Non‐iterative Asymmetric Synthesis of C15 Polyketide Spiroketals

The 2,2′‐methylenebis[furan] ( 1 ) was converted to 1‐{(4R,6S))‐6‐[(2R)‐2,4‐dihydroxybutyl]‐2,2‐dimethyl‐1,3‐dioxan‐4‐yl}‐3‐[(2R,4R)‐tetrahydro‐4,6‐dihydroxy‐2H‐pyran‐2‐yl)propan‐2‐one ((+)‐ 18 ) and its (4S)‐epimer (?)‐ 19 with high stereo‐ and enantioselectivity (Schemes 1–3). Under acidic methanolysis, (+)‐ 18 yielded a single spiroketal, (3R)‐4‐{(1R,3S,4′R,5R,6′S,7R)‐3′,4′,5′,6′‐tetrahydro‐4′‐hydroxy‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐6′‐yl}butane‐1,3‐diol ((?)‐ 20 ), in which both O‐atoms at the spiro center reside in equatorial positions, this being due to the tricyclic nature of (?)‐ 20 (methyl pyranoside formation). Compound (?)‐ 19 was converted similarly into the (4′S)‐epimeric tricyclic spiroketal (?)‐ 21 that also adopts a similar (3S)‐configuration and conformation. Spiroketals (?)‐ 20 , (?)‐ 21 and analog (?)‐ 23 , i.e., (1R,3S,4′R,5R,6′R)‐3′,4′,5′,6′‐tetrahydro‐6′‐[(2S)‐2‐hydroxybut‐3‐enyl]‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐4′‐ol, derived from (?)‐ 20 , were assayed for their cytotoxicity toward murine P388 lymphocytic leukemia and six human cancer cell lines. Only racemic (±)‐ 21 showed evidence of cancer‐cell‐growth inhibition (P388, ED₅₀: 6.9 μg/ml).     

Structural diversity of polynuclear MgxOy cores in magnesium phenoxide complexes

The binuclear complex bis(2,6‐di‐tert‐butyl‐4‐methylphenolato)‐1κO ,2κO‐(1,2‐dimethoxyethane‐1κ²O ,O ′)bis(μ‐phenylmethanolato‐1:2κ²O :O )(tetrahydrofuran‐2κO )dimagnesium(II), [Mg₂(C₇H₇O)₂(C₁₅H₂₃O)₂(C₄H₈O)(C₄H₁₀O₂)] or [(BHT)(DME)Mg(μ‐OBn)₂Mg(THF)(BHT)], (I), was obtained from the complex [(BHT)Mg(μ‐OBn)(THF)]₂ by substitution of one tetrahydrofuran (THF) molecule with 1,2‐dimethoxyethane (DME) in toluene (BHT is O‐2,6‐^t Bu₂‐4‐MeC₆H₄ and Bn is benzyl). The trinuclear complex bis(2,6‐di‐tert‐butyl‐4‐methylphenolato)‐1κO ,3κO‐tetrakis(μ‐2‐methylphenolato)‐1:2κ⁴O :O ;2:3κ⁴O :O‐bis(tetrahydrofuran)‐1κO ,3κO‐trimagnesium(II), [Mg₃(C₇H₇O)₄(C₁₅H₂₃O)₂(C₄H₈O)₂] or [(BHT)₂(μ‐O‐2‐MeC₆H₄)₄(THF)₂Mg₃], (II), was formed from a mixture of Bu₂Mg, [(BHT)Mg(ⁿ Bu)(THF)₂] and 2‐methylphenol. An unusual tetranuclear complex, bis(μ₃‐2‐aminoethanolato‐κ⁴O :O :O ,N )tetrakis(μ₂‐2‐aminoethanolato‐κ³O :O ,N )bis(2,6‐di‐tert‐butyl‐4‐methylphenolato‐κO )tetramagnesium(II), [Mg₄(C₂H₆NO)₆(C₁₅H₂₃O)₂] or Mg₄(BHT)₂(OCH₂CH₂NH₂)₆, (III), resulted from the reaction between (BHT)₂Mg(THF)₂ and 2‐aminoethanol. A polymerization test demonstrated the ability of (III) to catalyse the ring‐opening polymerization of ϵ‐caprolactone without activation by alcohol. In all three complexes (I)–(III), the BHT ligand demonstrates the terminal κO‐coordination mode. Complexes (I), (II) and (III) have binuclear rhomboid Mg₂O₂, trinuclear chain‐like Mg₃O₄ and bicubic Mg₄O₆ cores, respectively. A survey of the literature on known polynuclear Mg_x O_y core types for ArO–Mg complexes is also presented.     

