Microwave-assisted tandem Wittig–intramolecular Diels–Alder cycloaddition. Product distribution and stereochemical assignment

Wu, Jing; Sun, Lijie; Dai, Wei‐Min

doi:10.1016/j.tet.2006.06.039

Cited by 34 publications

(46 citation statements)

References 105 publications

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“…6 In order to accurately analyze the stereoselectivity of the IMDA reaction, we checked the crude reaction mixtures by 1 H NMR spectroscopy as we had done in our early studies. 3,4 In contrast to the reported result that 5a formed a single cis-adduct 7a in 80% yield, 6 we recognized three cycloadducts in the 1 H NMR spectrum of the reaction mixture and obtained, after column chromatographic purification, the products 7a (74%), 8a (6%), and 9a (9%) in a combined yield of 89% (Table 1, entry 1). The IMDA reaction of 5b was reported to be quite sluggish, and silica gel was used to promote full conversion after 20 hours at 90 °C, afford-R…”

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confidence: 85%

“…90:10 to 100:0) which may be slightly deteriorated upon introduction of the C1 or/and C10 substituents (R 1 ,R 3 ≠ H in 3); and (c) microwave heating at higher temperatures does not significantly decrease stereoselectivity of IMDA reaction of 3 as compared to thermal heating, which is consistent with our early findings in the related process. 3,4 Therefore, by designing suitable precursors, IMDA reaction of the hydroxamate-tethered 1,3,9-decatrienes is capable of forming highly functionalized adducts in excellent stereoselectivity, 6,11 and the 3H-benzo[d] [1,2]oxazin-4-one derivatives 4 12 should be useful for general organic synthesis.…”

Section: Figurementioning

confidence: 99%

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Stereoselectivity of Intramolecular Diels-Alder Reaction of Hydroxamate-Tethered 1,3,9-Decatrienes under Thermal and Microwave Heating

Wang¹,

Wu²,

Dai³

2009

Synlett

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Intramolecular Diels-Alder (IMDA) reaction of the hydroxamate-tethered 1,3,9-decatrienes has been investigated under both thermal and microwave heating, and the stereoselectivity has been revisited. It was found that a temperature-dependent rearrangement of (2E,4E)-hexadien-1-yl N-benzylhydroxamates into the corresponding (2E,4)-1-methylpentadien-1-yl derivatives took place prior to IMDA reaction upon heating, and up to four cycloadducts were identified by analysis of the crude reaction mixtures. The IMDA reaction could be accelerated with microwave irradiation at 180 °C in MeCN. Stereoselectivity of the microwave-assisted IMDA reaction has been examined by using the substituents appended at C1, C5, and C10 of the hydroxamate-tethered 1,3,9-decatrienes.In our previous studies on microwave-assisted intramolecular Diels-Alder (IMDA) reaction 1,2 of the ester-tethered 1,3,8-nonatrienes 1 (Figure 1) we confirmed that the cycloaddition could be significantly accelerated with microwave irradiation at 180 °C in MeCN as compared to thermal heating at 100-110 °C in PhMe while the stereoselectivity remained the same, that is, in the range of ca. 70:30 in favor of the trans-bicyclic adducts. 3 Under the same microwave-heating conditions, the sorbate-derived 1,3,8-nonatrienes 2 gave slightly higher stereoselectivity of ca. 90:10, 4 being consistent with the result observed for the thermal reaction. 5 But we discovered that the initially formed major trans-adducts underwent epimerization during the cycloaddition and upon exposure to silica gel, resulting in isolation of two cis-bicyclic adducts. 4 In searching for a different class of substrates for IMDA reaction with better stereoselectivity, we became interested in the hydroxamate-tethered 1,3,9-decatrienes 3 (Figure 1). The examples of compound 3 were first reported by Ishikawa and Saito's group in 2001. 6 It was claimed that a single diastereomer of 4 was formed from 3 (R 1 = Me, R 2 = R 3 = H). An explanation on the stereoselectivity was offered by considering an entropically favored process as the result of close proximity among the diene and dienophile moieties in the most stable conformation of 3. Therefore, the high stereoselectivity has been attributed to the hydroxamate tether effect on IMDA reaction as compared to the corresponding ester-and amidetethered substrates. 6-8 We were assuming that IMDA reaction of 3 should be accelerated under microwave heating to form adducts 4 with improved efficiency while the stereoselectivity observed for the thermal reaction should not be deteriorated. Figure 1The ester-tethered 1,3,8-nonatrienes 1 and 2, and formation of 3H-benzo[d][1,2]oxazin-4-one derivatives 4 via intramolecular Diels-Alder reaction of the hydroxamate-tethered 1,3,9-decatrienes 3 Now we report here on our findings for the IMDA reaction of 3 under thermal and microwave heating along with the stereoselectivity as probed by the substituents at C1, C5, and C10 of the 1,3,9-decatrienes 3.We first re-examined the thermal reactions of the known substrates 5a,b at 80...

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confidence: 85%

Section: Figurementioning

confidence: 99%

Stereoselectivity of Intramolecular Diels-Alder Reaction of Hydroxamate-Tethered 1,3,9-Decatrienes under Thermal and Microwave Heating

Wang¹,

Wu²,

Dai³

2009

Synlett

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“…A typical such cycloaddition is [4+2]-cycloaddition, such as the classical Diels Alder reaction, which can be performed both inter- [69,124] and intramolecularly [125][126][127][128][129][130][131][132] in tandem with a Wittig-reaction.…”

Section: One-pot Wittig-and Hwe Olefination/cycloaddition Reactionmentioning

confidence: 99%

Tandem-, Domino- and One-Pot Reactions Involving Wittig- and Horner-Wadsworth-Emmons Olefination

Merza¹,

Taha²,

Thiemann³

2018

Alkenes

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The Wittig olefination utilizing phosphoranes and the related Horner-WadsworthEmmons (HWE) reaction using phosphonates transform aldehydes and ketones into substituted alkenes. Because of the versatility of the reactions and the compatibility of many functional groups towards the transformations, both Wittig olefination and HWE reactions are a mainstay in the arsenal of organic synthesis. Here, an overview is given on Wittig-and Horner-Wadsworth-Emmons (HWE) reactions run in combination with other transformations in one-pot procedures. The focus lies on one-pot oxidation Wittig/HWE protocols, Wittig/HWE olefinations run in concert with metal catalyzed cross-coupling reactions, Domino Wittig/HWE-cycloaddition and Wittig-Michael transformations.

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“…Three consecutive carbon-carbon bonds in the end product were formed rapidly during this tandem process under the microwave irradiation efficiently. Wu et al (2006) achieved 90-99% yield in the intramolecular Diels-Alder cycloaddition of different esters tethered 1,3,8-nonatrienes under controlled microwave heating.…”

Section: Diels-alder Additionmentioning

confidence: 99%

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2014

Microwave-Assisted Organic Synthesis

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Microwave-assisted tandem Wittig–intramolecular Diels–Alder cycloaddition. Product distribution and stereochemical assignment

Cited by 34 publications

References 105 publications

Stereoselectivity of Intramolecular Diels-Alder Reaction of Hydroxamate-Tethered 1,3,9-Decatrienes under Thermal and Microwave Heating

Stereoselectivity of Intramolecular Diels-Alder Reaction of Hydroxamate-Tethered 1,3,9-Decatrienes under Thermal and Microwave Heating

Tandem-, Domino- and One-Pot Reactions Involving Wittig- and Horner-Wadsworth-Emmons Olefination

Elimination

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