Exo Diels–Alder adducts between ortho‐ and para‐N‐acetoxy­phenyl­male­imides and furan

In exo‐2‐(3,5‐dioxo‐10‐oxa‐4‐aza­tri­cyclo­[5.2.1.0^2,6]­dec‐8‐en‐4‐yl)­phenyl acetate, C₁₆H₁₃NO₅, the plane of the acetoxy group lies almost perpendicular to that of the phenyl ring [dihedral angle = 89.8 (1)°], in contrast with the smaller deviations found in the para isomer exo‐4‐(3,5‐dioxo‐10‐oxa‐4‐aza­tri­cyclo­[5.2.1.0^2,6]­dec‐8‐en‐4‐yl)­phenyl acetate, C₁₆H₁₃NO₅, these being 63.6 (1) and 37.0 (1)° for the two crystallographically independent mol­ecules. Irrespective of the position of the acetoxy group, both compounds pack through soft C—H⋯X (X is O or phenyl) interactions, forming interlinked centrosymmetric tetramers in the bc plane.     

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).     

Synthesis and Self‐Aggregation of Enantiopure and Racemic Molecular Tweezers Based on the Bicyclo[3.3.1]nonane Framework

A pair of molecular tweezers (syn‐ 4 ) that consists of quinoline and pyrazine units fused to a bicyclic framework is presented. The tweezers were synthesised both as a racemic mixture (rac‐ 4 ) and an enantiomerically pure form ((R,R,R,R)‐ 4 ) starting from either racemic or enantiomerically pure bicyclo[3.3.1]nonane‐2,6‐dione ( 3 ). Homochiral dimers were observed in the solid state for rac‐ 4 . The self‐association of both rac‐ 4 and (R,R,R,R)‐ 4 was studied in solution. A weak self‐association constant in CDCl₃ was estimated by ¹H NMR spectroscopic dilution titration experiments in both cases, following several proton resonances. For this purpose, a general normalisation model for the accurate determination of association constants from multiple datasets was developed. In contrast to the solid state, no diastereomeric discrimination was observed for rac‐ 4 in solution.     

Disila‐Galaxolide and Derivatives: Synthesis and Olfactory Characterization of Silicon‐Containing Derivatives of the Musk Odorant Galaxolide

A series of silicon‐containing derivatives of the polycyclic musk odorant galaxolide ( 4 a ) was synthesized, that is, disila‐galaxolide ((4RS,7SR)‐ 4 b /(4RS,7RS)‐ 4 b ), its methylene derivative rac‐ 9 , and its nor analogue rac‐ 10 . The tricyclic title compounds with their 7,8‐dihydro‐6,8‐disila‐6 H‐cyclopenta[g]isochromane skeleton were prepared in multistep syntheses by using a cobalt‐catalyzed [2+2+2] cycloaddition of the mono‐ yne H₂C?CHCH₂OCH₂C?CB(pin) (B(pin)=4,4,5,5‐tetramethyl‐1,3,2‐di‐ oxaborolan‐2‐yl) with the diynes H₂C?C[Si(CH₃)₂C?CH]₂ or H₂C‐ [Si(CH₃)₂C?CH]₂ as the key step. Employing [Cr(CO)₃(MeCN)₃] as an auxiliary, the disila‐galaxolide diastereomers (4RS,7SR)‐ 4 b and (4RS,7RS)‐ 4 b could be chromatographically separated through their tricarbonylchromium(0) complexes, followed by oxidative decomplexation. The identity of the title compounds and their precursors was established by elemental analyses and multinuclear NMR spectroscopic studies and in some cases additionally by crystal structure analyses. Compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 were characterized for their olfactory properties, including GC‐olfactory studies of the racemic compounds on a chiral stationary phase. As for the parent galaxolide stereoisomers 4 a , only one enantiomer of the silicon compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 , smelt upon enantioselective GC‐olfactometry, which according to the elution sequence is assumed to be also (4S)‐configured as in the case of the galaxolide stereoisomers. The disila‐analogues (4S,7R)‐ 4 b and (4S,7S)‐ 4 b were, however, about one order of magnitude less intense in terms of their odor threshold than their parent carbon compounds (4S,7R)‐ 4 a and (4S,7S)‐ 4 a . The introduction of a 7‐methylene group in disila‐galaxolide ( 4 b →rac‐ 9 ) improved the odor threshold by a factor of two. With the novel silicon‐containing galaxolide derivatives, the presumed hydrophobic bulk binding pocket of the corresponding musk receptor(s) could be characterized in more detail, which could be useful for the design of novel musk odorants with an improved environmental profile.     