Synthesis of spiro[indoline‐3,3′‐pyrrolizines] by 1,3‐dipolar reactions between isatins,l‐proline and electron‐deficient alkenes

Two spiro[indoline‐3,3′‐pyrrolizine] derivatives have been synthesized in good yield with high regio‐ and stereospecificity using one‐pot reactions between readily available starting materials, namely l ‐proline, substituted 1H‐indole‐2,3‐diones and electron‐deficient alkenes. The products have been fully characterized by elemental analysis, IR and NMR spectroscopy, mass spectrometry and crystal structure analysis. In (1′RS ,2′RS ,3SR ,7a′SR )‐2′‐benzoyl‐1‐hexyl‐2‐oxo‐1′,2′,5′,6′,7′,7a′‐hexahydrospiro[indoline‐3,3′‐pyrrolizine]‐1′‐carboxylic acid, C₂₈H₃₂N₂O₄, (I), the unsubstituted pyrrole ring and the reduced spiro‐fused pyrrole ring adopt half‐chair and envelope conformations, respectively, while in (1′RS ,2′RS ,3SR ,7a′SR )‐1′,2′‐bis(4‐chlorobenzoyl)‐5,7‐dichloro‐2‐oxo‐1′,2′,5′,6′,7′,7a′‐hexahydrospiro[indoline‐3,3′‐pyrrolizine], which crystallizes as a partial dichloromethane solvate, C₂₈H₂₀Cl₄N₂O₃·0.981CH₂Cl₂, (II), where the solvent component is disordered over three sets of atomic sites, these two rings adopt envelope and half‐chair conformations, respectively. Molecules of (I) are linked by an O—H…·O hydrogen bond to form cyclic R ₆⁶(48) hexamers of (S ₆) symmetry, which are further linked by two C—H…O hydrogen bonds to form a three‐dimensional framework structure. In compound (II), inversion‐related pairs of N—H…O hydrogen bonds link the spiro[indoline‐3,3′‐pyrrolizine] molecules into simple R ₂²(8) dimers.     

Lignans from the Bark of Magnolia kobus

The Et₂O‐soluble fraction from the bark of Magnolia kobus led to the isolation of two new lignans, (+)‐(7α,7′α,8α,8′α)‐3′,4,4′,5,5′‐pentamethoxy‐7,9′: 7′,9‐diepoxylignan‐3‐ol ( 1 ) and (+)‐(7α,7′α,8α,8′α)‐4,5‐dimethoxy‐3′,4′‐(methylenedioxy)‐7,9′: 7′,9‐diepoxylignan‐3‐ol ( 2 ), along with five known lignans 3 – 7 . Their structures were established on the basis of various spectroscopic analyses including 1D‐ (¹H, ¹³C, and DEPT) and 2D‐NMR (COSY, NOESY, HMQC, and HMBC) and by comparison of their spectral data with those of related compounds.     

Different nucleobase orientations in two cyclic 2′,3′‐phosphates of purine ribonucleosides: Et3NH(2′,3′‐cAMP) and Et3NH(2′,3′‐cGMP)·H2O

