Povarov Reaction of Glyoxylate Imines Derived from 12-Aminodehydroabietic Acid

Glyoxylate and arylglyoxal imines based on 12-aminodehydroabietic acid undergo hetero-Diels—Alder (Povarov) reaction with ethyl vinyl ether, cyclopentadiene, and indene to give, respectively, methyl (8aR,9R,12aS)-3-aroyl-5-isopropyl–9,12a-dimethyl–7,8,8a,9,10,11,12,12a-octahydronaphtho[1,2-f]quinoline-9-carboxylates, methyl (7R,10aS,10dR,13aS)-1-aroyl–3-isopropyl–7,10a-dimethyl–2,5,6,6a,7,8,9,10,10a,10d,13,13a-dodecahydro-1H-naphtho[1,2-f]cyclopenta[c]quinoline-7-carboxylates, and methyl (6aS,11bS,11eS,15R,15aR)-6-aroyl–4-isopropyl–11e,15-dimethyl–2,5,6,6a,7,11b,11e,12,13,14,15,15a-1H-dodecahydroindeno[2,1-c]-naphtho[1,2-f]quinoline-15-carboxylates.     

Enantioselective syntheses of isoprostane and iridoid lactones intermediates by enzymatic transesterification

Crude Pseudomonas cepacia lipase (Amano PS-30) is a suitable biocatalyst for the kinetic resolution of the 1,2-cis-disubstituted cyclopentanoid building block (3aR*,4R*,6aS*)-(±)-4-hydroxymethyl-3,3a,4,6a-tetrahydrocyclopenta[b]furan-2-one through enantioselective transesterification. Enantiomerically enriched acetic acid (3aS,4S,6aR)-(+)-2-oxo-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-4-yl methyl ester was utilized in a formal synthesis of the iridoids (+)-isoiridomyrmecin and (−)-teucriumlactone.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Enantiomerically pure piperazines via NaBH4/I2 reduction of cyclic amides

Enantiomerically pure (3S,7R,8aS)-3-phenyloctahydropyrrolo[1,2-a]pyrazine-7-ol, (3S,7R,8aS)-3-methyl octahydropyrrolo[1,2-a]pyrazine-7-ol, (3S,7R,8aS)-3-isopropyloctahydropyrrolo[1,2-a]pyrazine-7-ol and (3S,7R,8aS)-3-isobutyloctahydropyrrolo[1,2-a]pyrazine-7-ol 16d were synthesized via preparation of the corresponding cyclic amides from enantiomerically pure l-proline and hydroxyproline derivatives followed by reduction using sodium borohydride-iodine.     

A convenient procedure for the synthesis of chiral 6,7-dihydroxy-1-phenylamino-dihydro-1H-pyrrolo[1,2-a]imidazole-2,5(3H,6H)-diones

The cyclocondensation reactions between l-α-amino acid phenylhydrazides and 2,3-O-isopropylidene-l-erythruronolactone in the presence of a catalytic amount of p-toluenesulfonic acid afforded diastereomerically pure (3S,6R,7R,7aS)-3-substituted-6,7-isopropylidenedioxy-1-phenylamino-dihydro-1H-pyrrolo[1,2-a]imidazole-2,5(3H,6H)-diones, which were converted by acidic hydrolysis with MeOH–HCl into their corresponding optically active (3S,6R,7R,7aS)-3-substituted-6,7-dihydroxy-1-phenylamino-dihydro-1H-pyrrolo[1,2-a]imidazole-2,5(3H,6H)-diones in good yields.     

A new strategy in enantioselective intramolecular hetero Diels-Alder reaction: catalytic double asymmetric induction during the tandem transetherification-intramolecular hetero Diels-Alder reaction of methyl (E)-4-methoxy-2-oxo-3-butenoate with rac-6-methyl-5-hepten-2-ol

An efficient catalytic double asymmetric induction during the tandem transetherification-intramolecular hetero Diels-Alder reaction has been developed. The enantioselective tandem reaction of methyl (E)-4-methoxy-2-oxo-3-butenoate with rac-6-methyl-5-hepten-2-ol has been achieved to provide methyl (2R,4aS,8aR)-3,4,4a,8a-tetrahydro-2,5,5-trimethyl-2H,5H-pyrano[4,3-b]-pyran-7-carboxylate in good yield with effective kinetic resolution (up to 95% selectivity), high diastereoselectivity (up to 92% de), and high enantioselectivity (up to 97% ee) in the presence of (S,S)-tert-Bu-bis(oxazoline)-Cu(SbF₆)₂ and 5 Å molecular sieves.     

