Total Synthesis of (+)‐Machaeriol D with a Key Regio‐ and Stereoselective S<sub>N</sub>2′ Reaction

Wang, Qiaoling; Huang, Qinggang; Chen, Bin; Lu, Jiangping; Wang, Hui; She, Xuegong; Pan, Xinfu

doi:10.1002/ange.200600006

Cited by 11 publications

(6 citation statements)

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“…Thus, the reaction of PyDipSi‐arene 4c with phenylacetylene using the PdCl 2 (dppf)/AgF catalytic system, previously developed for the alkynylation of aryltrimethoxysilanes,36 allowed for the formation of the alkynylated cross‐coupling product 24 in 91% yield. A subsequent saponification/cyclization cascade37 afforded benzofuran derivative 25 in 72% yield (Scheme ). The overall four‐step sequence, including the installation of the PyDipSi group and the Pd‐catalyzed ortho ‐acetoxylation reaction, constitutes a powerful strategy for the synthesis of the polysubstituted benzofuran core from simple haloarenes.…”

Section: Resultsmentioning

confidence: 99%

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

et al. 2011

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A novel, easily removable and modifiable silicon-tethered pyridyldiisopropylsilyl directing group for C–H functionalizations of arenes has been developed. The installation of the pyridyldiisopropylsilyl group can efficiently be achieved via two complementary routes using easily available 2-(diisopropylsilyl)pyridine (5). The first strategy features a nucleophilic hydride substitution at the silicon atom in 5 with aryllithium reagents generated in situ from the corresponding aryl bromides or iodides. The second milder route exploits a highly efficient room-temperature rhodium(I)-catalyzed cross-coupling reaction between 5 and aryl iodides. The latter approach can be applied to the preparation of a wide range of pyridyldiisopropylsilyl-substituted arenes possessing a variety of functional groups, including those incompatible with organometallic reagents. The pyridyldiisopropylsilyl directing group allows for a highly efficient, regioselective palladium(II)-catalyzed mono-ortho-acyloxylation and ortho-halogenation of various aromatic compounds. Most impor-tantly, the silicon-tethered directing group in both acyloxylated and halogenated products can easily be removed or efficiently converted into an array of other valuable functionalities. These transformations include protio-, deuterio-, halo-, boro-, and alkynyldesilylations, as well as a conversion of the directing group into the hydroxy functionality. In addition, the construction of aryl-aryl bonds via the Hiyama–Denmark cross-coupling reaction is feasible for the acetoxylated products. Moreover, the ortho-halogenated pyridyldiisopropylsilylarenes, bearing both nucleophilic pyridyldiisopropylsilyl and electrophilic aryl halide moieties, represent synthetically attractive 1,2-ambiphiles. A unique reactivity of these ambiphiles has been demonstrated in efficient syntheses of arylenediyne and benzosilole derivatives, as well as in a facile generation of benzyne. In addition, preliminary mechanistic studies of the acyloxylation and halogenation reactions have been performed. A trinuclear palladacycle intermediate has been isolated from a stoichiometric reaction between diisopropyl-(phenyl)pyrid-2-ylsilane (3a) and palladium acetate. Furthermore, both C–H functionalization reactions exhibited equally high values of the intramolecular primary kinetic isotope effect (kH/kD = 6.7). Based on these observations, a general mechanism involving the formation of a palladacycle via a C–H activation process as the rate-determining step has been proposed.

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Section: Resultsmentioning

confidence: 99%

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

et al. 2011

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“…To this end, we fitted and compared two different models of trait evolution. First, we fitted a single-rate multivariate Brownian Motion (BM) model that corresponds to a random Garver et al, 1976;Yasuda et al, 1979;Wang et al, 2006;Takita et al, 2011) , responses to a specific compound) were calculated using the "fitContinuous" function, which we compared using the corrected Akaike information criterion (AICc). Lower AICc values (AICc ≤ 10) thereby indicate better evidence for a given model.…”

Section: Phylogenetic Analysesmentioning

confidence: 99%

Unraveling the Olfactory Biases of Male Euglossine Bees: Species-Specific Antennal Responses and Their Evolutionary Significance for Perfume Flowers

et al. 2021

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Male euglossine bees exhibit unique adaptations for the acquisition and accumulation of chemical compounds from “perfume flowers” and other sources. During courtship display, male bees expose perfume mixtures, presumably to convey species-specific recognition and/or mate choice signals to females. Because olfaction regulates both signal production (in males) and signal detection (in females) in this communication system, strong selective pressures are expected to act on the olfactory system, which could lead to sensory specialization in favor of an increased sensitivity to specific chemical compounds. The floral scents of euglossine-pollinated plants are hypothesized to have evolved in response to the preexisting sensory biases of their male euglossine bee pollinators. However, this has never been investigated at the peripheral olfactory circuitry of distinct pollinating genera. Here, we present a comparative analysis using electroantennography (EAG) of males across the phylogeny of 29 euglossine bee species, among them Euglossa and Eulaema species. First, we tested whether antennal responses differ among different euglossine genera, subgenera and species. Secondly, we conducted a comparative phylogenetic analysis to investigate the macroevolutionary patterns of antennal responses across the euglossine bee phylogeny. We found that antennal response profiles are very unique on the species level and differ on the subgenus and the genus level. The differences can be explained by chemical compounds typically found in the floral scent bouquets of perfume flowers and specific compounds of species either pollinated by Euglossa (e.g., ipsdienol) or Eulaema bees (e.g., (−)-(E)-carvone epoxide). Also, we detected a phylogenetic signal in mean antennal responses and found that especially at the species level of our simulation the overall antennal responses exhibit greater disparity relative to a null model of pure Brownian-motion across the phylogeny. Altogether, our results suggest that (1) euglossine bee species exhibit species-specific antennal responses that differ among euglossine genera and subgenera, (2) antennal responses diverge early after speciation events, and (3) scent composition of perfume flowers evolved in response to pollinator-mediated selection imposed by preexisting sensory biases in euglossine bees.

