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41.
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43.
Bhupendra P. Joshi 《Tetrahedron》2005,61(12):3075-3080
An ultrasound-assisted convenient method was developed for the conversion of toxic methoxylated cis-isomer of arylalkenes into its hypolipidemic active trans-isomer. Treatment of cis-isomer or mixture of all three isomers (1a-1j) with ammonium formate and 10% Pd/C gave arylalkanes (2a-2j), which upon oxidation with DDQ in anhydrous dioxane containing a little amount of silica gel, provided (E)-arylalkenes (3a-3g) in 42-72% yield depending upon the substituents attached at the aryl ring. The same method, upon addition of a few drops of water, provided hypolipidemic active arylalkanones (3h-3j) in 59-65% yield.  相似文献   
44.
Here, we present a remarkably mild and general initiation protocol for alkyl-radical generation from non-activated alkyl-iodides. An interaction between a silane and an alkyl iodide is excited by irradiation with visible light to trigger carbon–iodide bond homolysis and form the alkyl radical. We show how this method can be developed into an operationally simple and general Giese addition reaction that can tolerate a range of sensitive functionalities not normally explored in established approaches to this strategically important transformation. The new method requires no photocatalyst or other additives and uses only commerical tris(trimethylsilyl)silane and visible light to effectively combine a broad range of alkyl halides with activated alkenes to form C(sp3)–C(sp3) bonds embedded within complex frameworks.

Here, we present a remarkably mild and general initiation protocol for alkyl-radical generation from non-activated alkyl-iodides.

The efficient and straightforward construction of C(sp3)–C(sp3) bonds is a crucial process in organic synthesis. Over the past 80 years, the polar conjugate addition reaction has become a powerful method to forge a variety of C(sp3)–C(sp3) bonds.1 Alongside two-electron nucleophiles, alkyl-radicals – neutral yet nucleophilic species – have emerged as alternatives to organometallic reagents for additions to electron deficient alkenes.2 Since the 1960s, a variety of methods have been reported for the formation of alkyl-radicals; early examples include the decomposition of in situ generated organomercurial hydrides, the fragmentation of xanthate or Barton esters, or the UV-mediated homolysis of alkyl halides, amongst many others.3 Although these strategies tolerate a broad range of functionalities, the initiation processes can be complicated by the need for aggressive reaction conditions and frequently require toxic reagents such as tributyltin hydride, with notable exceptions.4,5The emergence of photoredox catalysis has obviated many of the potential drawbacks to the generation and use of alkyl-radicals. The exploitation of the multifaceted reactivity of visible light excited transition metal or organic-photocatalysts, whose properties can be tuned through modification of the ligand, metal and/or scaffold, facilitates optimization of the single electron transfer event towards alkyl-radical generation from a wide range of functionalized alkyl groups.6 In addition, the reactivity of electron donor–acceptor (EDA) complexes has also provided a straightforward means to form alkyl-radicals from a variety of precursors.7 As such, a plethora of methods have been developed for the generation of C(sp3)-centred radicals from a variety of commercially available native functionalities, which dramatically expand the scope of alkyl-radical chemistry. In this context, the single electron reduction of non-activated alkyl halides provides a useful means to generate alkyl radicals.8 As an example, Leonori and co-workers recently developed a method wherein halogen atom abstraction pathways were leveraged using radical species forged through photocatalyst-mediated oxidation event leading to a general alkyl-radical generation.9 Related to the current study, Jørgensen and co-workers published a visible-light mediated reduction of alkyl halides under very mild conditions. Accordingly, there remains a need for further innovation towards orthogonal, general and benign methods of alkyl-radical generation that tolerate a broad range of functionalities, thereby enabling the construction of a greater