Metal-free C–H mercaptalization of benzothiazoles and benzoxazoles using 1,3-propanedithiol as thiol source

• Yan Xiao,
• Bing Jing,
• Xiaoxia Liu,
• Hongyu Xue and
• Yajun Liu

Beilstein J. Org. Chem. 2019, 15, 279–284, doi:10.3762/bjoc.15.24

• [22] and 1,2-ethanedithiol [23]. In the past decades, C–H functionalization has become an effective strategy for constructing different molecules directly from simple arenes and alkanes. C–H functionalization is an important method for C–S coupling reactions [24][25]. For example, transition metal

Synthesis of a tyrosinase inhibitor by consecutive ethenolysis and cross-metathesis of crude cashew nutshell liquid

• Jacqueline Pollini,
• Valentina Bragoni and
• Lukas J. Gooßen

Beilstein J. Org. Chem. 2018, 14, 2737–2744, doi:10.3762/bjoc.14.252

• based on cross-metathesis of CNSL with ethylene [33][34][35]. Each unsaturated double bond isomer has the first double bond located at the C-8 position, so that no matter how many other double-bonds are present, the unsaturated side chains of all arenes will be shortened to ω-nonenyl groups if ethylene

Gold-catalyzed post-Ugi alkyne hydroarylation for the synthesis of 2-quinolones

• Xiaochen Du,
• Jianjun Huang,
• Anton A. Nechaev,
• Ruwei Yao,
• Jing Gong,
• Erik V. Van der Eycken,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2018, 14, 2572–2579, doi:10.3762/bjoc.14.234

• –Crafts-type cyclizations involving attack of electron-rich arenes on the triple bonds, leading to the formation of a great number of fused [50][51][52][53] and spirocyclic structures [54][55][56][57][58][59]. In addition, Ugi adducts have already been successfully utilized for the diversity-oriented

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• Amrita Das Mitasree Maity Simon Malcherek Burkhard Konig Julia Rehbein Department of Chemistry and Pharmacy, Institute of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany 10.3762/bjoc.14.228 Abstract Electron-rich arenes react with aryl and alkyl

• disulfides in the presence of catalytic amounts of [Ir(dF(CF3)ppy)2(dtbpy)]PF6 and (NH4)2S2O8 under blue light irradiation to yield arylthiols. The reaction proceeds at room temperature and avoids the use of prefunctionalized arenes. Experimental evidence suggests a radical–radical cross coupling mechanism

• . Keywords: arenes; oxidation; photocatalysis; thiolation; visible light; Introduction The generation of carbon–sulfur bonds is an important task in organic synthesis, because of their abundance in target structures, such as natural products and drugs [1][2][3]. They are found in organic semiconductors

Calixazulenes: azulene-based calixarene analogues – an overview and recent supramolecular complexation studies

• Paris E. Georghiou,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Hidetaka Nishimura,
• Jaehyun Lee,
• Atsushi Wakamiya and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2018, 14, 2488–2494, doi:10.3762/bjoc.14.225

• relatively facile and reproducible syntheses of the classical calix[n]arenes 1 in which n = 4, 6 or 8, with phenolic groups linked or bridged via methylene groups to form defined three-dimensional basket-like cavities with “upper” or “lower” rims, were developed by Gutsche and co-workers [4][5][6]. As a

• result of Gutsche’s synthetic methodologies many researchers have been able to employ these calix[n]arenes and modified derivatives thereof in a great variety of ingenious applications. These applications have included a myriad of synthetic modifications to both, or either, of their upper and lower rims

• . Since these three calix[4]azulenes 3–5 are all-hydrocarbon compounds they differ significantly from the better-studied calix[4]arenes, which usually have some heteroatoms such as oxygen, nitrogen or sulfur in their structures. As a consequence, compounds 3–5 have solubility limitations. Furthermore, the

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• AlMe2(OMe), and methyl–Rh(I) A is regenerated. Later, Iwasawa et al. achieved the Rh-catalyzed direct carboxylation of arenes without any directing group (Scheme 30) [60][61]. The reactions proceeded using a catalytic amount of Rh complex bearing dcype (dcype = 1,2-bis(dicyclohexylphosphino)ethane) as

