Nucleophilic reactivity of 1-zirconacyclopent-3-ynes: Carbon-carbon bond formation with aldehydes

Nucleophilic reactions of 1,1-bis(η⁵-cyclopentadienyl)-1-zirconacyclopent-3-yne (1) with proton and aldehydes were studied. The reaction with HCl gave a mixture of 2-butyne and 1,2-butadiene. Complex 1 reacted with benzaldehyde to give 1-phenyl-2-methyl-2,3-butadien-1-ol (3) in moderate yields in the presence of a proton source such as triethylammonium hydrochloride, while it gave 2-methylene-1-phenyl-3-buten-1-ol (4) on using triethylammonium tetraphenylborate.     

Preparation of 1,1-disubstituted silacyclopentadienes

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.     

Studies on the mechanism for stereoisomerization of 1-zirconacyclopent-3-yne compounds

The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η⁵-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d₆ solution were observed using ¹H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (k_H/k_D = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η⁴-π,π-coordination mode is proposed.     

Studies on the mechanism for stereoisomerization of 1-zirconacyclopent-3-yne compounds

The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η⁵-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d₆ solution were observed using ¹H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (k_H/k_D = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η⁴-π,π-coordination mode is proposed.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Synthesis and preliminary cytotoxicity studies of achiral pyrrolyl-substituted titanocenes

From the reaction of various 6-pyrrolylfulvenes (3a–3d) with Super Hydride (LiBEt₃H), lithiated cyclopentadienide intermediates (4a–4d) were synthesised. These intermediates were then transmetallated with titanium tetrachloride TiCl₄ to yield the pyrrolyl-substituted titanocenes bis-[((1-(4-methoxybenzyl)-pyrrole)2-)cyclopentadienyl]titanium(IV) dichloride (5a), bis-[((1-(4-methoxyphenyl)-pyrrole)2-)cyclopentadienyl]titanium(IV) dichloride (5b), bis-[((2,4-bis(4-methoxyphenyl)-1-methyl-pyrrole)2-)cyclopentadienyl]titanium(IV) dichloride (5c), bis-[((2-(4-methoxyphenyl)-1-methyl-pyrrole)2-)cyclopentadienyl]titanium(IV) dichloride (5d). Titanocene 5b crystallised and was characterised by X-ray crystallography. The four titanocenes 5a–5d were tested for their cytotoxicity through MTT-based in vitro tests on CAKI-1 cell lines in order to determine their IC₅₀ values. Titanocenes 5a–5d were found to have IC₅₀ values of 440 (±35), 68 (±14), 105 (±30), and 36 (±7) μM.     

Novel design of 3,8-diazabicyclo[3.2.1]octane framework in oxidative sulfonamidation of 1,5-hexadiene

1,5-Hexadiene reacts with trifluoromethanesulfonamide in the oxidative system (t-BuOCl+NaI) to give trans-2,5-bis(iodomethyl)-1-(trifluoromethylsulfonyl)pyrrolidine 5 and 3,8-bis(trifluoromethylsulfonyl)-3,8-diazabicyclo[3.2.1]octane 6. With arenesulfonamides ArSO₂NH₂ (Ar=Ph, Tol), the reaction stops at the formation of the trans and cis isomers of 2,5-bis(iodomethyl)-1-(arenesulfonyl)pyrrolidine 7 and 8 (1:1). The cis isomers of 7 and 8 do not undergo cyclization to the corresponding 3,8-disubstituted 3,8-diazabicyclo[3.2.1]octanes. The reaction with triflamide represents the first example of one-pot two-step route to 3,8-diazabicyclo[3.2.1]octane system.     

Reaction of azulene with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol in a mixed solvent of methanol and acetonitrile in the presence of hydrochloric acid: a facile one-pot synthesis and properties of new triarylethylenes possessing an azulen-1-yl group

Reaction of azulene (1) with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol (2) in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives 2-(azulen-1-yl)-1,1-bis[4-(dimethylamino)phenyl]ethylene (3) (8% yield), 1-(azulen-1-yl)-(E)-1,2-bis[4-(dimethylamino)phenyl]ethylene (4) (28% yield), and 1,3-bis{2,2-bis[4-(dimethylamino)phenyl]ethenyl}azulene (5) (9% yield). Besides the above products, this reaction affords 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethane (6) (15% yield), a meso form (1R,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethane (7) (6% yield), and the two enantiomeric forms (1R,2R)- and (1S,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethanes (8) (6% yield). Furthermore, addition reaction of 3 with 1 under the same reaction conditions as the above provides 6, in 46% yield, which upon oxidation with DDQ (=2,3-dichloro-5,6-dicyano-1,4-benzoquinone) in dichloromethane at 25 °C for 24 h yields 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethylene (9) in 48% yield. Interestingly, reaction of 1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene (11) with 1 in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives guaiazulene (10) and 3, owing to the replacement of a guaiazulen-3-yl group by an azulen-1-yl group, in 91 and 46% yields together with 5 (19% yield) and 6 (13% yield). Similarly, reactions of 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (12) and 1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}-2-(3-guaiazulenyl)ethylene (13) with 1 under the same reaction conditions as the above provide 10, 2-(azulen-1-yl)-1,1-bis(4-methoxyphenyl)ethylene (16), and 1,3-bis[2,2-bis(4-methoxyphenyl)ethenyl]azulene (17) (93, 34, and 19% yields) from 12 and 10 and 2-(azulen-1-yl)-1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}ethylene (18) (97 and 58% yields) from 13.     