variety of C(sp3)–C(sp3) bonds.10Recently, we reported a general reaction to form tertiary alkylamines via the addition of alkyl-radicals (generated from non-activated alkyl-iodides) to in situ-generated all-alkyl iminium ions.11a This carbonyl alkylative amination (CAA) reaction was promoted by the action of blue LEDs and tris(trimethylsilyl)silane ((Me3Si)3Si–H). No photoredox catalyst is required. We believe that the alkyl-radical formation step, devoid of traditional initiating reagents, proceeds through the visible-light excitation of a transient ternary EDA complex, which stimulates homolysis of the carbon–iodide bond that would be otherwise stable under such irradiation conditions (Fig. 1B). The presence of an enamine was important to the initiation pathway, as revealed by an absorption band in the UV/vis spectrum of its mixture with an alkyl-iodide and (Me3Si)3Si–H.11a Gouverneur and co-workers have also reported an elegant example of visible-light mediated addition of more functionalized alkyl halides, such as iodofluoromethane, to electron deficient alkenes.12 They proposed that light mediated homolytic cleavage of iodofluoromethane was responsible for radical initiation prior to a classical chain process.Open in a separate windowFig. 1(A) Selected visible-light mediated methods for the generation of alkyl-radicals; (B) previous work – a method for tertiary amine formation exploiting a visible-light activation of a ternary EDA complex to promote alkyl-radical formation. (C) Previous work from Gouverneur & Gaunt labs on radical fluoromethylation. (D) This work – alkyl-radical formation promoted solely by visible light and tris-trimethylsilyl silane demonstrated through a remarkably practical and straightforward Giese reaction.Gouverneur et al. also showed methyl iodide was only efficient as a radical source under these conditions when an organic photocatalyst was present and the reaction of other simple non-activated alkyl iodides was only demonstrated in the presence of iodofluoromethane, which was presumably responsible for the initiation pathway (vide supra). Our prior work in this area also identified iodofluoromethane as a visible-light activated source of fluoromethyl radical and its addition to iminium ions and electron deficient alkenes (Fig. 1C).11b Taken together, these works reveal that the use of visible light and (Me3Si)3Si–H to initiate radical formation from non-activated alkyl halides has not been achieved in an unbiased transformation without the requirement of an initiation process via of the reaction components or a photocatalyst. Accordingly, we questioned whether a pathway mediated by visible-light and (Me3Si)3Si–H alone might facilitate alternative modes of radical initiation from non-activated alkyl halides, and therefore enable the general coupling of unbiased alkyl fragments with a wider range of acceptors under practical, straightforward reaction conditions.Herein, we report the successful realization of this idea through the development of a remarkably straightforward visible-light mediated method for alkyl-radical generation from non-activated alkyl iodides using only non-toxic tris(trimethylsilyl)silane as a reagent (Fig. 1D). While we are not certain of the precise pathway for the radical initiation, it seems likely that excitation of a species resulting from the interaction of tris(trimethylsilyl)silane and the alkyl iodide, leading to carbon–iodide bond homolysis. The utility of this activation mode is demonstrated through a broad and chemoselective Giese addition to electron deficient alkenes and is notable by its tolerance to a range of synthetically valuable functionalities in both alkyl iodide and alkene components. In comparison to other methods for Giese-addition,2,3,8,9,12 the conditions are mild and do not require expensive catalysts or cocktails of additives.Our studies were stimulated from an observation arising from the development of the visible light mediated carbonyl alkylative amination (shown in Fig. 1B). High yields of the tertiary amine product, arising from the union of alkyl-radical, aldehyde and secondary amine were maintained when using a 455 nm long-pass filter, which discounted UV-mediated carbon–iodide bond homolysis as the initiation pathway for alkyl-radical formation.11a To explore the formation of an alkyl-radical independently