- Asymmetric total syntheses of rhynchophylline and isorhynchophylline
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The asymmetric total syntheses of (-)-rhynchophylline and (+)-isorhynchophylline were achieved in 17 and 16 steps, respectively, from butanal and ethyl acrylate. Our synthesis features Carreira ring expansion to construct the tetracyclic spirooxindole core in high diastereoselectivity and the use of Bosch's chiral lactam for preparation of enantioenriched cyclic imine.
- Zhang, Zhihong,Zhang, Wei,Kang, Fangyuan,Ip, Fanny C. F.,Ip, Nancy Y.,Tong, Rongbiao
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- Synthetic noribogaine
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Synthetic noribogaine preferably free of ibogaine and, optionally, one or more of other naturally occurring Tabernanth iboga alkaloids, is provided.
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Page/Page column 6
(2017/05/02)
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- Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone A
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Several approaches to the synthesis of ebelactone A 2 are described, culminating in the synthesis of the benzenesulfonate of 2-epi-ebelactone A 161. All the approaches were based on three fragments A, B and C, originally defined in general terms in Scheme 1, but eventually used as the aldehyde 72, the allenylsilane 3 and the aldehyde 139, respectively. They were joined, first B with C, and then B+C with A. In the main routes to fragments A and C, the relative stereochemistry was controlled by highly stereoselective enolate methylations 66 → 67, 68 → 69, and 135 → 136, in each case anti to an adjacent silyl group, and by a highly stereoselective hydroboration of an allylsilane 137 → 138, also anti to the silyl group. The hydroxyl groups destined to be on C-3 and C-11 were unmasked by silyl-to-hydroxy conversions 69 → 70 and 138 → 139 with retention of configuration. The stereochemistry created in the coupling of fragment B to C was controlled by the stereospecifically anti SE2′ reaction between the enantiomerically enriched allenylsilane 3 and the aldehyde 139. The double bond geometry was controlled by syn stereospecific silylcupration 148 → 151, and preserved by iododesilylation 151 → 152 of the vinylsilane with retention of configuration, and Nozaki-Hiyama-Kishi coupling with the aldehyde 72 gave the whole carbon skeleton 153 of ebelactone A with the correct relative configuration, all of which had been controlled by organosilicon chemistry. In the steps to remove the superfluous allylic hydroxyl, an intermediate allyllithium species 156 abstracted the proton on C-2, and its reprotonation inverted the configuration at that atom. Other routes to the fragments A and C were also explored, both successful and unsuccessful, both silicon-based and conventional, and a number of unexpected side reactions were investigated.
- Archibald, Sarah C.,Barden, David J.,Bazin, Jerome F.Y.,Fleming, Ian,Foster, Colin F.,Mandal, Ajay K.,Mandal, Amit K.,Parker, David,Takaki, Ken,Ware, Anne C.,Williams, Anne R.B.,Zwicky, Anna B.
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p. 1051 - 1064
(2007/10/03)
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- Synthesis of Talaromycins A, B, C, and E
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The synthesis of 2,2-diethyl-5-ethynyl-1,3-dioxane (9) is reported in an overall yield of 27percent from diethyl malonate.Addition of 5-ethyl tetrahydropyran-2-one to the lithium anion of (9) gave the hydroxy ketoacetylene (10) which was converted in four steps to the olefinic spiroacetals (19) and (20), which were obtained in a ratio of 2:1.The individual olefinic spiroacetals (19) and (20) gave access to the (+/-)-talomycins A and C, and B and E via a chlorohydration, reductive dechlorination, and deprotection sequence.
- Baker, Raymond,Boyes, Alastairs L.,Swain, Christopher J.
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p. 1415 - 1421
(2007/10/02)
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- Nucleophile-Catalysed Additions of Aldehydes and Ketones to Acrylic Compounds: The Effectiveness of High Pressures
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The preparation of a wide range of compounds of general type: CH2=C(Z)-CR1R2OH (Z = CN, COOR, CHO,; R1,R2 = H, alkyl, aryl) from the reaction of CH2=CHZ with aldehydes and ketones, is effectively catalysed by tertiary amines especially DABCO.Rates are found to be very strongly accelerated by high pressures (2-10 kbar) which alone permits the additions of ketones or of crotonic acid derivatives to take place.In the absence of carbonyl acceptors novel oligomers of acrylic compounds form.
- Hill, Jon S.,Isaacs, Neil S.
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p. 2641 - 2676
(2007/10/02)
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- SYNTHESIS AND 1H NMR STUDY OF 3,4-DIETHYL-1,2,3,3A,4,5-HEXAHYDRO-CANTHINONE-6
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The racemic mixtures of the two epimers of 3,4-diethyl-1,2,3,3a,4,5-hexahydro-canthinone-6 have been prepared.They were separated by crystallization of one of the synthesis intermediates.Identification of the configuration was possible by 1H NMR spectroscopy after running a 2D J-resolved spectrum of the "cis"-isomer.
- Bruyn, Andre De,Eeckhaut, Guy,Villaneuva, Juan,Hannart, Jean
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p. 5553 - 5562
(2007/10/02)
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- Synthesis of Vinca Alkaloids and Related Compounds, XIII. Syntheses Starting from 2-(Ethoxycarbonyl)tryptamine
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The Pictet-Spengler reaction of 2-(ethoxycarbonyl)tryptamine (1) with aldehyde esters 2 and 3 leads to unexpected products (4a and 9a/10a, resp.).The structures of the new compounds were elucidated by spectroscopic and chemical means.
- Kalaus, Gyoergy,Gyoery, Peter,Kajtar-Peredy, Maria,Radics, Lajos,Szabo, Lajos,Szantay, Csaba
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p. 1476 - 1483
(2007/10/02)
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