Synthesis and cytotoxicity studies of methoxy benzyl substituted titanocenes

From the reaction of 6(2-methoxy-phenyl)fulvene (1a), 6(3-methoxy-phenyl)fulvene (1b), 6(3,4-dimethoxy-phenyl)fulvene (1c) and 6(3,4,5-trimethoxy-phenyl)fulvene (1d) with LiBEt₃H, lithiated cyclopentadienide intermediates 2a-d were synthesised. These intermediates were then transmetallated to titanium with TiCl₄ to give benzyl substituted titanocenes bis-[(2-methoxy-benzyl)cyclopentadienyl]titanium(IV) dichloride (3a), bis-[(3-methoxy-benzyl)cyclopentadienyl]titanium(IV) dichloride (3b), bis-[(3,4-dimethoxy-benzyl)cyclopentadienyl]titanium(IV) dichloride (3c) and bis-[(3,4,5-trimethoxy-benzyl)cyclopentadienyl]titanium(IV) dichloride (3d). The three titanocenes 3a-c were characterised by single crystal X-ray diffraction, while the structure of the fourth titanocene 3d was elucidated through a DFT calculation. All four titanocenes had their cytotoxicity investigated through preliminary in vitro testing on the LLC-PK (pig kidney epithelial) cell line in order to determine their IC₅₀ values. Titanocenes 3a-d were found to have IC₅₀ values of 97, 159, 88 and 253 μM, respectively. All four titanocene derivatives show significant cytotoxicity improvement when compared to unsubstituted titanocene dichloride.     

Novel titanocene anti-cancer drugs derived from fulvenes and titanium dichloride

Starting from 6-(p−N,N-dimethylanilinyl)fulvene (1a) or 6-(pentamethylphenyl)fulvene (1b) [1,2-di(cyclopentadienyl)-1,2-di(p−N,N-dimethylaminophenyl)ethanediyl] titanium dichloride (2a) and [1,2-di(cyclopentadienyl)-1,2-bis(pentamethylphenyl)ethanediyl] titanium dichloride (2b) and their corresponding dithiocyanato complexes (3a, 3b) were synthesized. Titanocene 2b did not show a cytotoxic effect, but when 2a was tested against pig kidney carcinoma cells (LLC-PK) or human ovarian carcinoma cells (A2780/cp70) inhibitory concentrations (IC₅₀) of 2.7 × 10⁻⁴ and 1.9 ×  10⁻⁴ M, respectively, were observed.     

Rh(II)-Catalyzed asymmetric carbene transfer with ethyl 3,3,3-trifluoro-2-diazopropionate

The asymmetric cyclopropanation of 1,1-diphenylethylene (2) with ethyl 3,3,3-trifluoro-2-diazopropionate (1) in the presence of chiral Rh(II) catalysts affords cyclopropane 3 with yields and enantioselectivities of up to 72 and 40%, respectively. Similar results are obtained for asymmetric cyclopropenation of hex-1-yne (4), although enantioselectivity is lower. The cyclopropanation of mono-substituted olefins (8a-8e) with 1 leads to cis/trans-mixtures of cyclopropanes 9a-9e with a maximum ee of 75% for 4-methoxystyrene (8c).     

Reactions of azulenes with 1,2-diaryl-1,2-ethanediols in methanol in the presence of hydrochloric acid: comparative studies on products, crystal structures, and spectroscopic and electrochemical properties