from the enamine component, the reaction conditions were simplified to comprise a representative alkyl halide and (Me3Si)3Si–H, which allowed us to first assess any impact solvent might have on the radical forming process. As shown in 13 However, 47% of 5 was still obtained after visible-light irradiation of a reaction mixture from which air had been rigorously excluded (entry 10), suggesting an alternative initiation pathway excluding oxygen could also operate.14 A reaction at 80 °C in the absence of light showed no conversion to 5. This data shows the nature of the solvent is not relevant for the initiation step and suggests a straightforward radical initiation process that results from visible-light excitation of an intermediate arising from an interaction between the alkyl halide and (Me3Si)3Si–H.Effect of different parameters on radical initiationa
EntrySolventDeviation in conditionsYield 5 (%)
1CH2Cl233
2THF68
3MeOH85
4EtOH55
5C6H1284
6PhH41
7PhMe34
8EtOH16 h86
9EtOH16 h, 455 nm filter82
10EtOH16 h, degassed47
11EtOH80 °C, dark0
Open in a separate windowaYields of 5 were calculated by 1H NMR using 1,1,2,2-tetrachloroethane as internal standard.With the operationally simple and mild reaction conditions for the homolysis of non-activated alkyl halides, we next focussed on benchmarking the process against existing transformations: namely the Giese addition reaction of alkyl-radicals to electron deficient alkenes. Therefore, using acrylamide 2a (as a representative alkene acceptor), 3.0 equivalents of iso-propyl iodide 1a (as a representative non-activated alkyl halide) and 1.5 equivalents of (Me3Si)3Si–H in MeOH at 0.1 M, we were pleased to find visible light irradiation of this reaction mixture led to the formation of alkylamide 3a in 59% assay yield (
EntrySolvent(Me3Si)3Si–HAlkyl-iodideConc.Yield 3aa (%)
1MeOH1.5 equiv.3.0 equiv.0.1 M59
2MeOH2.0 equiv.3.0 equiv.0.2 M66
3EtOH2.0 equiv.3.0 equiv.0.2 M79
4EtOH2.0 equiv.2.0 equiv.0.2 M77
5EtOH2.0 equiv.1.5 equiv.0.2 M70
6EtOH1.5 equiv.1.5 equiv.0.2 M47
Open in a separate windowaYields of 3a were calculated by 1H NMR using 1,1,2,2-tetrachloroethane as internal standard.We next turned attention to evaluating the scope of the reaction ( Open in a separate windowNext, the scope of the reaction in the alkyl halide component was investigated. Carbon-centred radicals formed through the visible-light/TTMS initiation pathway from simple tertiary alkyl-iodides (1-adamantyl to 3t and tert-butyl to 3u) underwent Giese addition with acrylamide 2a in excellent yields. A series of alkyl-iodides based on heterocyclic scaffolds were found to undergo smooth radical formation and Giese addition, providing products that can be further elaborated and could be utilized in the construction of pharmaceutically relevant molecules (3v–3ab). Finally, a selection of primary alkyl-iodides (3ac–ae) were found to be compatible with the radical activation mode and generated the linear alkyl products in good yields.We had recognized a report by the Merck discovery group who showed that a visible-light mediated Ir-catalyzed Giese addition using alkyl bromides also utilized (Me3Si)3Si–H as a reagent to propagate alkyl-radical formation (Fig. 2A).8b A distinct difference of our system is the departure from any requirement for a photocatalyst, which not only reduces the cost of the transformation but could offer an alternative protocol for Giese addition when redox sensitive groups appear in one of the coupling partners.Open in a separate windowFig. 2(A) Photocatalytic Giese addition with alkyl bromides mediated by (Me3Si)3Si–H; (B) catalyst-free visible-light/(Me3Si)3Si–H mediated Giese addition.Several simple mechanistic experiments were conducted to supplement those shown in Fig. 3A), confirming the intermediacy of an alkyl radical. This result suggests a pathway involving β-scission of the cyclopropylmethyl radical (to int-I) prior to addition to the alkene (to int-II), which is followed by 5-exo trig cyclization (to int-III) and HAT of the resulting methyl radical with (Me3Si)3Si–H to form cyclopentane 7. A reaction conducted using d5-EtOD showed no incorporation of deuterium in the product, thereby eliminating solvent participation in the radical interception step (Fig. 3B), as expected from the observations outlined in Open in a separate windowFig. 