Saturated oxygen heterocycles

Elliott, Mark; Williams, Eve

doi:10.1039/b007290g

Cited by 122 publications

(16 citation statements)

References 224 publications

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“…The mixture is again heated to reflux until TLC (silica, n-hexane:MTBE 10:1) indicates full conversion. After cooling to ambient temperature the mixture is poured onto saturated NH 4 Cl solution, extracted three times with MTBE (20 mL each), washed with brine (15 mL) and dried over magnesium sulfate. After evaporation of the solvents under vacuum, the residue is purified by flash chromatography (silica, n-hexane:MTBE 15:1) to give 6a as a colourless liquid; yield: 1.13 g (5.84 mmol, 87 %).…”

Section: Alkylation Of Sodium Alkoxides (Williamson Ether Synthesis)mentioning

confidence: 99%

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

Schmidt

Nave

2007

Adv Synth Catal

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Enantiomerically pure 1,5-hexadiene-3,4-diol, derived from d-mannitol in a few steps, may serve as a starting material for enantiopure dihydropyrans and dihydrofurans bearing an unsaturated side chain which is amenable for further synthetic transformations. The synthesis relies on a ring sizeselective ring-closing metathesis reaction of a triene. Most likely, a catalyst-directing effect of an allylic hydroxy group is responsible for the selectivity.

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Section: Alkylation Of Sodium Alkoxides (Williamson Ether Synthesis)mentioning

confidence: 99%

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

Schmidt

Nave

2007

Adv Synth Catal

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“…As a consequence, a number of strategies have been employed for the stereoselective synthesis of tetrahydrofurans. [7][8][9] However, despite advances in synthetic methodology, highly substituted tetrahydrofurans remain difficult to access, and new approaches are needed. We now describe a new route to highly substituted tetrahydrofurans that proceeds with excellent diastereoselectivity, under mild conditions in a single step (Scheme 1) by a novel process initiated by metallocarbene O-H insertion but diverted by intramolecular aldol reaction.…”

Section: Introductionmentioning

confidence: 99%

Stereoselective Synthesis of Highly Substituted Tetrahydrofurans through Diverted Carbene OH Insertion Reaction

et al. 2015

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Abstract:Copper or rhodium catalyzed reaction of diazocarbonyl compounds with β-hydroxyketones gives highly substituted tetrahydrofurans with excellent diastereoselectivity, under mild conditions, in a single step process that starts as a carbene O-H insertion reaction but is diverted by an intramolecular aldol reaction.The tetrahydrofuran ring is a commonly found motif in naturally occurring bioactive compounds, and occurs in structural classes such as lignans, [1] acetogenins, [2] ionophores, [3] and macrolides. [4] Examples include (+)-fragransin A2 [5] and amphidinolide F [6] (Figure 1). As a consequence, a number of strategies have been employed for the stereoselective synthesis of tetrahydrofurans. [7][8][9] However, despite advances in synthetic methodology, highly substituted tetrahydrofurans remain difficult to access, and new approaches are needed. We now describe a new route to highly substituted tetrahydrofurans that proceeds with excellent diastereoselectivity, under mild conditions in a single step (Scheme 1) by a novel process initiated by metallocarbene O-H insertion but diverted by intramolecular aldol reaction.

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“…[3][4][5][6][7][8] The microtubule-stabilizing agent (Ϫ)-laulimalide, 9-18) also known as fijianolide B, which was isolated from several sponges (Cacospongia mycofijiensis,19) Hyattella sp., 20) Fasciospongia rimosa 21) ), contains 2,6-trans disubstituted 5,6-dihydro-2H-pyran as its C5-C9 portion. Stereoselective construction of thermodynamically less stable 2,6-trans substituted pyrans is one of most important subjects in synthesis of this attractive antitumor agent and its analogues.…”

mentioning

confidence: 99%

“…Homoallylic alcohol (4) was converted to diol by hydroboration-oxidation process with borane-tetrahydrofuran (THF) complex and subsequent treatment with hydrogen peroxide and sodium hydroxide. Then the resulting primary hydroxyl group was protected as a tert-butyldimethylsilyl (TBDMS) ether to give the secondary alcohol (5) in high yield. O-Allylation of 5 was troublesome.…”

mentioning

confidence: 99%

Stereoselective Synthesis of C3-C12 Dihydropyran Portion of Antitumor Laulimalide Using Copper-Catalyzed Oxonium Ylide Formation-[2,3] Shift