• the ligand and AlMe2(OEt) as a reducing agent in a mixture of DMA and 1,1,3,3-tetramethylurea (TMU) as a solvent. Under the reaction conditions, benzene (32a) was converted into benzoic acid (33a, TON: 37) at 85 °C. The monosubstituted arenes such as toluene (32b), fluorobenzene (32c), and

Practical tetrafluoroethylene fragment installation through a coupling reaction of (1,1,2,2-tetrafluorobut-3-en-1-yl)zinc bromide with various electrophiles

• Ken Tamamoto,
• Shigeyuki Yamada and
• Tsutomu Konno

Beilstein J. Org. Chem. 2018, 14, 2375–2383, doi:10.3762/bjoc.14.213

• ), demonstrating a promising pathway for constructing CF2CF2-containing heterocyclic compounds. We also demonstrated the multigram preparation of CF2CF2-containing arenes through the present cross-coupling reaction, as shown in Scheme 2. Thus, treatment of 1.38 g (5.00 mmol) of ethyl o-iodobenzoate (3j) with 10.1

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• functionalization. Of these reactions, alkylation, alkenation, amidation, and cyclization of arenes with the relevant coupling partners are an economical and straightforward approach for the synthesis of diverse alkyls, alkenes, amides and cyclic compounds. A simple addition of a “inert” C–H bond to multiple bonds

• . The hydroarylation reaction further extended to pyrroles for selective monoalkenylation using [Cp*Co(CH3CN)3](SbF6)2 as the catalyst [55]. In contrast, branched-selective hydroarylation of terminal alkynes was achieved by Li et al. The addition of arenes 7 to propargyl alcohols, protected propargyl

• developed a hydroarylation of alkynes with different arenes including phenylpyridines, pyrazole, and 6-arylpurines 17 using 5 mol % Cp*Co(CO)I2, 10 mol % AgSbF6, and 0.5 equiv PivOH in DCE (Scheme 13) [57]. The reaction proceeded efficiently with various alkynes to give alkenes 18, however, the reaction was

Synthesis of a water-soluble 2,2′-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine

• Xiayang Huang,
• Xinghua Zhang,
• Tianxin Qian,
• Junwei Ma,
• Lei Cui and
• Chunju Li

Beilstein J. Org. Chem. 2018, 14, 2236–2241, doi:10.3762/bjoc.14.198

• , medicine, and environment. Cyclodextrins [1][2][3][4], cucurbiturils [5][6][7][8][9][10][11], and calixarenes [12][13][14][15][16][17][18][19][20] have been widely used in aqueous supramolecular chemistry. In the past ten years, the chemistry of pillar[n]arenes has developed very quickly because of their

• the blood stream, but also be effectively dis-assembled in the acidic tumor environment, and thus improve the anticancer activity of oxaliplatin in vivo. In 2015, we introduced a new class of macrocyclic arenes, 4,4’-biphen[n]arenes (n = 3,4) with 4,4’-biphenol or 4,4’-biphenol ether monomers linked

• by –CH2– bridges [41], which have received much attention due to their convenient synthesis and modification method, novel topological structures and excellent cavity host–guest properties [41][42][43][44][45][46]. In 2017, another type of biphen[n]arenes with 2,2’-disubstituted biphenyl units, 2,2

Synthesis and post-functionalization of alternate-linked-meta-para-[2ⁿ.1ⁿ]thiacyclophanes

• Wout De Leger,
• Koen Adriaensen,
• Koen Robeyns,
• Luc Van Meervelt,
• Joice Thomas,
• Björn Meijers,
• Mario Smet and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2190–2197, doi:10.3762/bjoc.14.192

• cyclophanes is formed by thiacyclophanes, in which the thioether linkages impose less conformational strain and which have an increased cavity size compared to other (oxa/aza)cyclophanes. Thiacalix[n]arenes are among the most widely known thiacyclophanes with significant ability for molecular recognition [5

• ][6][7][8][9]. Our group has experience in the synthesis of homothiacalix[n]arenes, a subclass of the thiacalix[n]arenes that has so far received little attention compared to other homoheteracalix[n]arenes [10][11]. Homothiacalix[4]arenes were successfully synthesized via nucleophilic substitution and