Chirality‐ and pH‐Controlled Supramolecular Isomerism in Cobalt Phosphonates and Its Impact on the Magnetic Behavior

Two pairs of enantiomeric compounds with formulas (S)‐ or (R)‐Co₃(ppap)₂(4,4′‐bpy)₂(H₂O)₂ ? 4 H₂O [(S)‐ 1 or (R)‐ 1 ], (S)‐ or (R)‐Co₃(ppap)₂(4,4′‐bpy)₂(H₂O)₂ ? 3 H₂O [(S)‐ or (R)‐ 2 ), and related racemic compound Co₃(ppap)₂(4,4′‐bpy)₂(H₂O)₂ ? 4 H₂O (rac‐ 3 ; 4,4′‐bpy=4,4′‐bipyridine, H₃ppap=3‐phenyl‐2‐[(phosphonomethyl)amino]propanoic acid) are reported. Compounds 1 and rac‐ 3 show identical three‐dimensional framework structures, whereas compounds 2 have two‐dimensional layer structures. Compounds 1 and 2 are catenation isomers, formation of which is controlled solely by the pH of the reaction mixtures, whereas the formation of isomeric compounds 1 and rac‐ 3 is controlled purely by the chirality of the phosphonate ligand. The magnetic properties of fully dehydrated (S)‐ 1 , (S)‐ 2 , and rac‐ 3 are highly dependent on both structure and chirality.     

Alkylations of tricyclo[5.2.1.0]deca-4,8-dien-3-one by a cuprate reaction

Alkylation at C₆ of tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one (R=H) was achieved by treatment of 6-bromotricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one with lithium dimethylcuprate and subsequently with an appropriate electrophile. The best results were obtained in THF as the solvent. A wide range of alkyl halides, bromo ketones and esters, and acetyl chloride resulted in C₆-tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-ones in moderate to good yields. This alkylation reaction proceeds via a C₆-carbanionic Cu intermediate, which is likely stabilized by the enone olefinic bond. 6-Bromo-endo-tricyclo[5.2.1.0^2,6]dec-8-en-3-one, which lacks this double bond, behaves differently. Treatment with lithium dimethylcuprate leads to dehydrobromination to give tricyclo[5.2.1.0^2,6]deca-2(6),8-dien-3-one in high yield.     

A convenient route to prepare isodicyclopentadiene—precursor of 1,5-dihydro-pentalene

A new route to prepare tricyclo[5.2.1.0^2,6]deca-2,4-diene (isodicyclopentadiene) was developed. This new route passes through a brominated (5-bromotricyclo[5.2.1.0^2,6]dec-3-ene) derivative obtained from tricycle[5.2.1.0^2,6]dec-3-ene (8,9-dihydrodicyclopentadiene) and NBS with a good yield. The complete assignment of protons and carbons on nuclear magnetic resonance spectra was done for dicyclopentadiene and the chemically transformed compounds by 2D NMR techniques.     

Zn(II) and Cu(II) unsymmetrical formamidine complexes as effective initiators for ring‐opening polymerization of cyclic esters