3(A) Evidence for alkyl-radical formation via radical trap experiment; (B) experiments to demonstrate HAT is not from solvent and the essential role of the silane.Despite the strength of our experimental observations, conclusive evidence that unravels the visible-light mediated radical initiation pathway between (Me3Si)3Si–H and the non-activated alkyl-iodide remains elusive. 1H NMR, UV-vis or IR spectroscopy titration studies aimed at identifying an interaction between a variety of alkyl-halides and (Me3Si)3Si–H could not be obtained (see ESI for details). However, visible light must be exciting a transient intermediate comprising the silane and alkyl-iodide as the predominant pathway here because the process so efficiently homolyzes the carbon–iodide bond15 to yield alkyl-radicals. Consequently, we hypothesized that such an interaction may not be observable due to its transient nature and short lifetime or would be present in minute quantities beyond the detection limits of these spectroscopic methods. One possibility for the radical initiation is the excitation of a halogen bonded intermediate between the alkyl iodide and silane – whereby a coulombic attraction between a region of electron deficiency around the polarizable halogen atom (σ-hole)16,17 and the electron rich hydridic component of the silane – could result in weakening of the carbon–iodine bond, subsequently absorbing low energy visible light to stimulate homolysis (Fig. 1D). We do, however, acknowledge that an as yet undetermined pathway could be responsible for the radical initiation pathway. Despite the uncertainty over the mode of radical initiation, our understanding of the mechanism responsible for this catalyst-free Giese addition is detailed in Fig. 4. Visible-light and silane-mediated carbon–iodide bond homolysis, generates an alkyl-radical to initiate the process. Addition of the alkyl-radical to the alkene acceptor generates a new electrophilic radical, which undergoes HAT with (Me3Si)3Si–H to form the product. The resulting (Me3Si)3Si radical now undergoes halogen atom transfer (XAT) with a new molecule of the alkyl-iodide, thereby propagating the radical chain.Open in a separate windowFig. 4Current proposed mechanism for metal-free Giese addition.In summary, we have developed an operationally straightforward method for alkyl-radical generation from non-activated alkyl-iodides and applied this protocol through the development of mild Giese addition. Through the action of visible light and (Me3Si)3Si–H, radical initiation from an alkyl-iodide is achieved under mild reaction conditions. No photocatalysts are required for this process. The range of alkyl-iodides and alkenes is very broad, and the reaction tolerates many sensitive functional groups. Considering current demand for saturated scaffolds in the drug discovery programs, we believe this strategy offers a potentially powerful method through which to combine two readily available classes of building blocks into complex molecules of biological and pharmaceutical interest. While the pathway of radical initation remains unclear, it is clear that the activation mode afforded by the combination of (Me3Si)3Si–H, alkyl iodide and visible-light provides a mild and general means for forming open shell alkyl intermediates.11,12 Subsequently, it is likely that this method will be useful to practitioners of synthetic chemistry in both academic and industrial settings.  相似文献   
45.
Isosorbide spacer containing gemini surfactants: surface and biochemical study     
Kushan Parikh  Bhavesh Mistry  Sarmita Jana  Tejal Gajaria  Sarita Gupta  Ranjitsinh V. Devkar  Sanjeev Kumar 《Colloid and polymer science》2015,293(5):1437-1446
  相似文献   
46.
Facile Synthesis,Characterization, and Fluorescence Studies of Novel Porphyrin Appended Thiazoles     
Bhupendra Mishra  K. P. Chandra Shekar  Anil Kumar  S. Phukan  S. Mitra  Dalip Kumar 《Journal of heterocyclic chemistry》2013,50(1):125-128
A facile and high yielding synthesis of porphyrin appended thiazoles 5 from the reaction of 5‐(4‐thiocarboxamidophenyl)‐10,15,20‐triphenylporphyrin with α‐bromo ketones has been described. The fluorescence studies of synthesized porphyrin appended thiazoles 5 in chloroform indicate that porphyrin π system is not greatly perturbed by substitution of a thiazole moiety at meso‐phenyl ring even in the excited state.  相似文献   
47.
