Doubly Diastereocontrolled Cyclization Based on Intramolecular Conjugate Addition Reactions Involving an Allylic Radical and an Anion

Tokoroyama, Takashi; Aoto, Takehiko

doi:10.1021/jo980188t

Cited by 14 publications

(6 citation statements)

References 19 publications

(46 reference statements)

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“…The synthesis of this aldehyde started from the monoprotected ethylene glycol [16] 3 which was converted into the iodide 4 (Scheme 3) by using a combination of iodine and triphenylphosphine. [17] Due to the somewhat unstable nature of 4, this compound was used immediately in a Weiler alkylation [18] of ethyl acetoacetate to provide the b-keto ester 5. Reduction of the keto group under Noyori conditions [19,20] with (R)-(+)-BINAP as the chirality inducer gave the b-hydroxyestor 6 in good yield and with good optical purity (82 %, 95 % ee).…”

Section: Resultsmentioning

confidence: 99%

“…R f = 0.78 (petroleum ether/diethyl ether, 1:1); [a] 15 (266 mg, 0.80 mmol), and 3 n NaOH (0.89 mL). The mixture was heated to 40 8C for 4 h, cooled to room temperature, and diluted with Et 2 O (20 mL) and brine (20 mL (Si(CH 3 ) 2 ), À4.4 (Si(CH 3 ) 2 ), 14.1 (CH 3 ), 18.0 (SiC), 25.3 (C-10), 25.8 (C (CH 3 ) 3 ), 32.8 (C-9), 35.6 (C-4), 36.1 (C-1), 36.4 (C-5), 37.7 (C-7), 52.0 (CO 2 CH 3 ), 55.1 (PMB CH 3 ), 55.6 (MOM CH 3 ) 55.7 (PhÀOCH 3 ), 69.4 (C-8), 70.2 (C-11), 72.3 (PMB CH 2 ), 78.3 (C-6), 95.6 (MOM CH 2 ), 108.6 (C-3'), 113.6 (PMB C-3,5), 121.5 (C-5'), 123.3 (C-1'), 129.1 (PMB C-2,6), 129.1 (C-2), 130.3 (C-4'), 130.6 (PMB C-1), 130.7 (C-3), 139.2 (C-6'), 156.3 (C-2'), 159.0 (PMB C-4), 168.5 ppm (CO 2 CH 3 ); IR (film): ñ = 1038, 1071, 1109, 1249, 1470, 1513, 1734, 2855, 2931, 2952 cm À1 ; MS (EI): m/z (%): 293 (2), 192 (5), 181 (10), 178 (10), 176 (10), 170 (17), 168 (12), 166 (16), 150 (16), 141 (17), 137 (47), 121 (100), 97 (14), 77 (8) (8 mL), and H 2 O (8 mL) was treated with LiOH·H 2 O (271 mg, 6.46 mmol) and stirred at 70 8C for 3 days. After being allowed to cool to room temperature, the reaction mixture was diluted with Et 2 O (20 mL) and water (50 mL).…”

Section: Ethyl 6-[(4-methoxybenzyl)oxy]-3-oxohexanoate (5)mentioning

confidence: 99%

“…The combined organic extracts were washed with saturated aqueous NaHCO 3 solution and dried over Na 2 SO 4 . After filtration and evaporation of the solvent, the crude product was chromatographed over silica gel to produce the b-keto ester 5 (8.59 1248, 1302, 1372, 1514, 1612, 1732, 2859, 2937, 3449 cm À1 ; MS (EI): m/z (%): 297 (10), 296 (17), 278 (22), 241 (8), 203 (9), 190 (12), 160 (11) 1096,1173,1204,1249,1302,1362,1464,1472,1514,1613,1737,2856,2930,2954 (8): DIBAL (1.0 m in hexane, 2.92 mL) was added dropwise to a stirred solution of ester 7 (1.00 g, 2.44 mmol) in dry CH 2 Cl 2 (25 mL) over 10 min at À78 8C. After the reaction had been stirred for 2 h at À78 8C, methanol (0.7 mL) was added, the cooling bath was removed, and the mixture was allowed to warm to room temperature.…”

Section: Ethyl 6-[(4-methoxybenzyl)oxy]-3-oxohexanoate (5)mentioning

confidence: 99%

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Total Synthesis of Salicylihalamides A and B

Herb

Bayer

Maier

2004

Chemistry A European J

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The paper illustrates two efficient routes to macrolactone 19 containing a 3-(para-methoxybenzyloxy)propyl side chain at C-15. The chiral center at C-15 was introduced by a Noyori reduction of keto ester 5. The intermediate common to both routes, aldehyde 8, was prepared from keto ester 5. The subsequent chain extension utilized Evans aldol reactions. The first route leads to the alkene 14, which was used, after hydroboration, for a Suzuki cross-coupling reaction with vinyl iodide 15. The derived seco acid 18 was converted into the macrolactone 19 by a Mitsunobu lactonization by using immobilized triphenylphosphine. Alternatively, an aldol reaction of 8 with the 4-pentenoyl derivative 20 was used to prepare alkene 26. This building block led to ester 28, which could also be converted into macrolactone 19 by the classical ring-closing metathesis. After conversion of the C-15 side chain to the corresponding aldehyde, the enamide was introduced through hemiaminal formation and formal elimination of water. Separation of the double-bond isomers and removal of the silyl protecting groups provided salicylihalamides A (E)-1 and B (Z)-1.