Yakura

Muramatsu

Uenishi

2005

CHEMICAL & PHARMACEUTICAL BULLETIN

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Tetrahydropyran and dihydropyran rings are structural components of a large number of natural products.1,2) Therefore, considerable attention has recently been directed toward their stereoselective synthesis. [3][4][5][6][7][8] The microtubule-stabilizing agent (Ϫ)-laulimalide, 9-18) also known as fijianolide B, which was isolated from several sponges (Cacospongia mycofijiensis,19) Hyattella sp., 20) Fasciospongia rimosa 21) ), contains 2,6-trans disubstituted 5,6-dihydro-2H-pyran as its C5-C9 portion. Stereoselective construction of thermodynamically less stable 2,6-trans substituted pyrans is one of most important subjects in synthesis of this attractive antitumor agent and its analogues.Metal catalyzed carbenoid reactions 22,23) have become a powerful tool for the synthesis of functionalized cyclic compounds including oxacycles. In 1994, Clark and co-workers reported that a copper-catalyzed reaction of 5-allyoxy-1-diazo-2-hexanone predominantly gave 2,6-trans-2-allyl-6-methy-3-dihydropyranone in good yield.24) This result stimulated us to investigate the metal catalyzed stereoselective synthesis of 2,6-trans disubstituted 3-pyranone (2) from adiazoketone (3) as a feasible method for synthesis of the C5-C9 portion of laulimalide and its analogues because 3 would be converted easily into the key intermediate (1) of the Mulzer's laulimalide synthesis, 11,25) as outlined in Chart 1. Herein, we describe the synthesis of 2 in high yield with excellent stereoselectivity by the copper-catalyzed oxonium ylide formation-[2,3] shift of 3 and conversion of 2 into 1 and its derivatives.a-Diazoketone (3) was prepared readily from the known alcohol (4) 11) as shown in Chart 2. Homoallylic alcohol (4) was converted to diol by hydroboration-oxidation process with borane-tetrahydrofuran (THF) complex and subsequent treatment with hydrogen peroxide and sodium hydroxide. Then the resulting primary hydroxyl group was protected as a tert-butyldimethylsilyl (TBDMS) ether to give the secondary alcohol (5) in high yield. O-Allylation of 5 was troublesome. Under usual allylation conditions, such as reaction with sodium hydride (NaH) and allyl bromide in THF, no reaction occurred. Several examinations revealed that treatment of 5 with NaH and allyl iodide in the presence of 15-crown-5 in THF at room temperature afforded allyl ether (6) in 96% yield. Deprotection of TBDMS group with tetrabutylammonium fluoride (TBAF), followed by two stepoxidation with Dess-Martin periodinane and oxone in dimethylformamide (DMF) 26) gave carboxylic acid (7) in 80% overall yield. Conversion of 7 into a-diazoketone (3) was achieved by the usual procedure, 27) formation of mixed acid anhydride with ethyl chloroformate and treatment with diazomethane, thereby providing 3 in 85% yield in two steps.With a-diazoketone (3) in hand, we turned our attention to cyclization of 3 by the metal catalyzed reaction (Eq. 1).(1)Formation of 2,6-disubstituted 3-pyranone using oxonium ylide formation-[2,3] shift of a-diazoketone has already been examined. Clark and co-worke...

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Saturated oxygen heterocycles

Cited by 122 publications

References 224 publications

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

Stereoselective Synthesis of Highly Substituted Tetrahydrofurans through Diverted Carbene OH Insertion Reaction

Stereoselective Synthesis of C3-C12 Dihydropyran Portion of Antitumor Laulimalide Using Copper-Catalyzed Oxonium Ylide Formation-[2,3] Shift

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