A Facile One‐Pot Synthesis of 3,5‐Disubstituted Isoxazole Derivatives Using Hydroxy (Tosyloxy) Iodobenzene     
Ravindra D. Jadhav  Hitesh D. Mistry  Hashim Motiwala  Kishorkumar S. Kadam  Shivaji Kandre  Amol Gupte  Ashok K. Gangopadhyay  Rajiv Sharma 《Journal of heterocyclic chemistry》2013,50(4):774-780
Hydroxy (tosyloxy) iodobenzene (HTIB), a hypervalent iodine reagent, has been extensively used for oxidative transformations. We have developed a one‐pot synthesis wherein aldoximes when reacted with alkynes in the presence of HTIB result in the direct formation of isoxazoles. This simple and straightforward reaction allows for ease of purification while leading to the formation of high purity 3,5‐disubstituted isoxazoles in moderate yields.  相似文献   
48.
Rheological changes occurring during the storage of the system sodium dodecyl sulphate/1-hexadecanol/water     
D. B. Mistry  B. Warburton 《Rheologica Acta》1971,10(1):106-112
Summary The physical decomposition of the system formed when sodium dodecyl sulphate, 1-hexadecanol and water are heated, mixed and cooled could be achieved at an accelerated rate by cycling the storage temperature between 5–7 °C and 20–25 °C. This decomposition caused the formation of pearliness and the systems became progressively more fluid with loss in rigidity.The changes in the rheological properties of the systems were investigated at 25 °C using a modifiedWeissenberg Rheogoniometer, anEpprecht Rheomat 15 viscometer, and a concentric cylinder air turbine viscometer.The systems are referred to by a code Rx where x is the molar ratio of 1-hexadecanol to sodium dodecyl sulphate. The systems R1–R10 were examined during temperature cycling for a maximum period of eight days. During this period, the systems R1–R4 progressively increased in consistency when examined in continuous shear using anEpprecht Rheomat 15, concentric cylinder viscometer. System R5 was also examined using anEpprecht Rheomat 15, but after increasing in consistency up to the fourth day, thereafter decreased in consistency. Systems R3 to R10 were investigated in creep mode. For R3 and R4, the compliance progressively decreased over a period of eight days, whereas for systems R5–R8 compliance was found to pass through a minimum about four days after preparation and the start of temperature cycling. Thereafter it increased. For R9 and R10, the creep compliance at one hour increased continuously during the eight day period.
Zusammenfassung Beschleunigte Zersetzung des Systems, das beim Erwärmen, Mischen und Kühlen von Natriumdodecylsulfat, 1-Hexadekanol und Wasser entsteht, wurde durch zyklische Temperaturänderungen zwischen 5–7 und 20–25 °C bewirkt. Durch Zersetzung wurde das System perlmutterartig verfärbt und unter Verlust an Festigkeit fließfähiger.Die Änderungen im rheologischen Verhalten wurden mit einem modifiziertenWeissenberg-Rheogoniometer, einem Rheomat-15-Viskosimeter, und einem Luftturbinen-Viskosimeter mit konzentrischen Zylindern untersucht.Auf die verschiedenen Systeme wird mit einem Code Rx Bezug genommen, wobei x das molare Verhältnis von 1-Hexadekanol zu Natriumdodecylsulfat ist. Die Systeme R1–R10 wurden über einen Zeitraum von 8 Tagen unter dem Einfluß von zyklischen Temperaturänderungen untersucht. Innerhalb dieses Zeitraumes nahmen die flüssigen Systeme R1–R4, wie kontinuierliche Scherexperimente mit dem Rheomat 15 Viskosimeter (konzentrische Zylinder) zeigten, beständig an Konsistenz zu. System R5 wurde auch mit dem Rheomat 15 untersucht; es zeigte aber, nach einer Konsistenzzunahme bis zum 4. Tag, eine Abnahme an Konsistenz. Die Systeme R6–R10, die mehr Festkörper-Charakter hatten, wurden mit Hilfe von Kriechtesten untersucht. Die dynamische Nachgiebigkeit bei 1 Std. ging durch ein Minimum 4 Tage nach der Herstellung bei Lagerung mit zyklischer Temperaturänderung. Danach nimmt sie zu. Für R9–R10 nahm die dynamische Nachgiebigkeit bei 1 Std. kontinuierlich über die 8 Tage zu.


Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14–15, 1970.  相似文献   
49.
On-line, real time monitoring of exhaled trace gases by SIFT-MS in the perioperative setting: a feasibility study     
Boshier PR  Cushnir JR  Mistry V  Knaggs A  Španěl P  Smith D  Hanna GB 《The Analyst》2011,136(16):3233-3237
A study is described of the first on line, real time analyses of the exhaled breath of five anaesthetized patients during the complete perioperative periods of laparoscopic surgery. These breath analyses were achieved using a selected ion flow tube, SIFT-MS, instrument, located in the operating theatre at an acceptable distance from the operating table, and coupled to the endotracheal tube in the ventilation circuit via a 5 metre long capillary tube. Thus, inhalation/exhalation breathing cycles, set to be at a frequency of 10 per minute, were sampled continuously for water vapour, the metabolites acetone and isoprene and the propofol used to induce anaesthesia for each operating period that ranged from 20 min (shortest) to 80 min (longest). Whilst there was some loss of water vapour along the long sampling line, the concentrations of the other trace compounds were not diminished. The breath acetone was essentially at a constant level for each patient, but increased somewhat over the longest operating period due to the onset of lipolysis. Most interesting is the clear increase of breath isoprene following abdomen inflation with carbon dioxide. The vapour of the intravenously injected propofol was detected in the exhaled breath and remained essentially constant during the perioperative period. These analyses were performed totally non-invasively and the data were immediately and constantly available to the anaesthetist and surgeon. Exploitation of this development could influence decision making and potentially improve patient safety within the perioperative setting.  相似文献   
50.
Succinct and Facile Synthesis of Innovative Thiopyrimidines With Antimicrobial and Antitubercular Investigation     
Prashant T. Mistry  Nimesh R. Kamdar  Dhaval D. Haveliwala  Saurabh K. Patel 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):561-572
Abstract

To develop a series of bioactive heterocycles in minimum number of steps, 3-methyl- 4-(substituted phenyl)-1-phenyl-4,8-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5,7 (1H,6H)-dithione 2(a–j), 4-(4-substituted phenyl)-5-imino-3-methyl-1,6-diphenyl-4,5,6,8-tetrahydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-7(1H)-thione 3(a–j), and N-[4-(subs- tituted phenyl)-3-methyl-1-phenyl-7-thioxo-1,4,7,8-hexahydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5-yl]thiourea 4(a–j) have been synthesized from amino nitrile functionality 1(a–j). The structures of the compounds were elucidated by IR, 1H NMR, elemental analysis, and some representative 13C NMR and mass spectra. All the title compounds were screened for antimicrobial and antitubercular activities, while some representative compounds were tested for antioxidant activity. Out of synthesized compounds, compounds 1j (4-CH3), 2d (4-F), 4c (4-OH), and 4i (3-Br) exhibited maximum inhibition against Mycobacterium Tuberculosis H37Rv. Compound 3c (4-OH) revealed elevated efficacy against all tested bacterial strain, while compounds 1i (3-Br), 2c (4-OH), and 3h (3-NO2) were found efficacious against Candida albicans as compared to standard drugs.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.  相似文献   
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