The direct oxidative diene cyclization and related reactions in natural product synthesis

• Juliane Adrian,
• Leona J. Gross and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2016, 12, 2104–2123, doi:10.3762/bjoc.12.200

• an oxidative cyclization using stoichiometric amounts of sodium permanganate to furnish trans-THF diol 78 in 73% yield with an excellent diastereomeric ratio of 97:3 induced by a cyclohexanol derived chiral auxiliary. This key intermediate was subsequently converted to natural trans-(+)-linalool

• be solved in future investigations. To date there is only a single report on an enantioselective oxidative cyclization of a 1,5-diene using permanganate together with a chiral counter ion. Other strategies use either a chiral auxiliary, a subsequent desymmetrization or start from a chiral 5,6

Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes

• Lucie Brulíková,
• Aidan Harrison,
• Marvin J. Miller and
• Jan Hlaváč

Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184

• nitroso dienophiles with masked o-benzoquinones [128]. For instance, they synthesized synthon 152 from 2-methoxyphenol (150) and the chiral auxiliary 151 with 99% de, which was further utilized for the synthesis of (+)-conduramine E-1 (153, Scheme 30). The hetero-Diels–Alder reaction of chloronitroso

• enantioselectivity encouraged the Inomata group to further investigate the reaction [152]. Their investigation of enantioselective hetero-Diels–Alder reactions resulted in an enantioselectivity of up to 92% ee, when nitrosobenzene and a dienol were reacted in the presence of tartaric acid ester as a chiral auxiliary

Experimental and theoretical insights in the alkene–arene intramolecular π-stacking interaction

• Valeria Corne,
• Ariel M. Sarotti,
• Carmen Ramirez de Arellano,
• Rolando A. Spanevello and
• Alejandra G. Suárez

Beilstein J. Org. Chem. 2016, 12, 1616–1623, doi:10.3762/bjoc.12.158

• reported the synthesis of a novel chiral auxiliary that demonstrated to be very efficient in an asymmetric Diels–Alder reaction between the acrylic ester derivative and cyclopentadiene [16]. The facial selectivity of this reaction proved to be due to an aryl–vinyl π-stacking intramolecular interaction that

• fixed the conformation of the dienophile (Figure 1) [16]. Given this precedent, we aimed to gain further insight into this type of interaction, by exploring the effect caused by the introduction of electronically different substituents at the aromatic ring of the chiral auxiliary. For this reason, we

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• length via stereospecific nucleophilic displacement of the chiral auxiliary with complete inversion of configuration at the sulfur center [46][47]. Sulfoxide 3 is incorporated into the catalyst via a [3 + 2] oxidative cycloaddition with allylruthenium complex 4. Desilylation of cationic complex 5, ion

Opportunities and challenges for direct C–H functionalization of piperazines

• Zhishi Ye,
• Kristen E. Gettys and
• Mingji Dai

Beilstein J. Org. Chem. 2016, 12, 702–715, doi:10.3762/bjoc.12.70

• α-methylbenzyl group is bulky enough to prevent the aforementioned side reactions and the resulting diastereomeric α-functionalized piperazines could then afford good separation. Furthermore, this “chiral auxiliary” can be removed upon catalytic hydrogenation. As shown in Figure 10, a variety of

• ), product 39 was produced in only 49% yield with poor diastereoselectivity (67:33). This result indicates a mismatched case of (−)-sparteine and the (S)-α-methylbenzyl group even though the chiral center of the “chiral auxiliary” is quite far away from the newly established chiral center. This issue is

• . As shown in Figure 11, they have tried various reaction conditions to achieve an enantioselective methylation of the α-lithiation intermediate of N-Boc-N’-alkylpiperazines by using different diamines (TMEDA, 21, and 28) as well as the “chiral auxiliary” strategy. While the result is not yet optimal

A novel and practical asymmetric synthesis of dapoxetine hydrochloride

• Yijun Zhu,
• Zhenren Liu,
• Hongyan Li,
• Deyong Ye and
• Weicheng Zhou

Beilstein J. Org. Chem. 2015, 11, 2641–2645, doi:10.3762/bjoc.11.283

• ., Shanghai 201203, China 10.3762/bjoc.11.283 Abstract A novel and practical asymmetric synthesis of dapoxetine hydrochloride by using the chiral auxiliary (S)-tert-butanesulfinamide was explored. The synthesis was concise, mild, and easy to perform. The overall yield and stereoselectivity were excellent

• encompass asymmetric dihydroxylation of trans-methyl cinnamate or cinnamyl alcohol [6], chiral azetidin-2,3-dione [7], asymmetric C–H amination reactions of a prochiral sulfamate [8], oxazaborolidine reduction of 3-chloropropiophenone or ketone [9], and an imidazolidin-2-one chiral auxiliary mediated

