,3-disubstituted isoquinoline N-oxides

A one-pot two-step reaction of 2-alkynylbenzaldoximes with aryl halides has been developed, which offers the 1-position arylated 1,3-disubstituted isoquinoline N-oxides in moderate to good yields in most cases. The isoquinoline N-oxide intermediate was prepared in situ without isolation.     

On the protonation and deuteration of N,N-disubstituted 2-aminothiophenes, 2-aminothiazoles,and some 3-amino substituted analogues

In contrast to their carbocyclic aniline analogues, N,N-diarylsubtituted 2-aminothiophenes are not protonated at their N-atoms but at the 5-position or, to a smaller extent, at the 3-position of the thiophene nucleus giving rise to cationic species of the Wheland type. However, 5-formyl and 5-acetyl-substituted 2-(N,N-diarylamino)thiophenes are protonated at the corresponding carbonyl moieties. This finding not only enables insight into the mechanism of electrophilic substitution of N,N-disubstituted 2-aminothiophenes but also allows to prepare deurated 2-aminothiophenes by treatment their non-deuterated parent compounds with CF₃COOD.     

Reaction of dichloroketene and sulfenc with N,N-disubstituted 2-aminomethylene-1 -indanones. Synthesis of indeno[ 1,2-b ] pyran and lndeno[2,l-e] -1,2-oxathiin derivatives

The 1,4-cycloaddition of dichloroketene to N,N-disubstituted 2-aminomethylcnc-l-indanones afforded N,N-disubstituted 4-ainino-3,3-dichloro-3,4-dihydro-2-oxoindeno[1,2-b ]pyrans only in the case of full or partial aromatic N-substitution. The diphenylamino adduct gave 3-chloro-4-diphenylamino-2-oxoindeno[ 1,2-b]pyran by dehydrochlorination with DBN. The 1,4-cycloaddition with sulfene occurred only in the case of 2-diethylaininomethylene-1-indanone to give 4-diethylamino-3,4-dihydroindeno[2, 1-e]-1,2-oxathiin 2,2-dioxide, a derivative of a new hetero-cyclic system.     

Asymmetric syntheses of methyl N-Boc-2-deoxy-2-amino-l-erythroside,methyl N-Boc-2-deoxy-2-amino-d-threoside and methyl N-Boc-2,3-dideoxy-3-amino-l-arabinopyranoside

The asymmetric syntheses of methyl N-Boc-2-deoxy-2-amino-l-erythroside and methyl N-Boc-2-deoxy-2-amino-d-threoside have been achieved from sorbic acid, in six and eight steps, and in 35 and 13% overall yield, respectively. Diastereoselective aminohydroxylation of tert-butyl sorbate gives access to two diastereoisomeric α-hydroxy-β-amino-γ,δ-unsaturated esters. Reduction of the ester functionality and ozonolysis of the double bond gives the corresponding aldehyde, which exists exclusively in the ring-closed (furanose) form. An alternative synthesis of methyl N-Boc-2-deoxy-2-amino-l-erythroside was also developed, reliant on aminohydroxylation of an α,β-unsaturated ester bearing an acetal functionality at the γ-position, and this synthesis proceeded in five steps and 54% overall yield from acrolein diethyl acetal. This approach was extended to permit the synthesis of methyl N-Boc-2,3-dideoxy-3-amino-l-arabinopyranoside in six steps and 58% overall yield from ethyl 3,3-diethoxypropanote.     

Asymmetric construction of pyrido[1,2-a]-1H-indole derivatives via a gold-catalyzed cycloisomerization

Pyrido[1,2-a]-1H-indoles are important scaffolds found in many biologically active compounds. Herein, we first developed an IPrAuCl/AgSbF₆-catalyzed cycloisomerization of N-1,3-disubstituted allenyl indoles affording pyrido[1,2-a]-1H-indoles. Then the axial-to-central chirality transfer starting from enantio-enriched N-1,3-disubstituted allenylindoles affording optically active pyrido[1,2-a]-1H-indoles has been realized in excellent yields and enantioselectivities. A mechanism has been proposed based on mechanistic studies. Synthetic applications have also been demonstrated.

We reported an IPrAuCl/AgSbF₆-catalyzed cycloisomerization of enantio-enriched N-1,3-disubstituted allenylindoles affording optically active pyrido[1,2-a]-1H-indoles in excellent yields and enantioselectivities.     

Reaction of sulfene and dichloroketene with open-chain N,N-disubstituted α-aminomethyleneketones. Synthesis of 4-dialkylamino-3,4-dihydro-5,6-dimethyl-1,2-oxathiin 2,2-dioxides and of 6,(5)(di)alkyl-3-chloro-4-methylphenylamino-2H-pyran-2-ones

Cycloaddition of sulfene to N,N-disubstituted 4-amino-3-methyl-3-buten-2-ones (III) occurred in fair to good yield only in the case of aliphatic N-substitution to give 4-dialkylamino-3,4-dihydro-5,6-dimethyl-1,2-oxathiin 2,2-dioxides, whereas N,N-disubstituted 1-amino-1-penten-3-ones (II) did not react at all. Cycloaddition of dichloroketene to II, III and N,N-disubstituted 4-amino-3-buten-2-ones occurred only in the case of the methylphenylamino derivative, giving in good to moderate yield 6,(5)(di)alkyl-3,3-dichloro-3,4-dihydro-4-methylphenylamino-2-Hpyran-2-ones, which were dehydrochlorinated with DBN to 6,(5)(di)alkyl-3-chloro-4-methylphenylamino-2H-pyran-2-ones.     