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“…The preparation of the other required coupling partner, aldehyde 10, began with methyl ester 8, [11] which was converted into the corresponding bis-reversed prenylated ester 9 through a copper-catalyzed etherification [12] with 1,1-dimethylpropynyl carbonate and Lindlar hydrogenation (72 % overall yield). Chemoselective reduction of 9 with LiAlH 4 , followed by oxidation with DMP led to aldehyde 10 in 92 % overall yield for the two steps.…”

Section: Dedicated To Masakatsu Shibasaki On the Occasion Of His 60thmentioning

confidence: 99%

Cascade Reactions Involving Formal [2+2] Thermal Cycloadditions: Total Synthesis of Artochamins F, H, I, and J

Nicolaou¹,

Lister²,

Denton³

et al. 2007

Angew Chem Int Ed

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Dedicated to Masakatsu Shibasaki on the occasion of his 60th birthdayThe Artocarpus genus encompasses approximately 60 species of trees that are distributed throughout the tropical regions of Asia. Selected members of this family of plants have been used as traditional folk medicines in Sri Lanka, Taiwan, Thailand, and Indonesia. [1][2][3][4] A search for the bioactive ingredients of these plants led to the isolation of several bioactive prenylated flavanoids from the roots of Artocarpus chama, [5] and more recently a number of weakly cytotoxic prenylated stilbenes and their derivatives.[6] Artochamins F, H, I, and J (1-4, Scheme 1) are among the most structurally fascinating members of this group of compounds. Herein we describe the total synthesis of all four natural products through an expedient route that involves a cascade sequence featuring a novel formal [2+2] thermal cycloaddition reaction.The unique bicyclo[3.2.0]heptane carbon frameworks of artochamins H-J (2-4) would appear to be biogenetically derived from artochamin F (1), or a derivative thereof, through a formal [2+2] cycloaddition reaction between the stilbene alkene and one of the prenyl groups.[6] Furthermore, the racemic nature [7] of 2-4 could implicate a non-enzymatic process for this transformation, given the pairwise enantiotopic relationship between both the top and bottom faces of the two prenyl moieties. We were intrigued by the possibility of accomplishing the required cycloaddition under thermal conditions [8] since we speculated that the realization of such a reaction would lead to a concise synthetic approach to the artochamins from stilbenes 5 a and/or 5 b through a cascade sequence that involved, in addition to the key cyclobutaneforming process, two consecutive Claisen rearrangements. Furthermore, protecting-group design on the intermediates was expected to modulate the cascade reaction and allow selective pathways so as to deliver any of the four targeted natural products (1-4).The first objective was the stereoselective construction of an appropriately functionalized stilbene derivative from which the formal [2+2] cycloaddition reaction within the projected cascade could be investigated. The Julia-Kocienski olefination [9] was chosen [10] as the key step for this initial construction as shown in Scheme 2.Thus, the substituted phenyltetrazolesulfones 7 a and 7 b were prepared from 3,4-dihydroxybenzaldehyde (6) in a straightforward manner that involved protection (either as the corresponding Boc derivative or silyl ether), reduction with NaBH 4 , and Mitsunobu coupling with 1-phenyl-1H-tetrazole-5-thiol, followed by molybdenum-catalyzed oxidation of the resulting sulfides to the desired sulfones 7 a (73 % overall yield from 6) and 7 b (77 % overall yield from 6). The preparation of the other required coupling partner, aldehyde 10, began with methyl ester 8, [11] which was converted into the corresponding bis-reversed prenylated ester 9 through a copper-catalyzed etherification [12] with 1,1-dimethylpropynyl carbonate and Lindlar h...

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Total Synthesis of (+)‐Machaeriol D with a Key Regio‐ and Stereoselective S_N2′ Reaction

Cited by 11 publications

References 47 publications

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

Unraveling the Olfactory Biases of Male Euglossine Bees: Species-Specific Antennal Responses and Their Evolutionary Significance for Perfume Flowers

Cascade Reactions Involving Formal [2+2] Thermal Cycloadditions: Total Synthesis of Artochamins F, H, I, and J

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Total Synthesis of (+)‐Machaeriol D with a Key Regio‐ and Stereoselective SN2′ Reaction

Cited by 11 publications

References 47 publications

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

Unraveling the Olfactory Biases of Male Euglossine Bees: Species-Specific Antennal Responses and Their Evolutionary Significance for Perfume Flowers

Cascade Reactions Involving Formal [2+2] Thermal Cycloadditions: Total Synthesis of Artochamins F, H, I, and J

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Total Synthesis of (+)‐Machaeriol D with a Key Regio‐ and Stereoselective S_N2′ Reaction