A series of Zn(II) and Cu(II) complexes were synthesized using unsymmetrical N,N′‐ diarylformamidine ligands, i.e. N‐(2‐methoxyphenyl)‐N′‐2,6‐dichorophenyl)‐formamidine ( L1 ), N‐(2‐methoxyphenyl)‐N′‐phenyl)‐formamidine ( L2 ), N‐(2‐methoxyphenyl)‐N′‐(2,6‐dimethylphenyl)‐formamidine ( L3 ) and N‐(2‐methoxyphenyl)‐N′‐(2,6‐diisopropylphenyl)‐formamidine ( L4 ). The complexes, [Zn₂( L1 )₂(OAc)₄] ( 1) , [Zn₂( L2 )₂(OAc)₄] ( 2 ), [Zn₂( L3 )₂(OAc)₄] ( 3 ), [Zn₂( L4 )₂(OAc)₄] ( 4 ), [Cu₂( L1 )₂(OAc)₄] ( 5 ), [Cu₂( L2 )₂(OAc)₄] ( 6 ), [Cu₂( L3 )₂(OAc)₄] ( 7 ) and [Cu₂( L4 )₂(OAc)₄] ( 8 ), were prepared via a mechanochemical method with excellent yields between 95 ‐ 98% by reacting the metal acetates and corresponding ligands. Structural studies showed that both complexes are dimeric with a paddlewheel core structure in which the separation between the two metal centres are 2.9898 (8) and 2.6653 (7) Å in complexes 3 and 7 , respectively. Complexes 1 – 8 were used in ring‐opening polymerization of ε‐caprolactone (ε‐CL) and rac‐lactide (rac‐LA). Zn(II) complexes were more active than Cu(II) complexes, with complex 1 bearing electron withdrawing chloro groups being the most active (k_app = 0.0803 h^‐1). Low molecular weight poly‐(ε‐CL) and poly‐(rac‐LA) ranging from 1720 to 6042 g mol^‐1, with broad molecular weight distribution (PDIs, 1.78 – 1.87) were obtained. Complex 2 gave reaction orders of 0.56 and 1.52 with respect to ε‐CL and rac‐LA, respectively.     

Metabolism of Deuterated Isomeric 6,7‐Dihydroxydodecanoic Acids in Saccharomyces cerevisiae – Diastereo‐ and Enantioselective Formation and Characterization of 5‐Hydroxydecano‐4‐lactone (=4,5‐Dihydro‐5‐(1‐hydroxyhexyl)furan‐2(3H)‐one) Isomers

The chemical synthesis of deuterated isomeric 6,7‐dihydroxydodecanoic acid methyl esters 1 and the subsequent metabolism of esters 1 and the corresponding acids 1a in liquid cultures of the yeast Saccharomyces cerevisiae was investigated. Incubation experiments with (6R,7R)‐ or (6S,7S)‐6,7‐dihydroxy(6,7‐²H₂)dodecanoic acid methyl ester ((6R,7R)‐ or (6S,7S)‐(6,7‐²H₂)‐ 1 , resp.) and (±)‐threo‐ or (±)‐erythro‐6,7‐dihydroxy(6,7‐²H₂)dodecanoic acid ((±)‐threo‐ or (±)‐erythro‐(6,7‐²H₂)‐ 1a , resp.) elucidated their metabolic pathway in yeast (Tables 1–3). The main products were isomeric ²H‐labeled 5‐hydroxydecano‐4‐lactones 2 . The absolute configuration of the four isomeric lactones 2 was assigned by chemical synthesis via Sharpless asymmetric dihydroxylation and chiral gas chromatography (Lipodex ^® E). The enantiomers of threo‐ 2 were separated without derivatization on Lipodex ^® E; in contrast, the enantiomers of erythro‐ 2 could be separated only after transformation to their 5‐O‐(trifluoroacetyl) derivatives. Biotransformation of the methyl ester (6R,7R)‐(6,7‐²H₂)‐ 1 led to (4R,5R)‐ and (4S,5R)‐(2,5‐²H₂)‐ 2 (ratio ca. 4 : 1; Table 2). Estimation of the label content and position of (4S,5R)‐(2,5‐²H₂)‐ 2 showed 95% label at C(5), 68% label at C(2), and no ²H at C(4) (Table 2). Therefore, oxidation and subsequent reduction with inversion at C(4) of 4,5‐dihydroxydecanoic acid and transfer of ²H from C(4) to C(2) is postulated. The 5‐hydroxydecano‐4‐lactones 2 are of biochemical importance: during the fermentation of Streptomyces griseus, (4S,5R)‐ 2 , known as L‐factor, occurs temporarily before the antibiotic production, and (?)‐muricatacin (=(4R,5R)‐5‐hydroxy‐heptadecano‐4‐lactone), a homologue of (4R,5R)‐ 2 , is an anticancer agent.     