• homodithiacalix[4]arenes by dynamic covalent chemistry [12][13][14]. Functionalization of homothiacalix[4]arenes was made possible by changing the precursors before macrocyclization (Scheme 1) [12]. Recently, pillar[n]arenes have attracted much interest as new supramolecular receptors due to their pillar-shaped

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• catalysis [24]. The widespread use of the calixarene derivatives is due to their convenient synthesis and to their chemical and conformational versatility [25]. In fact, calixarene macrocycles present a conformational isomerism that in the case of calix[6]arenes gives rise to eight discrete conformations

• conformation of calix[6]arenes when the alkyl substituents at the lower rim are increased in size [41]. As expected [40], no evidence of interaction between 2+ and 1 was detected by NMR, when 2+ was added as its chloride salt to a CDCl3 solution of 1. However, when 2+ was added as its TFPB− salt to a CDCl3

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

• Jiao-Na Han,
• Cong Du,
• Xinju Zhu,
• Zheng-Long Wang,
• Yue Zhu,
• Zhao-Yang Chu,
• Jun-Long Niu and
• Mao-Ping Song

Beilstein J. Org. Chem. 2018, 14, 2090–2097, doi:10.3762/bjoc.14.183

• alcohols was first reported by the Niu and Song group (Figure 1a) [30]. Successively, Ackermann realized the electrochemical cobalt-catalyzed alkoxylation via a similar process (Figure 1b) [32]. However, cobalt-catalyzed directed coupling of arenes with secondary alcohols has not been reported so far

• alkoxylation of arenes with primary alcohols [30][31], HFIP (2a), isopropanol (2t), isobutanol (2u), and isopentanol (2v) could all proceed smoothly to deliver the alkoxylated products in 58–89% yields. Furthermore, we attempted some tertiary alcohols (tert-butanol and 2-methyl-2-butanol). However, no desired

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• , as well as aliphatic chains. Unsurprisingly, esters and other base labile groups are not encountered. A recent publication by König and his group shows the DDQ catalysed (3DDQ Ered*(cat/cat•−) ≈ +3.18 V vs SCE) C–H amination of arenes and heteroarenes using weakly nucleophilic species such as

• carbamates, urea and non-basic heterocycles (Scheme 11) [54]. The scope covers a multitude of electron-poor and electron-rich arenes which can be reacted with carbamates, urea, pyrazole and triazole derivatives to furnish aminated products. The authors address the various reactivities observed with respect

• to both the electronics of the arene and the nucleophilicity of the amine. Particularly electron-rich arenes such as N-methylindole are not tolerated, as is the case for relatively nucleophilic amines such as imidazoles, anilines or alkylamines. The reported substrates are particularly valuable to

Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates

• Vladimir A. Burilov,
• Guzaliya A. Fatikhova,
• Mariya N. Dokuchaeva,
• Ramil I. Nugmanov,
• Diana A. Mironova,
• Pavel V. Dorovatovskii,
• Victor N. Khrustalev,
• Svetlana E. Solovieva and
• Igor S. Antipin

Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173

• /bjoc.14.173 Abstract The synthesis of new calix[4]arenes adopting a cone stereoisomeric form bearing two or four azide fragments on the upper rim and water-soluble triazolyl amphiphilic receptors with two or four polyammonium headgroups via copper-catalyzed azide–alkyne cycloaddition reaction has been

• binding sites offering multipoint interactions with a substrate for the effective complexation [13]. Calix[4]arenes and their thia analogues have many advantages over other macrocycles that are frequently used as synthetic receptors, such as cyclodextrins [14], cucurbiturils [15], and pillararenes [16

• solutions. Results and Discussion Synthesis of polyammonium calix[4]arene derivatives The functionalization of calix[4]arenes with azide groups paves the way to introduce a wide variety of functional groups [27] on the upper rim of the macrocycle by, e.g., the copper-catalyzed azide–alkyne cycloaddition

An amphiphilic pseudo[1]catenane: neutral guest-induced clouding point change

• Tomoki Ogoshi,
• Tomohiro Akutsu and
• Tada-aki Yamagishi

Beilstein J. Org. Chem. 2018, 14, 1937–1943, doi:10.3762/bjoc.14.167

• aggregation of the hydrophobic alkyl chain rings, which induced insolubilization of the bicyclic compound in aqueous media at 20 °C and a decrease in its clouding point. Keywords: amphiphilic molecules; host–guest complexes; lower critical solution temperature; pillar[n]arenes; pseudo[1]catenane