The crystal structures of triethyl­ammonium adenosine cyclic 2′,3′‐phosphate {systematic name: triethyl­ammonium 4‐(6‐amino­purin‐9‐yl)‐6‐hydroxy­methyl‐2‐oxido‐2‐oxoperhydro­furano[3,4‐c][1,3,2]dioxaphosphole}, Et₃NH(2′,3′‐cAMP) or C₆H₁₆N⁺·C₁₀H₁₁N₅O₆P⁻, (I), and guanosine cyclic 2′,3′‐phosphate monohydrate {systematic name: triethyl­ammonium 6‐hydroxy­methyl‐2‐oxido‐2‐oxo‐4‐(6‐oxo‐1,6‐dihydro­purin‐9‐yl)perhydro­furano[3,4‐c][1,3,2]dioxaphosphole monohydrate}, [Et₃NH(2′,3′‐cGMP)]·H₂O or C₆H₁₆N⁺·C₁₀H₁₁N₅O₇P⁻·H₂O, (II), reveal different nucleobase orientations, viz. anti in (I) and syn in (II). These are stabilized by different inter‐ and intra­molecular hydrogen bonds. The structures also exhibit different ribose ring puckering [₄E in (I) and ³T₂ in (II)] and slightly different 1,3,2‐dioxaphospho­lane ring conformations, viz. envelope in (I) and puckered in (II). Infinite ribbons of 2′,3′‐cAMP⁻ and helical chains of 2′,3′‐cGMP⁻ ions, both formed by O—H⋯O, N—H⋯X and C—H⋯X (X = O or N) hydrogen‐bond contacts, characterize (I) and (II), respectively.     

2′,3′‐Dehydrosalannol

The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)‐8‐(3‐furyl)‐2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c‐dodeca­hydro‐3‐hydroxy‐2a,5a,6a,7‐tetra­methyl‐5‐(3‐methylbut‐2‐enoyl­oxy)‐2H,3H‐cyclo­penta­[4′,5′]­furo­[2′,3′:6,5]benzo[cd]­isobenzo­furan‐6‐acetate, C₃₂H₄₂O₈, was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been found to possess antifeedant activity against Spodptera litura. The conformations of the functional groups are similar to those of 3‐des­acetyl­salannin, which was isolated from neem kernels. The mol­ecules are linked into chains by intermolecular O—H?O hydrogen bonds.     

The Ozonolysis of Longifolene: A Tool for the Preparation of Useful Chiral Compounds. Configuration Determination of New Stereogenic Centers by NMR Spectroscopy and X‐Ray Crystallography

The ozonolysis of (+)‐longifolene ( 1 ) in different solvents (Et₂O, CH₂Cl₂, CHCl₃, acetone) at ?80° provided quantitatively longifolene epoxide ( 3 ) as a single diastereoisomer in which the O‐atom is endo‐positioned (Scheme 2). Upon warming to room temperature, the epoxide remained stable only in acetone and was isolated as a low‐melting crystalline compound. In CH₂Cl₂, Et₂O, or CHCl₃ solution, epoxide 3 rapidly rearranged to the isomeric enols 4 and 5 , which underwent further rearrangement to give the exo‐aldehyde 6 . On standing for several weeks in CH₂Cl₂ solution, or in CHCl₃ and Et₂O as well, at room temperature, aldehyde 6 slowly rearranged into its epimer 7 . The aldehydes 6 and 7 were isolated on the preparative scale for further synthetic use. The addition of methylmagnesium iodide to 6 and 7 provided the corresponding alcohols 13 / 14 and 15 / 16 , respectively, which were isolated as pure diastereoisomers (Scheme 4). The configurations of the new chiral centers in 13 – 16 were determined by NMR methods and X‐ray crystallography.     

Four N7‐alkoxybenzyl‐substituted 4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐diones: hydrogen‐bonded supramolecular structures in zero,one, two or three dimensions