Although reaction of guaiazulene (1a) with 1,2-diphenyl-1,2-ethanediol (2a) in methanol in the presence of hydrochloric acid at 60 °C for 3 h under aerobic conditions gives no product, reaction of 1a with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol (2b) under the same reaction conditions as 2a gives a new ethylene derivative, 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (3), in 97% yield. Similarly, reaction of methyl azulene-1-carboxylate (1b) with 2b under the same reaction conditions as 1a gives no product; however, reactions of 1-chloroazulene (1c) and the parent azulene (1d) with 2b under the same reaction conditions as 1a give 2-[3-(1-chloroazulenyl)]-1,1-bis(4-methoxyphenyl)ethylene (4) (81% yield) and 2-azulenyl-1,1-bis(4-methoxyphenyl)ethylene (5) (15% yield), respectively. Along with the above reactions, reactions of 1a with 1,2-bis(4-hydroxyphenyl)-1,2-ethanediol (2c) and 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol (2d) under the same reaction conditions as 2b give 2-(3-guaiazulenyl)-1,1-bis(4-hydroxyphenyl)ethylene (6) (73% yield) and (Z)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1-phenylethylene (7) (17% yield), respectively. Comparative studies of the above reaction products and their yields, crystal structures, spectroscopic and electrochemical properties are reported and, further, a plausible reaction pathway for the formation of the products 3-7 is described.     

A facile synthesis of 3 or 3,3′-substituted binaphthols and their applications in the asymmetric addition of diethylzinc to aldehydes

By using a direct ortho-lithiation, the ligands (S)-3-methoxymethyl-1,1′-bi-2-naphthol [(S)-1], (S)-3,3′-bis(methoxymethyl)-1,1′-bi-2-naphthol [(S)-2], (S)-3-(quinolin-2-yl)-1,1′-bi-2-naphthol [(S)-3] and (S)-3,3′-bis(quinolin-2-yl)-1,1′-bi-2-naphthol [(S)-4] have been synthesized. (S)-1 and (S)-3 show moderate catalytic properties for the asymmetric diethylzinc addition to aromatic aldehydes.     

Chiral cyclopentadienyl ruthenium(II) complexes with P,P-ligands derived from (1R,2R)-1,2-diaminocyclohexane: Synthesis,crystal structures and catalytic activity in Diels–Alder reactions

Chiral cyclopentadienyl ruthenium(II) complexes [CpRu(L1–L3)Cl] (5–7) have been prepared by reaction of [CpRu(PPh₃)₂Cl] with chiral P,P-ligands (1R,2R)-1,2-bis(diphenylphosphinamino)cyclohexane (L1), N,N′-[bis-(3,3′-bis-tert-butyl-5,5′-bis-methoxy-1,1′-biphenyl-2,2′-diyl)phosphite]-(1R,2R)-1,2-diaminocyclohexane (L2) and N,N′-[bis-(R)-1,1′-binaphtyl-2,2′-diyl)phosphite]-(1R,2R)-1,2-diaminocyclohexane (L3). The molecular structures of 5 and 6 have been determined by single-crystal X-ray analysis. Studies on catalytic activity of the cations derived from (5–7) by treatment with AgSbF₆, are also reported.     

Synthesis and characterization of polybinaphthalene incorporating chiral (R) or (S)-1,1′-binaphthalene and oxadiazole units by Heck reaction

Chiral conjugated polymers P-1 and P-2 were synthesized by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthalene ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthalene ((S)-M-1) with 2,5-bis(4-vinylphenyl)-1,3,4-oxadiazole (M-2) under Pd-catalyzed Heck coupling reaction, respectively. Both monomers and polymers were analysed by NMR, MS, FT-IR, UV, DSC-TG, fluorescent spectroscopy, GPC and CD spectra. The chiral conjugated polymers exhibit strong Cotton effect in their circular dichroism (CD) spectra indicating a high rigidity of polymer backbone. CD spectra of polymers P-1 and P-2 are almost identical and have opposite signs for their position. These polymers have strong blue fluorescence.     

Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₂-symmetric ligands, (R)-2,2′-bis(pyridin-2-ylmethylamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), (R)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (3H₂), (R)-2,2′-bis(diphenylphosphinoylamino)-6,6′-dimethyl-1,1′-biphenyl (4H₂), (R)-2,2′-bis(methanesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (5H₂), (R)-2,2′-bis(p-toluenesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (6H₂), and C₁-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), which are derived from (R)-2,2′-diamino-6,6′-dimethyl-1,1′-biphenyl. Treatment of M(NMe₂)₄ with 1 equiv. of N₄-ligand, 2H₂ or 3H₂ gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2)Zr(NMe₂)₂ (9), (3)Zr(NMe₂)₂ (11), and titanium amide (3)Ti(NMe₂)₂ (10), respectively, in good yields. Reaction of Zr(NMe₂)₄ with 1 equiv of diphenylphosphoramide 4H₂ affords the chiral zirconium amide (4)Zr(NMe₂)₂ (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe₂)₄ with 1 equiv. of sulphonylamide ligand, 5H₂ or 6H₂ gives, after recrystallization from a toluene solution, the chiral titanium amides (5)Ti(NMe₂)₂·0.5C₇H₈ (13·0.5C₇H₈) and (6)Ti(NMe₂)₂ (15), respectively, in good yields, while reaction of Zr(NMe₂)₄ with 1 equiv. of 5H₂ or 6H₂ gives the bis-ligated complexes, (5)₂Zr (14) and (6)₂Zr (16). Treatment of M(NMe₂)₄ with 2 equiv. of diphenylthiophosphoramide ligand 7H or N₃-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)₂Zr(NMe₂)₂ (17) and (8)₂Zr(NMe₂)₂ (19), and bis-ligated chiral titanium amide (8)₂Ti(NMe₂)₂ (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with moderate ee values, while the titanium amides are not.     