Multisubstituted N-fused heterocycles via transition metal-catalyzed cycloisomerization protocols

Two complementary protocols for assembly of multisubstituted N-fused heterocycles have been developed. It was demonstrated that 1,3-disubstituted N-fused heterocycles, including indolizines, pyrroloquinoxalines, and pyrrolothiazoles can easily be synthesized via an exceptionally mild and efficient method involving a novel silver-catalyzed cycloizomerization of propargyl-containing heterocycles. Alternatively, 1,2-disubstituted heterocycles can be accessed through the novel cascade transformation involving an alkyne-vinylidene isomerization with concomitant 1,2-shift of hydrogen, silyl, stannyl, or germyl groups. This mild and simple method allows for selective and highly efficient synthesis of indolizines, pyrroloisoquinolines, pyrroloquinoxalines, pyrrolopyrazines, and pyrrolothiazoles.     

Reaction of ketenes with N,N-disubstituted α-aminomethyleneketones. XVIII. Synthesis of N,N-disubstituted 4-amino-3-phenyl-2H-naphtho[1,2-b]pyran-2-ones

1,4-Cycloaddition of phenylchloroketene to N,N-disubstituted 2-aminomethylene-3,4-dihydro-1(2H)naphthalenones gave the corresponding adducts, namely N,N-disubstituted 4-amino-3-chloro-3,4,5,6-tetrahydro-3-phenyl-2H-naphtho[1,2-b]pyran-2-ones II, in the case of aliphatic N,N-disubstitution or aromatic N-monosubstitution. Apart from IIf (NR₂ = NMePh), adducts II were unstable and were dehydrochlorinated in situ with DBN to give N,N-disubstituted 4-amino-5,6-dihydro-3-phenyl-2H-naphtho[1,2-b]pyran-2-ones III in fair overall yields. Compounds III were dehydrogenated with Pd/C in boiling p-cymene to afford the title compounds generally in high yields.     

Synthesis and Antimicrobial Activity of N,N-Disubstituted 3-Allyloxy-1-amino-2-propanethiols

3-Allyloxy-1,2-epithiopropane was synthesized; its treatment with amines yielded N,N-disubstituted 3-allyloxy-1-amino-2-propanethiols, which were tested for antimicrobial activity.     

Adamantylazoles: XIV. Acid-catalyzed alkylation of 5-aminotetrazoles with tertiary alcohols

Alkylation of 5-aminotetrazole with tert-butyl alcohol or adamantan-1-ol in sulfuric acid gave a mixture of isomeric N ¹- and N ²-alkyl derivatives, as well as 1,3-dialkyl-5-aminotetrazolium salt. Adamantylation of 1-substituted 5-aminotetrazoles led to the formation of mixtures of 1,3- and 1,4-disubstituted 5-aminotetrazolium salts which can be converted into the corresponding free bases.     

Reactions of 1,2,4-triazole derivatives with a “model” thiirane

Reactions of 3-mono- and 3,5-disubstituted 1,2,4-triazoles with a “model” thiirane, 8-bromo-1,3-dimethyl-7-(thiiran-2-ylmethyl)-3,7-dihydro-1H-purine-2,6-diones proceed at the positions N¹ and N² of the triazole ring and yield 7-(5-R-3-R′-1,2,4-triazol-1-yl)methyl- and/or 7-(5-R′-3-R-1,2,4-triazol-1-yl)methyl-1,3-dimethyl-6,7-dihydro[1,3]thiazolo[2,3-f]-purine-2,4-(1H,3H)-diones. 3-Methylsulfonyl-1,2,4-triazole reacted regiospecifically at the position N¹ forming 1,3-dimethyl-7-[(3-methyl-sulfonyl-1,2,4-triazole-1-yl)-methyl]-6,7-dihydro[1,3]thiazolo-[2,3-f]purine-2,4(1H,3H)-dione.     

Facile One-Step Oxidation of N-Boc-Protected Diarylhydrazines to Diaryldiazenes with (Diacetoxyiodo)benzene under Mild Conditions

A study on the oxidation of N-Boc- and N,N'-bis-Boc-protected 1,2-diarylhydrazines with (diacetoxyiodo)benzene is reported. The reactions proceed quickly in acetic acid at slightly elevated temperatures, giving diaryldiazenes in good to excellent yields. Electron-donating and electron-withdrawing groups are well tolerated. This synthetic protocol also applies to synthesising (aryldiazenyl)pyridines and unsymmetrical 1,3,5-tris(arylazo)benzenes.     