3‐tert‐Butyl‐7‐(4‐methoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₇N₃O₃, (I), 3‐tert‐butyl‐7‐(2,3‐dimethoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₂H₃₉N₃O₄, (II), 3‐tert‐butyl‐4′,4′‐dimethyl‐7‐(3,4‐methylenedioxybenzyl)‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₅N₃O₄, (III), and 3‐tert‐butyl‐4′,4′‐dimethyl‐1‐phenyl‐7‐(3,4,5‐trimethoxybenzyl)‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol 0.67‐solvate, C₃₃H₄₁N₃O₅·0.67C₂H₆O, (IV), all contain reduced pyridine rings having half‐chair conformations. The molecules of (I) and (II) are linked into centrosymmetric dimers and simple chains, respectively, by C—H...O hydrogen bonds, augmented only in (I) by a C—H...π hydrogen bond. The molecules of (III) are linked by a combination of C—H...O and C—H...π hydrogen bonds into a chain of edge‐fused centrosymmetric rings, further linked by weak hydrogen bonds into supramolecular arrays in two or three dimensions. The heterocyclic molecules in (IV) are linked by two independent C—H...O hydrogen bonds into sheets, from which the partial‐occupancy ethanol molecules are pendent. The significance of this study lies in its finding of a very wide range of supramolecular aggregation modes dependent on rather modest changes in the peripheral substituents remote from the main hydrogen‐bond acceptor sites.     

Regio‐ and stereospecific assembly of dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidines] from simple precursors using a one‐pot procedure: synthesis,spectroscopic and structural characterization,and a proposed mechanism of formation

The synthesis and characterization of three new dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine] compounds are reported, together with the crystal structures of two of them. (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐Chlorophenyl)‐1‐hexyl‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₂₈H₃₀ClN₃O₂S₂, (I), (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐chlorophenyl)‐1‐benzyl‐5‐methyl‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₃₀H₂₆ClN₃O₂S₂, (II), and (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐chlorophenyl)‐5‐fluoro‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₂₂H₁₇ClFN₃O₂S₂, (III), were each isolated as a single regioisomer using a one‐pot reaction involving l ‐proline, a substituted isatin and (Z)‐5‐(4‐chlorobenzylidene)‐2‐sulfanylidenethiazolidin‐4‐one [5‐(4‐chlorobenzylidene)rhodanine]. The compositions of (I)–(III) were established by elemental analysis, complemented by high‐resolution mass spectrometry in the case of (I); their constitutions, including the definition of the regiochemistry, were established using NMR spectroscopy, and the relative configurations at the four stereogenic centres were established using single‐crystal X‐ray structure analysis. A possible reaction mechanism for the formation of (I)–(III) is proposed, based on the detailed stereochemistry. The molecules of (I) are linked into simple chains by a single N—H…N hydrogen bond, those of (II) are linked into a chain of rings by a combination of N—H…O and C—H…S=C hydrogen bonds, and those of (III) are linked into sheets by a combination of N—H…N and N—H…S=C hydrogen bonds.     

Phenoxide and alkoxide complexes of Mg,Al and Zn,and their use for the ring‐opening polymerization of ϵ‐caprolactone with initiators of different natures

A new packing polymorph of bis(2,6‐di‐tert‐butyl‐4‐methylphenolato‐κO)bis(tetrahydrofuran‐κO)magnesium, [Mg(C₁₅H₂₃O)₂(C₄H₈O)₂] or Mg(BHT)₂(THF)₂, (BHT is the 2,6‐di‐tert‐butyl‐4‐methylphenoxide anion and THF is tetrahydrofuran), ( 1 ), has the same space group (P2₁) as the previously reported modification [Nifant'ev et al. (2017d). Dalton Trans. 46 , 12132–12146], but contains three crystallographically independent molecules instead of one. The structure of ( 1 ) exhibits rotational disorder of the tert‐butyl groups and positional disorder of a THF ligand. The complex of bis(2,6‐di‐tert‐butyl‐4‐methylphenolato‐κO)bis(μ₂‐ethyl glycolato‐κ²O,O′:κO)dimethyldialuminium, [Al₂(CH₃)₂(C₄H₇O₃)₂(C₁₅H₂₃O)₂] or [(BHT)AlMe(OCH₂COOEt)]₂, ( 2 ), is a dimer located on an inversion centre and has an Al₂O₂ rhomboid core. The 2‐ethoxy‐2‐oxoethanolate ligand (OCH₂COOEt) displays a μ₂‐κ²O,O′:κO semi‐bridging coordination mode, forming a five‐membered heteronuclear Al–O–C–C–O ring. The same ligand exhibits positional disorder of the terminal methyl group. The redetermined structure of the heptanuclear complex octakis(μ₃‐benzyloxo‐κO:κO:κO)hexaethylheptazinc, [Zn₇(C₂H₅)₆(C₇H₇O)₈] or [Zn₇(OCH₂Ph)₈Et₆], ( 3 ), possesses a bicubic Zn₇O₈ core located at an inversion centre and demonstrates positional disorder of one crystallographically independent phenyl group. Cambridge Structural Database surveys are given for complexes structurally analogous to ( 2 ) and ( 3 ). Complexes ( 2 ) and ( 3 ), as well as derivatives of ( 1 ), are of interest as catalysts for the ring‐opening polymerization of ϵ‐caprolactone, and polymerization results are reported.     