• –guest chemistry [5][6][7]. The molecules consist of a non-ionic amphiphilic part containing tri(ethylene oxide) moieties, and a hydrophobic part consisting of a pillar[n]arene core (Figure 1a; 1, n = 5; 2, n = 6). Pillar[n]arenes, which were first reported by our group [11], were used as the macrocyclic

• component because of their high functionality and superior host–guest properties with neutral guests [12][13][14][15][16]. The amphiphilic pillar[n]arenes 1 and 2 exhibit clouding points at 41 and 42 °C, respectively [5][6]. The oligo(ethylene oxide) moieties are solvated with water molecules at room

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• protocol acted as an asymmetric gateway to the useful vicinal diamines. Aminofluorination of alkenes (Difluoroiodo)arenes (Ar-IF2), which can be prepared from HF with iodosoarenes, are hypervalent iodine compounds suitable for the fluorination of alkenes [59]. Based on Nevado’s stoichiometric

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• theoretical isotope patterns confirms (inset Figure 6) that irradiation of conjugate 9 and GMP efficiently yielded the desired photoadduct. Conclusion The present work validates the design strategy that consists in using calix[4]arenes as addressable platforms for the elaboration of multivalent photoreactive

• Information File 1. Calix[4]arenes 2 and 3 were synthesized from commercial p-tert-butylcalix[4]arene 1 according to procedures described in the literature [69]. The experimental procedures and characterization data for calixarene derivatives 4, 6, 7 and 9, phenanthroline derivative 5 and c-[RGDfK]-alkyne 8

Synthesis of diamido-bridged bis-pillar[5]arenes and tris-pillar[5]arenes for construction of unique [1]rotaxanes and bis-[1]rotaxanes

• Ying Han,
• Li-Ming Xu,
• Cui-Yun Nie,
• Shuo Jiang,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2018, 14, 1660–1667, doi:10.3762/bjoc.14.142

• sequential alkylation of ω-bromoalkoxy-substituted pillar[5]arenes with methyl or ethyl p-hydroxybenzoate followed by a hydrolytic reaction under basic conditions. Under catalysis of HOBt/EDCl, the amidation reaction of pillar[5]arene mono(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes

• afforded diamido-bridged bis-pillar[5]arenes. 1H NMR and 2D NOESY spectra clearly indicated that [1]rotaxanes were formed by insertion of longer diaminoalkylene unit into the cavity of one pillar[5]arene with another pillar[5]arene acting as a stopper. The similar catalysed amidation reaction of pillar[5

• ]arene di(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes resulted in the diamido-bridged tris-pillar[5]arenes, which successfully form the unique bis-[1]rotaxanes bearing longer than diaminopropylene diamido bridges. Keywords: bis-[1]rotaxane; mechanically interlocked molecule

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• implemented in the preparation of novobiocin analogues [65], and formed a key step in the synthesis of new glycosidic PDE4 (phosphodiesterase type 4) inhibitors [66]. Also calix[4]arenes could be selectively mono- or diglycosylated by means of the Mitsunobu methodology [67][68]. The Mitsunobu reaction was

Direct electrochemical generation of organic carbonates by dehydrogenative coupling

• Tile Gieshoff,
• Vinh Trieu,
• Jan Heijl and
• Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2018, 14, 1578–1582, doi:10.3762/bjoc.14.135

• organic acetonitrile-based electrolyte system. Acetonitrile tolerates highly positive potential regimes, which are necessary for C–H activation of non-functionalized arenes. Since simple metal-based carbonate salts are not sufficiently soluble in organic media, the choice of carbonate source is crucial

• nucleophilicity of carbonates is limited and therefore, the choice of suitable arenes is crucial. Heterofunctionalizations like fluoro, chloro, and methoxy groups are generally accepted, but it depends on the substitution pattern. The sensitive interplay of inefficient oxidation at highly positive oxidation

• potentials and the oligomerization tendency of electron-rich arenes limit the scope (see Supporting Information File 1). Conclusion The first direct electrochemical generation of organic carbonates by dehydrogenative coupling at arenes was established. Even though this ambitious method is currently

A conformationally adaptive macrocycle: conformational complexity and host–guest chemistry of zorb[4]arene