Reaction of sulfene with heterocyclic N,N-disubstituted α-aminomethyleneketones. XI. Synthesis of 1,2-oxathiino[5,6-d]-1-benzoxepin derivatives

The 1,4-cycloaddition of sulfene to N,N-disubstituted (E)-4-aminomethylene-3,4-dihydro-1-benzoxepin-5(2H)-ones gave, generally in excellent yield, N,N-disubstituted 4-amino-3,4,5,6-tetrahydro-1,2-oxathiino-[5,6-d)-1-benzoxepin 2,2-dioxides, which are derivatives of the new heterocyclic system 1,2-oxathiino[5,6-d]-1-benzoxepin. This reaction did not occur only with the N,N-diphenylenaminone.     

An efficient procedure for the synthesis of 2-N-Boc-amino-3,5-diols

We wish to describe here the diastereoselective reaction between chiral N-Boc-α-amino aldehydes with both achiral allyltrichlorostannanes leading to 1,2-syn-N-Boc-α-amino alcohols, which are easily converted to the corresponding 4-N-Boc-amino-3-hydroxy ketones after treatment with catalytic amounts of OsO₄ in the presence of NaIO₄. After reduction of the carbonyl function, these 4-N-Boc-amino-3-hydroxy ketones were converted to 1-deoxy-5-hydroxy sphingosine analogues.     

Electrophilic Reactivities of 1,2‐Diaza‐1,3‐dienes

The kinetics of the reactions of 1,2‐diaza‐1,3‐dienes 1 with acceptor‐substituted carbanions 2 have been studied at 20 °C. The reactions follow a second‐order rate law, and can be described by the linear free energy relationship log k(20 °C)=s(N+E) [Eq. (1)]. With Equation (1) and the known nucleophile‐specific parameters N and s for the carbanions, the electrophilicity parameters E of the 1,2‐diaza‐1,3‐dienes 1 were determined. With E parameters in the range of ?13.3 to ?15.4, the electrophilic reactivities of 1 a–d are comparable to those of benzylidenemalononitriles, 2‐benzylideneindan‐1,3‐diones, and benzylidenebarbituric acids. The experimental second‐order rate constants for the reactions of 1 a – d with amines 3 and triarylphosphines 4 agreed with those calculated from E, N, and s, indicating the applicability of the linear free energy relationship [Eq. (1)] for predicting potential nucleophilic reaction partners of 1,2‐diaza‐1,3‐dienes 1 . Enamines 5 react up to 10² to 10³ times faster with compounds 1 than predicted by Equation (1), indicating a change of mechanism, which becomes obvious in the reactions of 1 with enol ethers.     

Reaction of substituted sulfenes with N,N-disubstituted α-amino-methyleneketones. II. Synthesis of N,N-disubstituted cis and trans 4-amino-3-chloro-3,4,5,6,7,8-hexahydro-1,2-benzoxathiin 2,2-dioxides,and 4-amino-5,6,7,8-tetrahydro-1,2-benzoxathiin 2,2-dioxides

The polar 1,4-cycloaddition of chlorosulfene (generated in situ from chloromethanesulfonyl chloride and triethylamine) to N,N-disubstituted (E)-2-aminomethylenecyclohexanones I gave mixtures of N,N-disubstituted cis and trans 4-amino-3-chloro-3,4,5,6,7,8-hexahydro-1,2-benzoxathiin 2,2-dioxides III and IV, except for N,N-diphenyl enaminone which did not react. Only compounds IV could be separated from these mixtures by silica gel chromatography, with the exception of the piperidino adducts (III + IV)d, from which also IIId could be obtained pure. Compounds IV or mixtures III + IV were dehydrochlorinated with DBN in refluxing benzene to afford N,N-disubstituted 4-amino-5,6,7,8-tetrahydro-1,2-benzoxathiin 2,2-dioxides V in satisfactory yields. Structural and conformational features of compounds III, IV and V were determined from uv, ir and nmr spectral data.     

Reaction of sulfene with heterocyclic N,N-disubstituted α-aminomethvlene ketones V. Synthesis of 1,2-oxatliiino[5.6-c] pyridine and 1,2-oxathiino[5,6-c] quinoline derivatives

Reaction of sulfene with N,N-disubstituted 3-aminomethylene-1-(methyl, methylphenyl, phenyl)-4-piprridones and 3-aminomethylene-2,3-dihydro-1-plumy 1–4(1H) quinolones gave N,N-disubstituted 4-amino-3,4,5,6,7.8-hexahydro-6-(methyl, methylphenyl, phenyl)-1,2-oxathiino-[5,6-c] pyridine 2,2-dioxides and 4-amino-6-phenyl-3,4,5,6-tetrahydro-1,2-oxathiino[5,6-c]quinoline 2,2-dioxides, respectively, whereas N,N-disubstituted 3-aminomethylene-2,3-dihydro-1-methyl-4(1H) quinolones did not react. Slow air oxidation in the cold of intermediates 2,3-dihydro-3-hydroymethyIene-1-(methyl, phenyl)-4(1H) quinolones gave the corresponding 1-substituted 1,4-dihydro-4-oxo-3-quinolinecarboxyaldehydes.