Cinerin C: a macrophyllin‐type bicyclo[3.2.1]octane neolignan from Pleurothyrium cinereum (Lauraceae)

The structure of naturally‐occurring cinerin C [systematic name: (7S,8R,3′R,4′S,5′R)‐Δ^8′‐4′‐hydroxy‐5,5′,3′‐trimethoxy‐3,4‐methylenedioxy‐2′,3′,4′,5′‐tetrahydro‐2′‐oxo‐7.3′,8.5′‐neolignan], isolated from the ethanol extract of leaves of Pleurothyrium cinereum (Lauraceae), has previously been established by NMR and HRMS spectroscopy, and its absolute configuration established by circular dichroism measurements. For the first time, its crystal strucure has now been established by single‐crystal X‐ray analysis, as the monohydrate, C₂₂H₂₆O₇·H₂O. The bicyclooctane moiety comprises fused cyclopentane and cyclohexenone rings which are almost coplanar. An intermolecular O—H...O hydrogen bond links the 4′‐OH and 5′‐OCH₃ groups along the c axis.     

Enantioselective Access to (−)‐Ambrox® Starting from β‐Farnesene

Starting from inexpensive (E)‐β‐farnesene ( 1 ), an eight‐step enantioselective synthesis of the olfactively precious Ambrox^® ((?)‐ 2a ) has been performed. The crucial step is the catalytic asymmetric isomerization of (2E,6E)‐N,N‐diethylfarnesylamine ( 3 ) to the corresponding enamine (?)‐(R,E)‐ 4a , applying Takasago's well‐known industrial methodology. The resulting dihydrofarnesal ((+)‐(R)‐ 5 ) (90% yield, 96% ee), obtained after in situ hydrolysis (AcOH, H₂O), was then cyclized under catalytic SnCl₄ conditions, via its corresponding unreported enol acetate (?)‐(R)‐ 4b , to afford trans‐decalenic aldehyde (+)‐ 6a . Subsequent transformations furnished bicyclic ketone (?)‐ 8a and unsaturated nitrile (+)‐ 11 , both reported as intermediates to access to (?)‐ 2a .     

Stereoselective Conversion of Campholene- to Necrodane-Type Monoterpenes. Novel Access to (−)-(R,R)- and (R,S)-α-Necrodol and the Enantiomeric γ-Necrodols

Naturally occurring (?)-(R,R)-α-necrodol ((?)- 1 ) and its C(4)-epimer (?)- 2 are obtained in 84 and 44% yields, respectively, by lithium ethylenediamide (LEDA) treatment of the corresponding β-necrodols (?)- 3 and (?)- 4 (Scheme 1, Table), both readily available from (?)-campholenyl acetate ((?)- i ) by an efficient stereoselective synthesis. The thermodynamically preferred (?)-(R)-γ-necrodol ((?)- 5 ) becomes the major product (≥ 80% yield) after either prolonged treatment with LEDA or exposure of α- and β-necrodols to BF₃·Et₂O. In an alternative route, (+)- 5 is prepared starting from (+)-campholenal ((+)- ii ) via Pd-catalysed decarbonylation to (?)-(S)-1,4,5,5-tetramethylcyclopent-l-ene ((?)- 6 ) and subsequent application of an acid-catalysed CH₂O-addition/rearrangement sequence (Scheme 2).     

