Diastereoselective Formal Synthesis of the Antifungal Agent, (+)-Preussin. A New Entry to Chiral Pyrrolidines

Armas, Pedro de; García‐Tellado, Fernando; Marrero-Tellado, José Juan; Robles, Juana

doi:10.1016/s0040-4039(97)10468-3

Cited by 27 publications

(15 citation statements)

References 15 publications

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“…[7] This procedure was introduced by us in the formal synthesis of the antibiotic ()-preusin to install the C5 nonyl chain with the required R configuration (Scheme 2). [8] We hypothesized that the high Scheme 2. The formal stereoselective synthesis of ()-preusin.…”

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confidence: 99%

“…Here we present experimental evidence to confirm our initial hypothesis and establish the generality of this remarkable exo-facial template effect exercised by the 1,2-O-isopropylidene protecting group. [8] We prepared the structurally related 1,2-O-isoprolylideneprotected furanosides 1 a ± h [9] and carried out a systematic study of their allylation reactions (Table 1). Remarkably, 1,2-trans selectivity was achieved in all of the experiments carried out with BF 3´E t 2 O or TiCl 4 as the Lewis acid and allyltrimethylsilane as the nucleophile (Scheme 3; Table 2).…”

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confidence: 99%

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Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

García‐Tellado

Armas

Marrero-Tellado

2000

Angew. Chem. Int. Ed.

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Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

García‐Tellado

Armas

Marrero-Tellado

2000

Angew. Chem. Int. Ed.

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“…The β‐fragmentation of alkoxyl radicals is useful methodology to obtain a wide range of compounds such as olefins, halogenated compounds, medium‐ and large‐sized rings, and heterocycles 1,2. The β‐scission was the key step in the synthesis of bioactive natural products such as (–)‐CP‐263,1143a,3b the cytotoxic chondriamides A and C,3c and the antifungals deoxyvernolepin3d,3e and preussin 3f. The substrates for the scission step were alcohols or hemiacetals, which generated alkoxyl radicals on treatment with reagents1 such as (diacetoxyiodo)benzene (DIB) and iodine, HgO–iodine, or LTA.…”

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Synthesis of Alkaloid Analogues from β‐Amino Alcohols by β‐Fragmentation of Primary Alkoxyl Radicals

Boto¹,

Hernández²,

Hernández³

et al. 2006

Eur J Org Chem

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The fragmentation of primary alkoxyl radicals is usually a minor process with respect to hydrogen abstraction and other competing reactions. However, when β‐amino alcohols were used as substrates, the scission proceeded in good to excellent yields and no side reactions were observed. The fragmentation can be coupled with an allylation or alkylation reaction, to give alkaloid analogues and functionalized nitrogen heterocycles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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“…[4] Scheme 1. a) The postulated stereoelectronic model for reactions of substituted five-membered-ring oxocarbenium ions. [8] We hypothesized that the high Scheme 2. b) Schematic representation of the exo facial template effect exercised by the 1,2-O-isopropylidene protecting group.…”

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“…[8] We hypothesized that the high Scheme 2. [8] We prepared the structurally related 1,2-O-isoprolylideneprotected furanosides 1 a ± h [9] and carried out a systematic study of their allylation reactions (Table 1). The alkyl chain at C5 is introduced with the required R configuration by diastereoselective allylation of the bicyclic 1,2-O-isopropylidene-protected dihydroxypyrrolidine intermediate.…”

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Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

García‐Tellado¹,

Armas²,

Marrero-Tellado³

2000

Angewandte Chemie

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Dedicated to Professor Antonio GonzaÂlez on the occasion of his 83rd birthdayLewis acid mediated cleavage of chiral cyclic acetals is a useful synthetic tool for the asymmetric synthesis of CÀC bonds. [1] Specifically, one of the most widely used methods for the formation of C-glycosides involves a glycosidic acetal, a Lewis acid, and a carbon nucleophile. [2] The reaction proceeds via a cyclic oxocarbenium ion, which undergoes nucleophilic attack in a stereoelectronically controlled manner to provide the product with high stereoselectivity. [3±5] Conformational effects have been invoked to explain the stereoselective reactions of substituted five-membered-ring oxocarbenium ions (Scheme 1 a). [4] Scheme 1. a) The postulated stereoelectronic model for reactions of substituted five-membered-ring oxocarbenium ions. Nucleophilic attack occurs by a stereoelectronically controlled ªinside attackº on the lower energy conformer of the cation to provide the product in its lower energy form. b) Schematic representation of the exo facial template effect exercised by the 1,2-O-isopropylidene protecting group. The nucleophilic attack is directed by the acetal onto the exo face of the molecule to give the 1,2-trans product.Because of the biological and chemical importance of C-glycofuranosides, [2,6] we undertook a study of the Lewis acid promoted cleavage of 1,2-O-isopropylidene-protected glycofuranosides by allyltrimethylsilane as a feasible and stereoselective route to these structures. [7] This procedure was introduced by us in the formal synthesis of the antibiotic ()preusin to install the C5 nonyl chain with the required R configuration (Scheme 2). [8] We hypothesized that the high Scheme 2. The formal stereoselective synthesis of ()-preusin. The alkyl chain at C5 is introduced with the required R configuration by diastereoselective allylation of the bicyclic 1,2-O-isopropylidene-protected dihydroxypyrrolidine intermediate. PG protecting group. diastereoselectivity obtained in this experiment was due to the bicyclic nature of these acetals, which confers an intrinsic and general exo-facial bias to the incoming nucleophile, regardless of the other substituents on the heterocyclic ring (Scheme 1 b). If this were the case, then this template effect of the bicyclic acetal should be general for any 1,2-O-isopropylidene-protected glycofuranoside, and thus provide invariable 1,2-trans stereoselectivity for nucleophilic substitution at the anomeric center. Here we present experimental evidence to confirm our initial hypothesis and establish the generality of this remarkable exo-facial template effect exercised by the 1,2-O-isopropylidene protecting group. 152 ± 155.[10] For cyclopropanation of enones mediated by zinc and BF 3 , see I. Elphimoff-Felkin, P. Sadra, Tetrahedron 1975, 31, 2781 ± 2784 The following functional substrates were recovered under the standard reaction conditions (Table 1, entry 1) due to the mild nucleophilicity of the organochromium reagent: 1-dodecene (97 %), 1-dodecyne (93 %), 1-chlorododecane (91 %), e...

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Diastereoselective Formal Synthesis of the Antifungal Agent, (+)-Preussin. A New Entry to Chiral Pyrrolidines

Cited by 27 publications

References 15 publications

Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

Synthesis of Alkaloid Analogues from β‐Amino Alcohols by β‐Fragmentation of Primary Alkoxyl Radicals

Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

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