• N-tert-butanesulfinylimine intermediates [11][12]. Due to its high diastereoselectivity and convenient cleavage of the N-tert-butanesulfinyl group, it has become an excellent chiral auxiliary in the synthesis of chiral amine compounds [13]. This work was devoted to develop an efficient synthetic

Recent advances in copper-catalyzed asymmetric coupling reactions

• Fengtao Zhou and
• Qian Cai

Beilstein J. Org. Chem. 2015, 11, 2600–2615, doi:10.3762/bjoc.11.280

• for the formation of carbon–carbon and carbon–heteroatom bonds as well as the asymmetric allylic substitution with a wide range of nucleophiles for the formation of C–C and carbon–heteroatom bonds. Review Copper-catalyzed coupling of aryl halides with nucleophiles Chiral auxiliary-induced aryl C–C

• of trans-4,5,9,10-tetrahydroxy-9,10-dihydrophenanthrene at room temperature (Scheme 4). In 1994, Meyers and Nelson [23][24] developed a copper-mediated asymmetric biaryl coupling with oxazoline as the chiral auxiliary to afford the biaryl-coupling products in high diastereomeric purity (dr = 93:7

• intramolecular oxidative biaryl-coupling through the formation of higher-order cyanocuprates. The authors realized an asymmetrical intramolecular reaction by means of inexpensive optically active auxiliary bridges. The most efficient chiral auxiliary was found to be a C2-symmetrical bridge bearing two

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• construction of the cyclononene unit [49]. The synthesis started with a diastereoselective Evans syn-aldol reaction between substituted propanal 86 and E-crotonyl-oxazolidinone 85 (Scheme 9). The resulting secondary alcohol was silylated and the chiral auxiliary was cleaved with lithium borohydride. Acylation

• butenolide 140 from (R)-citronellol (139) in an 11-step sequence. Next, the two stereocenters at C2 and C3 position were installed by stereoselective conjugate addition of enantiopure α-allylphosphonamide 141 to butenolide 140. After cleavage of the chiral auxiliary by ozonolysis, aldehyde 142 was protected

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• . The menthyloxy chiral auxiliary directed the addition of the amine moieties exclusively from the less hindered face but, due to poor selectivity at the chiral centers forming alpha to the nitrogen, the diastereomeric excesses of 7a,b were poor (Scheme 3). The method was generalized for the addition of

The enantioselective synthesis of (S)-(+)-mianserin and (S)-(+)-epinastine

• Piotr Roszkowski,
• Jan. K. Maurin and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2015, 11, 1509–1513, doi:10.3762/bjoc.11.164

• mianserin was originally described by Organon [4][5], and in 1999 Jackson and Subasinghe presented a method for the separation of mianserin enantiomers with (+)- or (−)-di-p-toluoyltartaric acid [6]. Later, the diastereoselective synthesis of (R)-mianserin using (S)-(−)-α-methylbenzylamine as a chiral

• auxiliary was described by the Czarnocki group [7]. For the commercial manufacture of mianserin enantiomers both the above mentioned processes are rather unjustified economically and the most advantageous method could be the enantioselective synthesis. Considering our experience in asymmetric synthesis of

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• chirality of the Michael acceptors can be attributed to one of two factors: 1) use of a chiral auxiliary attached to the nitrogen or 2) existing stereochemistry of the acceptor. In this section, we will briefly discuss the use of both types of chiral Michael acceptors in DCA of α,β-unsaturated amides and

• lactams. 1.1 DCA using chiral auxiliaries Chiral auxiliaries have been useful tools to induce stereoselectivity in C–C bond forming reactions [5][32][33][34]. Ideally, these compounds are stable, easily attached, removed and recoverable. One of the first examples of a DCA reaction using a chiral auxiliary

• was done by Mukaiyama and Iwasawa in 1981 [28]. DCA reactions were performed on a series of α,β-unsaturated amides, which employed L-ephedrine as a chiral auxiliary (Scheme 2). Mechanistically, it was supposed that the Grignard reagent formed an internal chelate between the nitrogen and the oxygen on

The Shono-type electroorganic oxidation of unfunctionalised amides. Carbon–carbon bond formation via electrogenerated N-acyliminium ions

• Alan M. Jones and
• Craig E. Banks

Beilstein J. Org. Chem. 2014, 10, 3056–3072, doi:10.3762/bjoc.10.323

• stainless steel cathode were utilised in a flow cell set-up [35]. An important example of the scope and synthetic potential of the silyl electroauxiliary approach was reported by Yoshida (Scheme 5) in combination with a chiral auxiliary a highly diastereoselective cationic carbohydroxylation occurred [18