New chiral block for cyclopentanoids synthesis

Hydroxymethylation of bicyclic allylsilane, (3aR,6R,6aS)-3,3a,6,6a-tetrahydro-6-(trimethylsilyl)-cyclopenta[c]furan-1-one with formaldehyde by Prins reaction proceeds via S_E2' mechanism with the formation of anti-addition product. Some reactions of obtained (3aS,4S,6aR)-4-(hydroxymethyl)-3,3a,4,6a-tetrahydro-1H-cyclopenta[c]furan-1-one were investigated.     

An efficient synthesis of (−)-3-deazaaristeromycin

The coupling reaction of 4-chloro-1H-imidazo[4,5-c]pyridine (6-chloro-3-deazapurine) and (3aS,4S,6R,6aR)-tetrahydro-2,2-dimethyl-6-vinyl-3aH-cyclopenta-[d][1,3]dioxo-4-ol under Mitsunobu reaction conditions provides, after three subsequent straightforward reactions, ready access to the highly biologically active (−)-3-deazaaristeromycin. The versatility of this procedure opens access to a diverse pool of 3-deazapurine carbocyclic nucleosides.     

Total synthesis of natural (+)-hyacinthacine A6 and non-natural (+)-7a-epi-hyacinthacine A1 and (+)-5,7a-diepi-hyacinthacine A6

Naturally occurring (1S,2R,3R,5R,7aR)-1,2-dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine [(+)-hyacinthacine A₆, 2] together with unnatural (1S,2R,3R,7aS)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine [(+)-7a-epi-hyacinthacine A₁, 3] and (1S,2R,3R,5S,7aS)-1,2-dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine [(+)-5,7a-diepi-hyacinthacine A₆, 4] have been synthesized from a DALDP derivative [5, (2R,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine], as the homochiral starting material. The synthetic process employed took advantages of Wittig methodology followed by internal lactamization, in the case of (+)-7a-epi-hyacinthacine A₁ (3), and reductive amination for (+)-hyacinthacine A₆ (2) and (+)-5,7a-diepi-hyacinthacine A₆ (4).     

Complementary kinetic and thermodynamic resolution of a chiral biaryl axis

The condensation of 2′-formylbiphenyl-2-carboxylic acid 4 with (S)-valinol proceeds under kinetic control to give a major product, (4bR,7S,aS)-6,7-dihydro-7-isopropyldibenz[c,e]oxazolo[3,2-a]azepin-9(4bH)-one 6a (84%), in which the biaryl axis has the (S)-configuration. Heating 6a at 140°C with a catalytic amount of acid gives rise to an equilibrium dominated by the diastereoisomeric (4bS,7S)-lactam 6b (6a:6b ratio 27:73), in which the biaryl unit has the (R)-configuration. The structures of both lactams were established by X-ray crystallography; no other diastereoisomers were obtained.     

Syntheses of pyridin-4-ylium chirons: applications in a synthesis of (+)-coniine

The compounds (3R,5S)-(+)-5-methyl-3-phenyl-2,3,5,6,7,8-hexahydro-oxazolo[3,2-a]pyridin-4-ylium iodide 4 and (3R,5S)-(+)-5-n-propyl-3-phenyl-2,3,5,6,7,8-hexahydro-oxazolo[3,2-a]pyridin-4-ylium iodide 5 were synthesized in two steps starting from the bicyclic thiolactam trans (3R,2aS)-(−)-5-thio-3-phenyl-2,3,6,7,8,2a-hexahydro-oxazolo[3,2-a]pyridine 1. In addition, starting from 5 an enantiospecific synthesis of (+)-coniine 7 was achieved.     