Synthesis of diesters by addition of saturated carboxylic acids to tricyclodecenyl formate

Reaction of addition of C₁-C₅-saturated monobasic acids to tricyclo[5.2.1.0^2.6]dec-3-en-8(9)-yl for-mate in the presence of a catalyst, boron trifluoride etherate (BF₃·OEt₂), was used to synthesize homo- and mixed tricyclo[5.2.1.0^2.6]decane-3(4),8(9)-diol diesters. The synthesized formic-acetic and formic-propionic acid diesters have a pleasant odor and can be used as components for preparation of perfume formulations.     

Synthesen von Tricyclo [5.2.1.04,8]decan (2-Homobrendan)

Syntheses of Tricyclo [5.2.1.0^4,8]decane (2-Homobrendane) Three different approaches to tricyclo [5.2.1.0^4,8] decane (5) (and derivatives thereof), one of the 19 isomeric hydrocarbons of the ‘adamantaneland’, are described: (1) Cyclization of properly functionalized bicyclo [3.2.1]octanes as 32 (cyclialkylation), 40+42 (thermocyclization) and 44+45 (photocyclization); (2) Silver-(I)-ion catalyzed rearrangement of 5,7- and 5,10-Dehydroprotoadamantane ( 63 and 64 , respectively) yielding tricyclo[5.2.1.0^4,8]dec-2- (39) and -5-ene (59) , respectively; (3) Thermal eliminative rearrangement of the 10endo-p-toluenesulfonate and -methanesulfonate of protoadamantane ( 71 and 72 ) and protoadamant-4-ene ( 76 and 77 ), respectively, yielding tricyclo [5.2.1.0^4,8]dec-2-ene (39) and -2, 5-diene (15) , respectively.     

Stereoselective Reduction of `Capsanthol‐3′‐ones' (=3,6′‐Dihydroxy‐β,κ‐caroten‐3′‐ones) by Complex Hydrides

The (3R,5′R,6′R)‐ and (3R,5′R,6′S)‐capsanthol‐3′‐one (=3,6′‐dihydroxy‐β,κ‐caroten‐3′‐one; 4 and 5 , resp.) were reduced by different complex metal hydrides containing organic ligands. The ratio of the thus obtained diastereoisomeric (3′S)‐capsanthols 2 and 3 or (3′R)‐capsanthols 6 and 7 , respectively, was investigated. Four complex hydrides showed remarkable stereoselectivity and produced the (3′R,6′S)‐capsanthol ( 6 ) in 80 – 100% (see Table 1). The starting materials and the products were characterized by UV/VIS, CD, ¹H‐ and ¹³C‐NMR, and mass spectra.     

Synthesis of bi- and tricyclic acrylates in the presence of boron trifluoride etherate

The addition of acrylic acid to bicyclo[2.2.1]heptene hydrocarbons and tricyclo[5.2.1.0^2,6]deca-3,8-diene catalyzed with BF₃·O(C₂H₅)₂ was studied and bi- and tricyclic esters of acrylic acid were synthesized that were reactive monomers for preparation of macromolecular compounds.     

Stereoselective Synthesis of 8‐Oxabicyclo[3.2.1]octane‐2,3,4,6,7‐pentols and Total Asymmetric Synthesis of 2,6‐Anhydrohepturonic Acid Derivatives and of β‐C‐manno‐Pyranosides Suitable for the Construction of (1→3)‐C,C‐Linked Trisaccharides