1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane and trimethylphosphite: unusual 1,4-dioxan-2,5-dione ring formation

1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane 1 reacted with trimethylphosphite giving two diastereomers, (Z)- and (E)-3,6-bis(trifluoromethyl)-3,6-bis(pentafluorophenyl)-1,4-dioxan-2,5-dione 2a, b in a 1:1 ratio, cyclodimerisation product of the intermediately generated α-lactone 4. Compounds 2a, b were hydrolysed to furnish 3,3,3-trifluoro-2-hydroxy-2-(2,3,4,5,6-pentafluorophenyl)propionic acid 5.     

(N-7-Azaindolyl)oligothiophenes: synthesis, characterization, and photophysical properties

The synthesis of a new series of mono- and oligothiophenes capped by 7-azaindoles such as 2-(N-azaindolyl)thiophene (1), 2-(N-azaindolyl)-5′-(bromo)oligothiophenes (2a-4a), and 2,5′-bis(N-azaindolyl)oligothiophenes (2b-4b) has been investigated. The reaction of 7-azaindole with 2-bromothiophene under the modified Ullmann condensation conditions led to the formation of 1. Simple extension of the same method to the reaction of 2,5′-dibromooligothiophenes in the presence of 4-5 M excess of 7-azaindole led to the formation of 2a-4a and 2b-4b in moderate overall yields (40-55%). All compounds were fully characterized by analytical and various spectroscopic techniques. The structures of 2b, 3b, and 4b were determined by X-ray diffraction analyses. All three compounds show several intermolecular C(π)?H interactions leading to the formation of herringbone packing in the solid-state structure. The UV absorption spectra of 1-4 consist of three characteristic electronic transitions corresponding to n→π^∗ and π→π^∗ transitions arising out of the π-conjugation of the entire molecule as well as local aromatic units. The emission spectra of the same compounds show intense fluorescence bands at the wavelengths between 422 and 495 nm. The length of the thiophene chain and the presence of bromine atom influence the band position of both absorption and emission spectra. While the extension in π-conjugation causes the reduction in the band gap, the bromine atom shifts the electronic transition energy to the blue region. The cyclic voltammetric measurements were performed with 1-4, which show that the compounds exhibit a typical pseudo-reversible redox wave with E_ox in the range 0.6-1.2 V.     

Dendritic BINOL ligands for asymmetric catalysis: effect of the linking positions and generations of the dendritic wedges on catalyst properties

Three types of new chiral BINOL ligands (2, 3 and 4) bearing dendritic wedges have been synthesized through coupling reaction between 3-hydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (7), 6,6′-dihydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (12), 6-hydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (15) and Fréchet-type polyether dendritic benzyl bromide, followed by deprotection of methoxymethyl groups by ⁱPrOH/HCl, respectively. These new ligands obtained were assessed in enantioselective Lewis acid-catalyzed addition of diethylzinc to benzaldehyde. Compared to the enantioselectivity observed with dendrimer 1 bearing the dendritic wedges at 3,3′-positions of the binaphthyl backbone, higher enantioselectivity for all these ligands was observed. Difference in the effect of linking positions and generations on enantioselectivity and/or activity for all three kinds of dendritic ligand-derived catalysts was observed. Among these dendritic ligands, (R)-3/Ti(IV) catalyst with the dendritic wedges at 6,6′-positions of BINOL gave the highest enantioselectivity (up to 87% ee).     

Stereochemical studies—XIII: Cyclic aminoalcohols and related compounds—VI synthesis of the four 2-amino-4-t-butylcyclopentanol isomers

From diethyl 3-t-butyladipate (5), via cis- and trans-4-t-butylcyclopentene-1,2-oxide (31, 32) as key compounds, the syntheses of cis-2-amino-cis-4-t-butylcyclopentanol (1), cis-2-amino-trans-4-t-butylcyclopentanol (2), trans-2-amino-cis-4-t-butylcyclopentanol (3) and trans-2-amino-trans-4-t-butylcyclopentanol (4) have been achieved. 1, 3 and 4 were also synthesized from the corresponding 2-hydroxy-4-t-butylcarboxylic acids by Curtius degradation of the hydrazides (11, 18, 19). The steric course of process leading to the above compounds is discussed.