Highly diastereoselective approach to novel phenylindolizidinols via benzothieno analogues of tylophorine based on reductive desulfurization of benzo[b]thiophene

Chiral tetra- and hexahydro[1]benzothieno[2,3-f]indolizines 3–5, 9, and 11 were synthesized easily from benzo[b]thiophene-2-carboxaldehyde (1) and (S)-glutamic acid (2) in good overall yields and both high enantio- and diastereomeric purities. Applying a diastereoselective reductive desulfurization of benzo[b]thiophene followed by lactam reduction, epimeric alcohols 4a and 4b were readily converted into (7R or S,8aS)-phenylindolizidinols 6a,c. During these studies, the reduction of benzothienoindolizines 3–5, 9, 11, and 12, was investigated and the results obtained are also discussed.     

Stereocontrolled transformation of nitrohexofuranoses into cyclopentylamines via 2-oxabicyclo[2.2.1]heptanes. Part VI: Synthesis and incorporation of the novel polyhydroxylated 5-aminocyclopent-1-enecarboxylic acids into peptides

The first total synthesis of enantiopure methyl (3aR,4S,5S,6R,6aS)-4-benzyloxycarbonylamino-6-hydroxy-2,2-dimethyl-tetrahydro-3aH-cyclopenta[d][1,3]dioxole-5-carboxylate has been carried out according to our recent novel strategy for the transformation of nitrohexofuranoses into cyclopentylamines. This approach is based on an intramolecular cyclization that leads to 2-oxabicyclo[2.2.1]heptane derivatives. E1cb elimination of the methoxy substituent was observed when attempting to incorporate these β-amino acid into peptides. As a result, the synthesis and incorporation of the first polyhydroxylated 5-aminocyclopent-1-enecarboxylic acid into peptides were developed.     

Synthesis of (−)- and (+)-8-fluoro-galanthamine

The synthesis of racemic 8-fluorogalanthamine and its separation into (−)- and (+)-8-fluorogalanthamine (= (4aS,6R,8aS)- and (4aR,6S,8aR)-1-fluoro-4a,5,9,10,11,12-hexahydro-3-methoxy-11-methyl-6H-benzofuro[3a,3,2-ef][2]benzazepin-6-ol) is described.     

Three ginkgolide hydrates from Ginkgo biloba L.: ginkgolide A monohydrate,ginkgolide C sesquihydrate and ginkgolide J dihydrate,all determined at 120 K

A low‐temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐dimethylethyl)‐hexa­hydro‐4,7b‐di­hydroxy‐8‐methyl‐9H‐1,7a‐epoxymethano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclopenta­[1,2‐d]­furan‐5,9,12(4H)‐trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room‐temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b,11‐tetrahydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclopenta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b‐tri­hydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]furo[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five‐membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.     

Studies on the Michael addition of naphthoquinones to sugar nitro olefins: first synthesis of polyhydroxylated hexahydro-11H-benzo[a]carbazole-5,6-diones and hexahydro-11bH-benzo[b]carbazole-6,11-diones

A strategy for the synthesis of the novel (6bR,7R,8S,9S,10S,10aR)-8-(benzyloxy)-7,9,10-trihydroxy-6b,7,8,9,10,10a-hexahydro-11H-benzo[a]carbazole-5,6-dione is reported. The key steps were the Michael addition of 2-hydroxy-1,4-naphthoquinone to 1-nitrocyclohexene or 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-α-d-xylo-hex-5-enefuranose and the diastereoselective intramolecular Henry reaction of 3-O-benzyl-5,6-dideoxy-5-C-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-1,2-O-isopropylidene-6-nitro-α-d-glucofuranose to give the key (1S,2S,3S,4R,5R,6R)-3-(benzyloxy)-1,2,4-trihydroxy-5-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-6-nitrocyclohexane. When 2-hydroxy-1,4-naphthoquinone was replaced by (1,4-dimethoxynaphthalen-2-yl)lithium, the novel (1R,2S,3S,4R,4aS,11bS)-2-(benzyloxy)-1,3,4-trihydroxy-1,2,3,4,4a,5-hexahydro-11bH-benzo[b]carbazole-6,11-dione was obtained.     