Enantiomerically pure (+)‐(1S,4S,5S,6S)‐6‐endo‐(benzyloxy)‐5‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((+)‐ 5 ) and its enantiomer (−)‐ 5 , obtained readily from the Diels‐Alder addition of furan to 1‐cyanovinyl acetate, can be converted with high stereoselectivity into 8‐oxabicyclo[3.2.1]octane‐2,3,4,6,7‐pentol derivatives (see 23 – 28 in Scheme 2). A precursor of them, (1R,2S,4R,5S,6S,7R,8R)‐7‐endo‐(benzyloxy)‐8‐exo‐hydroxy‐3,9‐dioxatricyclo[4.2.1.0^2,4]non‐5‐endo‐yl benzoate ((−)‐ 19 ), is transformed into (1R,2R,5S, 6S,7R,8S)‐6‐exo,8‐endo‐bis(acetyloxy)‐2‐endo‐(benzyloxy)‐4‐oxo‐3,9‐dioxabicyclo[3.3.1]non‐7‐endo‐yl benzoate ((−)‐ 43 ) (see Scheme 5). The latter is the precursor of several protected 2,6‐anhydrohepturonic acid derivatives such as the diethyl dithioacetal (−)‐ 57 of methyl 3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐D ‐glycero‐D ‐galacto‐hepturonate (see Schemes 7 and 8). Hydrolysis of (−)‐ 57 provides methyl 3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐D ‐glycero‐D ‐galacto‐hepturonate 48 that undergoes highly diastereoselective Nozaki‐Oshima condensation with the aluminium enolate resulting from the conjugate addition of Me₂AlSPh to (1S,5S,6S,7S)‐7‐endo‐(benzyloxy)‐6‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐8‐oxabicyclo[3.2.1]oct‐3‐en‐2‐one ((−)‐ 13 ) derived from (+)‐ 5 (Scheme 12). This generates a β‐C‐mannopyranoside, i.e., methyl (7S)‐3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐7‐C‐[(1R,2S,3R,4S,5R,6S,7R)‐6‐endo‐(benzyloxy)‐7‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐4‐endo‐hydroxy‐2‐exo‐(phenylthio)‐8‐oxabicyclo[3.2.1]oct‐3‐endo‐yl]‐L ‐glycero‐D ‐manno‐heptonate ((−)‐ 70 ; see Scheme 12), that is converted into the diethyl dithioacetal (−)‐ 75 of methyl 3‐O‐acetyl‐2,6‐anhydro‐4,5‐dideoxy‐4‐C‐{[methyl (7S)‐3,5,7‐tri‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐L ‐glycero‐D ‐manno‐heptonate]‐7‐C‐yl}‐5‐C‐(phenylsulfonyl)‐L ‐glycero‐D ‐galacto‐hepturonate ( 76 ; see Scheme 13). Repeating the Nozaki‐Oshima condensation to enone (−)‐ 13 and the aldehyde resulting from hydrolysis of (−)‐ 75 , a (1→3)‐C,C‐linked trisaccharide precursor (−)‐ 77 is obtained.     

Breaking the Mirror: pH‐Controlled Chirality Generation from a meso Ligand to a Racemic Ligand

To study the conversion from a meso form to a racemic form of tetrahydrofurantetracarboxylic acid (H₄L), seven novel coordination polymers were synthesized by the hydrothermal reaction of Zn(NO₃)₂ ? 6 H₂O with (2S,3S,4R,5R)‐H₄L in the presence of 1,10‐phenanthroline (phen), 2,2′‐bipyridine (2,2′‐bpy), or 4,4′‐bipyridine (4,4′‐bpy): [Zn₂{(2S,3S,4R,5R)‐L}(phen)₂(H₂O)] ? 2 H₂O ( 1 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L}(phen)₂(H₂O)₂] ( 2 ), [Zn₂{(2S,3S,4R,5R)‐L}(H₂O)₂] ? H₂O ( 3 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L} (2,2′‐bpy)₂(H₂O)₂] ? 2 H₂O ( 4 ), [Zn₂ {(2S,3S,4R,5R)‐L}(2,2′‐bpy)(H₂O)] ( 5 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L} (4,4′‐bpy)₂(H₂O)₂] ( 6 ), and [Zn₂ {(2S,3S,4R,5R)‐L}(4,4′‐bpy)(H₂O)] ? 2 H₂O ( 7 ). These complexes were obtained by control of the pH values of reaction mixtures, with an initial of pH 2.0 for 1 , 2.5 for 2 , 4 , and 6 , and 4.5 for 3 , 5 , and 7 , respectively. The expected configuration conversion has been successfully realized during the formation of 2 , 4 , and 6 , and the enantiomers of L, (2S,3R,4R,5R)‐L and (2S,3S,4S,5R)‐L, are trapped in them, whereas L ligands in the other four complexes retain the original meso form, which indicates that such a conversion is possibly pH controlled. Acid‐catalyzed enol–keto tautomerism has been introduced to explain the mechanism of this conversion. Complex 1 features a simple 1D metal–L chain that is extended into a 3D supramolecular structure by π–π packing interactions between phen ligands and hydrogen bonds. Complex 2 has 2D racemic layers that consist of centrosymmetric bimetallic units, and a final 3D supramolecular framework is formed by the interlinking of these layers through π–π packing interactions of phen. Complex 3 is a 3D metal–organic framework (MOF) involving meso‐L ligands, which can be regarded as (4,6)‐connected nets with vertex symbol (4⁵.6)(4⁷.6⁸). Complexes 4 and 5 contain 2D racemic layers and (6,3)‐honeycomb layers, respectively, both of which are combined into 3D supramolecular structures through π–π packing interactions of 2,2′‐bpy. The structure of complex 6 is a 2D network formed by 4,4′‐bpy bridging 1D tubes, which consist of metal atoms and enantiomers of L. These layers are connected through hydrogen bonds to give the final 3D porous supramolecular framework of 6 . Complex 7 is a 3D MOF with novel (3,4,5)‐connected (6³)(4².6⁴)(4².6⁶.8²) topology. The thermal stability of these compounds was also investigated.     