• –silicon bond (when an electroauxiliary is present) or direct carbon–hydrogen bond fission to afford the α-methoxylated product (Scheme 10) [67][68]. The direct anodic oxidation reaction to afford the N-acyliminium ion can be intercepted with a carbon nucleophile enantioselectively when a chiral auxiliary

• were intercepted with cyanide [71]. The enantioselectivity induced in this step was as a result of using a chiral auxiliary, 8-phenylmenthyl attached to the carbamate (Scheme 19). Other natural product syntheses have used the anodic oxidation approach, often as the first step in a synthesis campaign to

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• substituents with a minimum of experimental work being invested as long as reliable CDA is employed. In all of our previous studies α-methoxy-α-phenylacetic acid (O-methylmandelic acid, MPA) used in both enantiomeric forms turned out to be an excellent chiral auxiliary reagent for this type of derivatized

• phenyl ring of the chiral auxiliary regent MPA), showed appropriate strength (intensity) giving rise to perceptible shifts in the 1H NMR signals of the L1/L2 groups located close to the chiral carbon in each of the investigated derivatives 11 and 12. (iii) The 1H NMR signals of the chiral MPA shift

(2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-Mono(di,tri)fluoromethylcyclopropyl]alanines and their incorporation into hormaomycin analogues

• Armin de Meijere,
• Sergei I. Kozhushkov,
• Dmitrii S. Yufit,
• Christian Grosse,
• Marcel Kaiser and
• Vitaly A. Raev

Beilstein J. Org. Chem. 2014, 10, 2844–2857, doi:10.3762/bjoc.10.302

• corresponding (2S,1'S,2'R)- [see Scheme 3, derived from (S)-10] and (2R,1'S,2'R)-3-(2'-fluoromethylcyclopropyl)alanines [derived from (R)-10] in good to excellent yields. The chiral auxiliary was recovered as the hydrochloride of 2-[(N-benzylprolyl)amino]benzophenone (~95%). (R)-allo-Threonine (4) is

• with alkyl halides virtually yield single stereoisomers, in which the configuration of the newly formed stereogenic center at C-2 of the amino acid moiety is the same as that in the proline moiety of the chiral auxiliary in the starting material. In reactions of the enolate of this chiral glycine

• . Bearing in mind that the starting materials are inexpensive and the chiral auxiliary is reusable (≥95% recovery), this protocol represents one of the best routes to the rather expensive (R)-allo-threonine (4). It is also possible to obtain (R)-allo-threonine starting from (R)-10 and acetaldehyde under

Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation

• Yiyang Liu,
• Marc Liniger,
• Ryan M. McFadden,
• Jenny L. Roizen,
• Jacquie Malette,
• Corey M. Reeves,
• Douglas C. Behenna,
• Masaki Seto,
• Jimin Kim,
• Justin T. Mohr,
• Scott C. Virgil and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2014, 10, 2501–2512, doi:10.3762/bjoc.10.261

• the natural product. Contrasting Meyers’ approach, which employed a chiral auxiliary as part of 39, we thought a catalytic enantioselective alkylation strategy would be ideal for a formal total synthesis of natural (−)-aspidospermine (36) via the antipode of 38. The formal synthesis began with 1,3

• using a chiral auxiliary strategy. We envisioned that chiral lactam 60 could again be readily accessed by our palladium-catalyzed enantioselective alkylation chemistry. The formal synthesis of (−)-vincadifformine commenced with ruthenium-catalyzed isomerization of the terminal olefin moiety in

• . Additionally, a rapid approach to a compound in Meyers’ formal synthesis of (+)-aspidospermine (36) granted access to the natural product without the use of a chiral auxiliary. Finally, we have demonstrated the application of lactam alkylation products in the catalytic asymmetric syntheses of (+)-rhazinilam

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• bearing the chiral auxiliary can be cleaved by ozonolysis to the corresponding aldehydes 36 and the latter reduced to alcohols 37, respectively, as shown in Scheme 4. Many highly functionalized, vicinally substituted compounds could be prepared by this method in good to excellent enantiopurity [37][38][39

• butenolide 83 in hand the stage was set for one of the key steps of the synthesis. Addition of the anion of phosphonamide 28c to 83 proceeded with a high level of facial and cis/trans-selectivity to afford adduct 88 as a single diastereomer with the correct stereochemistry. Removal of the chiral auxiliary by

• chiral auxiliary and oxidized to diacid 99. Converison into its potassium salt yielded squalene synthase inhibitor (S)-19. In a similar sequence, the minor diastereomer from the sulfuration, 1-epi 98, was converted into the opposite enantiomer (R)-19 (Scheme 12A). Reversing the steps for the introduction