Synthesis of 5‐[2‐(guanin‐9‐yl)‐ and 5‐[2‐(2‐aminopurin‐9‐yl)ethyl]‐2‐D‐ribo‐(1,2′,3′,4′‐tetrahydroxybutyl)‐1,3‐dioxane

Stereoselective synthesis of 5‐[2‐(guanin‐9‐yl)‐ and 5‐[2‐(2‐aminopurin‐9‐yl)ethyl]‐2‐D‐ribo‐(1′,2′,3′,4′‐tetrahydroxybutyl)‐1,3‐dioxane, 2‐5, as potential prodrugs of penciclovir, has been accomplished in six steps from readily available 2,3,4,5‐tetra‐O‐acetyl‐aldehydo‐D‐ribose ( 6 ) and the 1,3‐diol 7 . It has been demonstrated that the use of boron trifluoride diethyl etherate (BF₃·Et₂O) in dichloromethane along with excess anhydrous copper(II) sulfate was crucial for the efficient formation of cyclic acetal 8 . In addition, the chromatographic separation of cis and trans isomers of the cyclic acetal at the bromide stage 10 was feasible, which was requisite for the successful stereoselective synthesis of the ribosyl derivatives 2–5 .     

Two stereoisomeric pentacyclic oxin­dole alkaloids from Uncaria tomentosa: uncarine C and uncarine E

The chloro­form solvate of uncarine C (pteropodine), (1′S,3R,4′aS,5′aS,10′aS)‐1,2,5′,5′a,7′,8′,10′,10′a‐octa­hydro‐1′‐methyl‐2‐oxospiro­[3H‐indole‐3,6′(4′aH)‐[1H]­pyrano­[3,4‐f]indolizine]‐4′‐carboxyl­ic acid methyl ester, C₂₁H₂₄N₂O₄·CHCl₃, has an absolute configuration with the spiro C atom in the R configuration. Its epimer at the spiro C atom, uncarine E (isopteropodine), (1′S,3S,4′aS,5′aS,10′aS)‐1,2,5′,5′a,7′,8′,10′,10′a‐octahydro‐1′‐methyl‐2‐oxospiro[3H‐indole‐3,6′(4′aH)‐[1H]pyrano[3,4‐f]indolizine]‐4′‐carboxylic acid methyl ester, C₂₁H₂₄N₂O₄, has Z′ = 3, with no solvent. Both form intermolecular hydrogen bonds involving only the ox­indole, with N?O distances in the range 2.759 (4)–2.894 (5) Å.     

Minimally Competent Lewis Acid Catalysts: Indium(III) and Bismuth(III) Salts Produce Rhamnosides (=6‐Deoxymannosides) in High Yield and Purity

Glycosylation of decan‐1‐ol ( 2 ), (±)‐decan‐2‐ol ( 3 ), and (±)‐methyl 3‐hydroxydecanoate ( 4 ) with L ‐rhamnose peracetate 5 to produce rhamnosides (=6‐deoxymannosides) 6, 7 , and 8 in the presence of Lewis acids BF₃?Et₂O, Sc(OTf)₃, InBr₃, and Bi(OTf)₃ was studied (Table 1). While the strong Lewis acids BF₃?Et₂O and Sc(OTf)₃ were effective as glycosylation promoters, they had to be used in excess; however, glycosylation required careful control of reaction times and temperatures, and these Lewis acids produced impurities in addition to the desired glycosides. Enantiomerically pure rhamnosides (R)‐ 1 and (S)‐ 1 (Fig.) were obtained from L ‐rhamnose peracetate 5 and (±)‐benzyl 3‐hydroxydecanoate ( 9 ) via the diastereoisomeric rhamnosides 10 (Table 2; Scheme 3). The much weaker Lewis acids InBr₃ and Bi(OTfl)₃ produced purer products in high yield under a wider range of conditions (higher temperatures), and were effective glycosylation promoters even when used catalytically (<10% catalyst; Table 2). We refer to these Lewis acids as ‘minimally competent Lewis acids’ (cf. Scheme 4).     