An Efficient Synthesis of Spiro‐oxindole Derivatives by Three‐Component Reactions in Water

An efficient synthesis of (3S)‐1,1′,2,2′,3′,4′,6′,7′‐octahydro‐9′‐nitro‐2,6′‐dioxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carbonitrile is achieved via a three‐component reaction of isatin, ethyl cyanoacetate, and 1,2,3,4,5,6‐hexahydro‐2‐(nitromethylidene)pyrimidine. The present method does not involve any hazardous organic solvents or catalysts. Also the synthesis of ethyl 6′‐amino‐1,1′,2,2′,3′,4′‐hexahydro‐9′‐nitro‐2‐oxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carboxylates in high yields, at reflux, using a catalytic amount of piperidine, is described. The structures were confirmed spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS data) and by elemental analyses. A plausible mechanism for this reaction is proposed (Scheme 2).     

Intramolecular [4+2] cycloaddition of furfurylsubstituted homoallylamines to allylhalides,acryloyl chloride and maleic anhydride

Acylation of 4‐(furyl‐2)‐4‐R‐aminobut‐1‐enes and 4‐R‐4‐furfurylaminobut‐1‐enes with maleic anhydride, acryloyl chloride or allylhalides provided 3‐aza‐10‐oxatricyclo[5.2.1.0^1,5]decenes. The tricycles are formed via an initial amide formation followed by a stereoselective exo‐IMDAF (Intramolecular Diels‐Alder of Furan). In case of competing cycloaddition (for compounds possessing two furan or two dienophilic moieties) the most substituted fivemembered cycle is preferably annulated. Refluxing of 4‐R‐4‐furfurylaminobut‐1‐enes in acetic anhydride led to exo‐3‐aza‐11‐oxatricyclo[6.2.1.0^1,6]undecenes with the pseudoequatorial substituent R‐4. Treatment of 3‐aza‐10‐oxatricyclo[5.2.1.0^1,5]decenes with PPA at 90?110°C promoted cyclic ether opening, aromatization and intramolecular cyclization reactions sequence to give the corresponding tetracyclic compounds — tetrahydroisoindolo[2,1‐a]quinolines and tetrahydroisoindolo[2,1‐b][2]benzazepines in good yields. Unusual products of ipso‐substitution in aromatic ring were obtained on cyclization of N‐p‐R‐substituted 2‐allyl‐4‐oxo‐3‐aza‐10‐oxatricyclo[5.2.1.0^1,5]dec‐8‐enes.     

New Optically Active 2H‐Azirin‐3‐amines as Synthons for Enantiomerically Pure 2,2‐Disubstituted Glycines: Synthesis of Synthons for Tyr(2Me) and Dopa(2Me), and Their Incorporation into Dipeptides

The synthesis of novel unsymmetrically 2,2‐disubstituted 2H‐azirin‐3‐amines with chiral auxiliary amino groups is described. Chromatographic separation of the mixture of diastereoisomers yielded (1′R,2S)‐ 2a , b and (1′R,2R)‐ 2a , b (c.f. Scheme 1 and Table 1), which are synthons for (S)‐ and (R)‐2‐methyltyrosine and 2‐methyl‐3′,4′‐dihydroxyphenylalanine. Another new synthon 2c , i.e., a synthon for 2‐(azidomethyl)alanine, was prepared but could not be separated into its pure diastereoisomers. The reaction of 2 with thiobenzoic acid, benzoic acid, and the amino acid Fmoc‐Val‐OH yielded the monothiodiamides 11 , the diamides 12 (cf. Scheme 3 and Table 3), and the dipeptides 13 (cf. Scheme 4 and Table 4), respectively. From 13 , each protecting group was removed selectively under standard conditions (cf. Schemes 5–7 and Tables 5–6). The configuration at C(2) of the amino acid derivatives (1R,1′R)‐ 11a , (1R,1′R)‐ 11b , (1S,1′R)‐ 12b , and (1R,1′R)‐ 12b was determined by X‐ray crystallography relative to the known configuration of the chiral auxiliary group.     