Proton transfers in the Strecker reaction revealed by DFT calculations

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 1765–1774, doi:10.3762/bjoc.10.184

• asymmetric Strecker reaction, in which an (S)-α-phenylethylamine was employed as the chiral auxiliary [4]. In this reaction, he obtained a chiral alanine with 95% optically activity; see Scheme 2. In 1996, Lipton et al. succeeded in a series of asymmetric Strecker reactions by employing a chiral catalyst, a

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• (S)-4 to obtain 5, was achieved by treatment with N-methylpyrrolidine. An alternative method is based on ephedrine as a chiral auxiliary and was developed by Genêt and Jugé [36][37]. The key synthetic intermediates in this approach are 1,3,2-oxazaphospholidine boranes 7. These compounds are the

• for the synthesis of P-stereogenic phosphines by adding a catalytic amount of a chiral auxiliary. The enantioenriched phosphine 108 was obtained through coupling of racemic bulky secondary phosphine 107 with PhI in the presence of the base NaOSiMe3 and the Pd-catalyst (Scheme 30) [201]. In the

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

• Jian-bo Xie,
• Jian Luo,
• Timothy R. Winn,
• David B. Cordes and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 746–751, doi:10.3762/bjoc.10.69

• the treatment of multiple myeloma and mantle cell lymphoma [21]. This product is usually synthesized in three representative processes: (1) to use (1S,2S,3R,5S)-(+)-2,3-pinanediol as the chiral auxiliary for the addition reaction followed by chlorination and amination [14][15]; (2) to perform copper

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

• Yiwen Xiong,
• Haibo Mei,
• Lingmin Wu,
• Jianlin Han,
• Yi Pan and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 653–659, doi:10.3762/bjoc.10.57

• protected α-amino ester 4. Typical sulfinyl (a), phosphonyl aldimines (b) and phosphinyl imino esters (c). Synthesis of α-imino ester by rearrangement. Cleavage of the chiral auxiliary. Optimization of the synthesis of α-imino ester 3a by the condensation method.a Synthesis of N-phosphinyl-protected α-imino

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• , thioacetic acid and 4-methoxy-phenylethylamine (also as chiral auxiliary) provided the corresponding Ugi product 138 in 60% yield (dr 1:1). Chiral separation and deprotection in TFA resulted in compound 139 in 70% yield, after which saponification followed by an amide coupling with tryptamine and CDI

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• , as a chiral auxiliary it promotes the cycloaddition governing the stereochemistry of the process. The chiral auxiliary can be removed at the end of the reaction. Another interesting peculiarity concerns the exceptionally mild reaction conditions preventing unwanted aldehyde/enol or imine/enamine

Synthesis and stereochemical assignments of diastereomeric Ni(II) complexes of glycine Schiff base with (R)-2-(N-{2-[N-alkyl-N-(1-phenylethyl)amino]acetyl}amino)benzophenone; a case of configurationally stable stereogenic nitrogen

• Hiroki Moriwaki,
• Daniel Resch,
• Hengguang Li,
• Iwao Ojima,
• Ryosuke Takeda,
• José Luis Aceña and
• Vadim A. Soloshonok

Beilstein J. Org. Chem. 2014, 10, 442–448, doi:10.3762/bjoc.10.41

• novel and advanced structural type of Ni(II) complexes using an inexpensive and nonracemizable chiral auxiliary. As the first step in this direction, here we describe the preparation of Ni(II) complexes of glycine Schiff base with α-phenylethylamine-derived ligands. One unusual feature of these new

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes

• Ludovic Eberlin,
• Fabien Tripoteau,
• François Carreaux,
• Andrew Whiting and
• Bertrand Carboni

Beilstein J. Org. Chem. 2014, 10, 237–250, doi:10.3762/bjoc.10.19

• by using a chiral auxiliary (>95% de in the case of an L-proline-derived diene). Diversification on the different units, diene, dienophile and aldehyde, has been described. Concerning the maleimide material, substituent R3 did not exert any significant effect on the process. Other dienophiles have

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• [115][116], bearing a chiral auxiliary [117]. The intermediate cis-divinylcyclopropane 129 rearranged to the corresponding bridged cycloheptadiene 130 in a DVCPR. The chiral auxiliary was removed in the following using methanolysis conditions, followed by reduction of the more electron rich double bond

• towards the total synthesis of salvileucalin B (292, see Scheme 35) isolated from the plant Salvia leucantha [213]. Starting from enantiopure trialkyne 282, desilylation was affected using TBAF, followed by ruthenium-catalyzed cycloisomerization [214] and cleavage of the chiral auxiliary to obtain