- A mild method for the replacement of a hydroxyl group by halogen: 2. unified procedure and stereochemical studies
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N,N-Dimethyl- and N,N-diisopropyl-1-halo-2-methyl-l-propenylamines are readily available reagents for the mild deoxyhalogenation of alcohols and hydroxyacids. In this study we showed that the reactivity of the reagents can be tuned by varying the size of the alkyl groups on the reagents: the replacement of methyl by isopropyl groups led to a significant increase of reactivity. We then described a unified procedure for all deoxyhalogenations using the readily available α-chloroenamines as reagents with (bromination, iodination) or without (chlorination) an alkaline bromide or iodide. Finally, we showed that deoxyhalogenation reactions of secondary alcohols were highly stereospecific and generally occurred with inversion of configuration.
- Gati, Wafa,Munyemana, Fran?ois,Colens, Alain,Srour, Aladdin,Dufour, Mathilde,Vardhan Reddy, K. Harsha,Téchy, Brigitte,Rosse, Gérard,Schweiger, Ed,Qiao, Qi,Ghosez, Léon
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- Establishing Consensus Stereostructures for the Naphthoquinonopyrano-γ-lactone Natural Products (–)-Arizonin B1 and (–)-Arizonin C1 by Total Syntheses. Diastereocontrol of Oxa-Pictet–Spengler Cyclizations by Protective-Group Optimization
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Previous total syntheses of arizonin C1 (4) led to opposite assignments of its absolute configuration. Here, we report the fourth total synthesis thereof. In addition, we disclose the first total synthesis of arizonin B1 (3) proceeding differently than via arizonin C1. The stereocenters of the two targets stemmed from an asymmetric dihydroxylation and an ensuing oxa-Pictet–Spengler cyclization. Their configurations were in line with Fernandes' assignments. Protective-group variation in the substrate modulated the diastereoselectivity of the Pictet–Spengler cyclization between 77:23 in favor of a trans disubstitution at C-3a vs. C-5 – used for preparing the natural (–)-arizonins C1 and B1 – and 100:0 in favor of a cis disubstitution – exploited for synthesizing the unnatural (+)-5-epi-arizonins C1 and B1. All naphthalenes of the present study were derived from the (benzyloxy)methoxynaphthalenediol 19. It resulted from a Diels–Alder reaction of the aryne 17a with the siloxyfuran 18a.
- Neumeyer, Markus,Brückner, Reinhard
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p. 2512 - 2539
(2017/05/15)
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- Controlling the Substitution Pattern of Hexasubstituted Naphthalenes by Aryne/Siloxyfuran Diels–Alder Additions: Regio- and Stereocontrolled Synthesis of Arizonin C1 Analogs
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3,4-Dimethoxybenz-1-yne and 2-siloxylated furans without or with a bromine atom at C-3 undergo Diels–Alder reactions with orientational selectivity. Hydrolysis furnished a bromine-free or a bromine-containing naphthalene, respectively. Bromination of the former provided a regioisomer of the latter. Either of the two compounds was processed to give a variety of unnatural naphthoquinonopyrano-γ-lactones. This occurred by a succession of (1) Heck coupling, (2) asymmetric dihydroxylation, (3) oxa-Pictet–Spengler cyclization, and (4) oxidation. The fifteen monomeric naphthoquinonopyrano-γ-lactone structures that we prepared resemble the natural product (–)-arizonin C1 or its C-5 epimer. Accordingly, they represent hexasubstituted naphthalenes likewise. The sixteenth naphthoquinonopyrano-γ-lactone that we synthesized is a kind of dimer. Its moieties are bridged differently than those in naturally occurring naphthoquinonopyrano-γ-lactone dimers.
- Neumeyer, Markus,Kopp, Julia,Brückner, Reinhard
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p. 2883 - 2915
(2017/06/06)
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- Comparison of the relative reactivities of the triisopropylsilyl group with two fluorous analogs
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The relative stabilities of two fluorous analogs, diisopropyl(3,3,4,4,5,5, 6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)silyl and diisopropyl-(4,4,5,5,6, 6,7,7,8,8,9,9,10,10,11,11,11-heptadeca-fluoroundecyl)silyl [C8F 17(CH2)nSi(i-Pr)2, where n = 2 or 3], of the standard triisopropylsilyl (TIPS) group are compared in the setting of alcohol protection. The fluorous silyl groups can be installed under standard conditions in comparable yields to the TIPS group, but the derived fluorous silyl ethers are more labile than TIPS ethers towards cleavage by both acids and fluoride.
- Sancho, Amador Garcia,Wang, Xiao,Sui, Bin,Curran, Dennis P.
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experimental part
p. 1035 - 1040
(2009/12/05)
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- Process for producing novel naphthyridine derivatives
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A novel naphthyridine derivative showing high activity as a tachykinin receptor antagonist can be produced at high efficiency by reacting an acylating agent such as a carboxylic acid derivative with a compound represented by the formula (1): wherein R1, R2 and R3 represent independently a hydrogen atom, a lower alkyl group, a lower alkoxyl group, an aryl group, a heteroaryl group, an amino group, etc., and X1 and X2 represent respectively a halogen atom.
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- Improved preparation of N-trimethylsilylpyridinium triflate, N- triphenylsilylpyridinium triflate, N-triisopropylsilylpyridinium triflate and their use in silylating alcohols to silyl ethers
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N-Silylpyridinium triflates 1a-c have been prepared in excellent yield from the corresponding allyl silanes by reaction with triflic acid followed by pyridine. Compounds 1a-c were used to prepare silyl ethers from alcohols in generally high yield. A convenient procedure has been developed which enables the silylation of alcohols without an aqueous workup in the product isolation.
- Olah, George A.,Klumpp, Douglas A.
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p. 744 - 746
(2007/10/03)
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- CONSTRUCTION OF FOUR CONSECUTIVE ASYMMETRIC CENTERS I. ANTI- AND SYN-SELECTIVE EPOXIDATION OF β-METHYL-CIS-HOMOALLYLIC ALCOHOLS
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All the diastereomers of 2,3-cis-epoxy-4-methyl-5-decanol and of 8,9-cis-epoxy-7-methyl-6-tridecanol were stereoselectively synthesized as key intermadiates in a model approach toward the stereoselective construction of four consecutive asymmetric centers.
- Hanamoto, Takeshi,Katsuki, Tsutomu,Yamaguchi, Masaru
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p. 6191 - 6194
(2007/10/02)
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- STUDIES WITH TRIALKYLSILYLTRIFLATES: NEW SYNTHESES AND APPLICATIONS
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Syntheses and applications are described for three useful reagents for silylation of unreactive substrates, tert-butyldimethylsilyl, triisopropylsilyl, and octadecyldimethylsilyl triflate.
- Corey, E. J.,Cho, Hidetsura,Ruecker, Christoph,Hua, Duy H.
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p. 3455 - 3458
(2007/10/02)
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