(±)‐6‐tert‐Butyl‐8‐hydroxymethyl‐2‐­phenyl‐4H‐1,3‐benzodioxin and 2,2,2′,2′,6,6′‐hexamethyl‐8,8′‐methylenebis(4H‐1,3‐benzodioxin)

Two compounds containing 1,3‐benzodioxin groups are reported, namely (±)‐6‐tert‐butyl‐8‐hydroxy­methyl‐2‐phenyl‐4H‐1,3‐benzodioxin, C₁₉H₂₂O₃, (I), and 2,2,2′,2′,6,6′‐hexamethyl‐8,8′‐methyl­enebis(4H‐1,3‐benzodioxin), C₂₃H₂₈O₄, (II).The hydroxy groups of neighbouring mol­ecules in (I) are hydrogen bonded to each other, giving rise to double‐row chains. The mol­ecule in (II) adopts a `butterfly' conformation, with the O atoms in distal positions. In both compounds, the dioxin rings are in distorted half‐chair conformations.     

The Aggregation Behavior of Butyllithium in Diethyl Ether in the Presence of LiBr,LiClO4, and Phenyllithium: A Deuterium‐Induced Secondary 6Li‐NMR Isotope‐Effect Study

The aggregation of BuLi (LiR) in diethyl ether (Et₂O) in the presence of LiBr was studied by ⁶Li‐ and ¹³C‐NMR spectroscopy. For a 1.0 : 0.8 mixture of both species, the clusters (LiR)₄, Li₄R₃Br, Li₄R₂Br₂, Li₄RBr₃, and/or Li₂RBr in the ratio 7 : 81 : 12 with Li₄RBr₃ and/or Li₂RBr<1 were detected with the isotopic fingerprint method that is based on secondary deuterium (D)‐induced isotope shifts for δ(Li). The raising content of bromide ions causes increased shielding for δ(Li). As in the case of a 1 : 1 MeLi/LiBr mixture in Et₂O, cluster Li₄R₃Br is the most stable one. In the presence of N,N,N′,N′‐tetramethylethylenediamine (TMEDA), only a mixed dimer was found. For LiClO₄, no inclusion of the ClO$\rm{{_{4}^{-}}}$ ion could be detected. A mixture BuLi/PhLi 1 : 1 in Et₂O in the presence of TMEDA showed only dimers with the mixed dimer as the most stable cluster. Chemical exchange of Li between the two homodimers was detected by EXSY spectroscopy. This implies an exchange mechanism with a fluxional tetramer as intermediate.     

Azadirachtol,a tetranortriterpenoid from neem kernels

The title compound, di­methyl (?)‐(2aR,3R,4R,4aS,5R,7aS,8R,10S,10aR)‐3,8,10‐tri­hydroxy‐4‐[(2R,6R)‐2‐hydroxy‐11‐methyl‐5,7,10‐trioxatetra­cyclo­[6.3.1.0^2,60^9,11]­dodec‐3‐en‐9‐yl]‐4‐methyl­per­hydro­isobenzo­furano­[5,4,3a‐cd]­isobenzofuran‐5,10a‐di­acetate, C₂₈H₃₆O₁₃, which exhibits higher antifeedant activity than azadirachtin‐A, a known potent antifeedant, was isolated from neem kernels. The asymmetric unit of the structure contains two independent mol­ecules, which differ in the conformations of their functional groups and also in the conformations of some of the rings. The relative orientation between the decalin and furan­yl moieties is similar to that observed in the majority of azadirachtin structures, but is different from that in azadirachtin‐A. The two symmetry‐independent mol­ecules are linked into dimeric units by intermolecular O—H?O hydrogen bonds.     

Preparation and Absolute Configuration of (−)-(E)-α-trans-Bergamotenone

The synthesis, absolute configuration, and olfactive evaluation of (?)-(E)-α-trans-bergamotenone (= (?)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (?)- 1 ), as well as its homologue (?)- 19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (?)-α-trans-bergamotene (= (?)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (?)- 2 ), together with those of the structurally related aldehydes (?)- 3a,b and alcohols (?)- 4a,b , have been rigorously assigned.