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Section: Resultsmentioning

confidence: 99%

Section: Ethyl 6-[(4-methoxybenzyl)oxy]-3-oxohexanoate (5)mentioning

confidence: 99%

Section: Ethyl 6-[(4-methoxybenzyl)oxy]-3-oxohexanoate (5)mentioning

confidence: 99%

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Total Synthesis of Salicylihalamides A and B

Herb

Bayer

Maier

2004

Chemistry A European J

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“…All kinds of electrophiles have been employed with these equivalents, − which have been used, for example, in the stereospecific total synthesis of cyclopentanoid antibiotics (±)-pentenomycins I−III ( 66 ), their epimers ( 67 ), and dehydropentenomycin I ( 68 ) via alcohol 65 40 as common synthetic precursor , (Scheme ). Also, α-bromoketal 69 can be lithiated and treated with propylene oxide affording alcohol 70 , which is transformed into enone 71 (Scheme ), an intermediate in the synthesis of the macrocyclic diterpenes (±)- epi -jatropone and (±)-jatropone …”

Section: B αβ-Unsaturated Protected Carbonyl Compoundsmentioning

confidence: 99%

Acylvinyl and Vinylogous Synthons

Chinchílla

Nájera

2000

Chem. Rev.

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“…With this in mind, radical and anionic versions of the highly diastereoselective cyclization 22 323 were investigated. [40] Treatment of (E)-allylic bromide 48 with tri-n-butyltin hydride gave a mixture of three diastereomeric cyclization products 49 a, 49 b, and 49 c in a ratio of 77:21:2 (Scheme 4). [41] of the TS in radical reactions [20] and indicates that the major strain factors present in the product might be considerably developed from a relatively early stage in the chain folding leading to TS.…”

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confidence: 99%

Diastereofacial Selection in Ring-Closure Reactions and Folding-Strain Stereocontrol

Tokoroyama¹

1998

Chem. Eur. J.

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Diastereoselective cyclization reactions are an effective means for the synthesis of cyclic natural products, since ring formation and construction of the diastereomeric centers are achieved at the same time. In fact cycloaddition reactions represented by the Diels ± Alder reaction are often highly stereoselective and have been extensively utilized in stereoselective syntheses.[1] In contrast, simple ring-closure reaction has attracted far less attention for this purpose, probably because of the view that marked diastereoselectivity could not be expected, since the transition state (TS) conformation could be more flexible than the TS in the cycloaddition reactions.[2] This is rather surprising, since effective diastereoselection in reactions involving cyclic intermediates or cyclic TSs are exemplified abundantly in connection with acyclic stereocontrol. [3] In ring-closure reactions, two types of diastereoselection are distinguished, namely simple diastereoselection and diastereofacial selection, [4] as in intermolecular cases [5,6] (Scheme 1). The former is concerned with the mutual Scheme 1. Two types of diastereoselection in ring-closure reactions.disposition of two diastereotopic reaction centers, and is regulated stereoelectronically and sterically. The problems associated with this type of stereoselection have been recently studied for aldol-type [5,6] or allylmetal reactions. [7,8] The latter type of diastereoselection represents the diastereodifferentiation of the newly forming bond relative to the stereogenic center present in the chain and has to do with a relative asymmetric induction. In the present article, the discussion is focused on this type of diastereocontrol, which is designated as folding-strain stereocontrol.[9±12] Whereas in the literature there are many instances of ring-closure reactions of various Diastereofacial Selection in Ring-Closure Reactions and Folding-Strain StereocontrolTakashi Tokoroyama* Abstract: The potential of diastereofacially selective ring-closure reactions in organic synthesis is advanced by the concept of folding-strain stereocontrol, that is, the use of the energy balance among diastereomeric foldings of an acyclic chain to determine the selectivity, which defines the difference from intermolecular reactions. For generalization of the concept, the diastereofacial selectivity and the factors affecting the folding strain have been investigated in cyclizations of two types of substrates with substituents at various positions on the acyclic chainsÐ2-(6'-trimethylsilylhex-4'-enyl)cyclohexene-2-ones and ethyl 7-bromo-2-methylhexanoates. Diastereoselectivity ranged from moderate to excellent, being subtly affected by the relative positions of a substituent to the forming bond. The conformational analysis of diastereomeric transition states is the central issue in the design of a diastereofacially selective ringclosure reaction. In addition, the effects on diastereofacial selectivity as regard substituent bulkiness, types of the reaction, and controlling substituents are di...

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Doubly Diastereocontrolled Cyclization Based on Intramolecular Conjugate Addition Reactions Involving an Allylic Radical and an Anion

Cited by 14 publications

References 19 publications

Total Synthesis of Salicylihalamides A and B

Total Synthesis of Salicylihalamides A and B

Acylvinyl and Vinylogous Synthons

Diastereofacial Selection in Ring-Closure Reactions and Folding-Strain Stereocontrol

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