Synthetic transformations of methylenelactones of eudesmanic type. Behavior of isoalantolactone under the conitions of heck reaction

By Heck reaction of isoalantolactone with aryl bromides or aryl iodides (3aR,4aS, 8aR,9aR,E)-3-arylmethylidene-8a-methyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-ones and (4aS,8aR,9aS)-3-arylmethyl-8a-methyl-5-methylidene-4a,5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-ones, products of the double bond shift, were synthesized. The yields of the arylation products depend on the nature of the catalytic system and on the structure of the aryl halide. The structures of (3aR,4aS,8aR,9aR,E)-3-(3,4-dimethoxybenzylidene)-8amethyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-one and (4aS,8aR,9aS)-3-(2-methylsulfanylbenzyl)-8amethyl-5-methylidene-4a,5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-one were proved by XRD analysis.     

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.     

Reactions of β-substituted amines-IV: Kinetics and stereochemistry of the thermal to (r) 3-chloro-1-ethylpiperidine,and the stereo-chemical course of their reactions with nucleophiles

The rate of the thermal rearrangement of (S) 2 chloromethyl-1-ethylpyrrolidine [(S)-1a] to (R)-3-chloro-1-ethylpiperidine [(R) 2a] has been examined at three temperatures in benzene by PMR and polarimetry. The rearrangement was shown to be completely stereospecific and to obey a simple first order rate law. The calculated E_a ΔH3 and ΔS3 were 22 ± 2 $\text{kcal}\text{mole}$ (25°), 21 ± 2.5 $\text{kcal}\text{mole}$ (25°) and - 10 ± 2 e.u. (0°K) respectively. The effect of solvents having differing dielectric constants was also studied. A transition state 9'a and an ion pair intermediate 3a are suggested for the rearrangement. The stereochemical course of the reactions of (S)-1a, (R)-2a and (S)-2a with hydroxide and methoxide ions have been shown to be 100% stereospecific with an uncertainty of about 1%. The absolute configurations of all optically active reactants and products [(S)- and (R)-4a, (S)-4b (R)- and (S)-5a, (R)-5b, (S,S')-6a, (S,R')-7a and (R,R')-8a] were established by chemical correlations with known compounds or by ORD and chemical inference. The ring opening of both the primary and secondary aziridinium ion positions of 1-azonia-1-ethylbicyclo [3.1.0]hexane [(S)-3a] by nucleophiles proceeds entirely by S_N2 processes. The conversion of (R)-1-ethyl-3-hydroxypiperidine [(R)-5a] to (S)-2a. HCl with thionyl chloride in chloroform proceeds by inversion with 4.8% racemization, whereas the thermal rearrangement of (S)-1a to (R)-2a occurs with complete retention of absolute configuration.     

New Lignan,Benzofuran, and Sesquiterpene Derivatives from the Roots of Leontopodium alpinum and L. leontopodioides

Three new compounds, including a benzofuran, 1‐{(2R*,3S*)‐3‐(β‐D ‐glucopyranosyloxy)‐2,3‐dihydro‐2‐[1‐(hydroxymethyl)vinyl]‐1‐benzofuran‐5‐yl}ethanone ( 1 ), a lignan, [(2S,3R,4R)‐4‐(3,4‐dimethoxybenzyl)‐2‐(3,4‐dimethoxyphenyl)tetrahydrofuran‐3‐yl]methyl (2E)‐2‐methylbut‐2‐enoate ( 2 ), and a silphiperfolene‐type sesquiterpene, [(1S,2Z,3aS,5aS,6R,8aR)‐1,3a,4,5,5a,6,7,8‐octahydro‐1,3a,6‐trimethylcyclopenta[c]pentalen‐2‐yl]methyl acetate ( 3 ), together with the known coumarins obliquin ( 4 ) and its 5‐methoxy derivative 5 were isolated from the roots of Leontopodium alpinum. Another known coumarin derivative, 5‐hydroxyobliquin ( 6 ), was isolated from the roots of L. leontopodioides. The structures of these compounds were established by spectroscopic studies.