Metabolism of Deuterated threo‐Dihydroxy Fatty Acids in Saccharomyces cerevisiae: Enantioselective Formation and Characterization of Hydroxylactones and γ‐Lactones

Biotransformation of (±)‐threo‐7,8‐dihydroxy(7,8‐²H₂)tetradecanoic acids (threo‐(7,8‐²H₂)‐ 3 ) in Saccharomyces cerevisiae afforded 5,6‐dihydroxy(5,6‐²H₂)dodecanoic acids (threo‐(5,6‐²H₂)‐ 4 ), which were converted to (5S,6S)‐6‐hydroxy(5,6‐²H₂)dodecano‐5‐lactone ((5S,6S)‐(5,6‐²H₂)‐ 7 ) with 80% e.e. and (5S,6S)‐5‐hydroxy(5,6‐²H₂)dodecano‐6‐lactone ((5S,6S)‐5,6‐²H₂)‐ 8 ). Further β‐oxidation of threo‐(5,6‐²H₂)‐ 4 yielded 3,4‐dihydroxy(3,4‐²H₂)decanoic acids (threo‐(3,4‐²H₂)‐ 5 ), which were converted to (3R,4R)‐3‐hydroxy(3,4‐²H₂)decano‐4‐lactone ((3R,4R)‐ 9 ) with 44% e.e. and converted to ²H‐labeled decano‐4‐lactones ((4R)‐(3‐²H₁)‐ and (4R)‐(2,3‐²H₂)‐ 6 ) with 96% e.e. These results were confirmed by experiments in which (±)‐threo‐3,4‐dihydroxy(3,4‐²H₂)decanoic acids (threo‐(3,4‐²H₂)‐ 5 ) were incubated with yeast. From incubations of methyl (5S,6S)‐ and (5R,6R)‐5,6‐dihydroxy(5,6‐²H₂)dodecanoates ((5S,6S)‐ and (5R,6R)‐(5,6‐²H₂)‐ 4a ), the (5S,6S)‐enantiomer was identified as the precursor of (4R)‐(3‐²H₁)‐ and (2,3‐²H₂)‐ 6 ). Therefore, (4R)‐ 6 is synthesized from (3S,4S)‐ 5 by an oxidation/keto acid reduction pathway involving hydrogen transfer from C(4) to C(2). In an analogous experiment, methyl (9S,10S)‐9,10‐dihydroxyoctadecanoate ((9S,10S)‐ 10a ) was metabolized to (3S,4S)‐3,4‐dihydroxydodecanoic acid ((3S,4S)‐ 15 ) and converted to (4R)‐dodecano‐4‐lactone ((4R)‐ 18 ).     

Synthesis of Substituted Tricyclo[5.3.1.04,9]undecan‐2,6‐dione from 4,4‐Disubstituted Cyclohexanone Enamines and Methacryloyl Chloride

Morpholine enamines 4‐acetyl‐4‐methyl‐1‐morpholinocyclohexene 4a, 4‐acetyl‐4‐phenyl‐1‐morpholinocyclohexene 4b, and 4‐acetyl‐4‐isopropenyl‐1‐morpholinocyclohexene 4c react with methacryloyl chloride to give 1,7‐dimethyl‐4(N‐morpholino) tricyclo[5.3.1.0^4,9]undecan‐2,6‐dione 9a , 1‐phenyl‐7‐methyl‐4(N‐morpholino) tricyclo[5.3.1.0^4,9]undecan‐2,6‐dione 9b , and 1‐ispropenyl‐7‐methyl‐4(N‐morpholino) tricyclo[5.3.1.0^4,9]undecan‐2,6‐dione 9c respectively, along with the corresponding substituted adamandane‐2,4‐diones.