• Liu-Pan Yang,
• Song-Bo Lu,
• Arto Valkonen,
• Fangfang Pan,
• Kari Rissanen and
• Wei Jiang

Beilstein J. Org. Chem. 2018, 14, 1570–1577, doi:10.3762/bjoc.14.134

• biomimetic structures [24]: endo-functionalized molecular tubes [25][26][27][28][29][30] and conformationally adaptive macrocycles [31][32][33][34][35][36][37]. Among the conformationally adaptive macrocycles two types were reported: oxatub[n]arenes [31][32][33][34][35][36] and zorb[n]arenes [37]. These

• network. We have carefully looked into the properties of oxatub[n]arenes and found that the macrocycles have many unique properties. For example, oxatub[4]arene has a wide guest scope and can bind almost all of the common organic cations [32]. It also shows conformational responses to solvent change [33

• ] and remote electronic substituents on the guests [34]. In addition, different alkyl side chains on oxatub[4]arenes lead to different macroscopic self-assembly behaviors [36]. Zorb[4]arene was first synthesized, reported and so named by the Georghiou group in 2005. The derivatives per-O-methoxy- and

Cobalt-catalyzed C–H cyanations: Insights into the reaction mechanism and the role of London dispersion

• Eric Detmar,
• Valentin Müller,
• Daniel Zell,
• Lutz Ackermann and
• Martin Breugst

Beilstein J. Org. Chem. 2018, 14, 1537–1545, doi:10.3762/bjoc.14.130

• cyanation of arenes (Scheme 2) [30][31][32][33][34]. Dispersion effects can be envisioned to be highly important in this system, as the relatively C–H-rich ligand Cp* can interact with both substrates within the cobalt complexes. In 2015, Li and Ackermann have proposed the catalytic cycle (C–H cobaltation

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• , arenes and heteroarenes [43][44]. A first solution to value the 2-iodobenzoic moiety released from EBX has arisen from the reaction of derivatives 22 with N-(aryl)imines 23 in the presence of 10 mol % of Pd(OAc)2, which gives access to tri- or tetrasubstituted furans 24 and N-(aryl)formamides 25 (Scheme

• this issue of atom-economy, the group of Shafir has reported the metal- and base-free arylation of keto-esters and cyanoketones using [bis(trifluoroacetoxy)iodo]arenes ArI(OCOCF3)2 (Scheme 40) [78]. The reaction can also be applied to cyclic 1,3-diones with equal efficiency [79]. Mechanistic studies

• using Oxone as a terminal oxidant, thereby allowing for extending the scope of the reaction in terms of iodoarenes. Tandem oxidation–catalytic couplings A large range of oxidation reactions can be performed with [bis(acyloxy)iodo]arenes best represented by the commercially available reagents PhI(OAc)2

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst

• Kimihiro Komeyama,
• Shunsuke Sakiyama,
• Kento Iwashita,
• Itaru Osaka and
• Ken Takaki

Beilstein J. Org. Chem. 2018, 14, 1413–1420, doi:10.3762/bjoc.14.118

• characters of organometallics depending on the central metals. Ni/Cr or Co/Cr-catalyzed NHK reaction. Functionalization of alkynes via carbocobaltation. Cyclization/borylation of alkynyl iodoarenes using the Co/Cr catalyst. Three-component coupling of aryl iodides, arenes, and aldehydes using Co/Cr catalyst

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• chiral calix[4]arenes (±)-1 and (±)-2 containing a quaternary ammonium moiety together with a hydroxymethyl and diarylmethanol moiety in an optically pure form, respectively (Figure 1) [37]. In order to see the beneficial effect of the diarylmethanol structure in this catalysts, they were applied to the

• asymmetric phase-transfer catalysis based on inherently chiral calix[4]arenes, although the asymmetric induction observed remained moderate. Su et al. demonstrated a new approach for the design of a chiral binary integrative phase-transfer catalyst consisting of p-tert-butylcalix[4]arene and a cinchonine

• investigated. Under optimized conditions, up to 47% ee was obtained by alkylation of 3 with 4-methylbenzyl bromide in the presence of 5 mol % catalyst 12. Henry reaction Since lower-rim functionalization of calix[4]arene is relatively easy, a variety of inherently chiral calix[4]arenes substituted at the lower