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Search for "stereoselectivity" in Full Text gives 406 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
A concise and practical stereoselective synthesis of ipragliflozin L-proline
Beilstein J. Org. Chem. 2017, 13, 1064–1070, doi:10.3762/bjoc.13.105
- Negishi cross-coupling of arylzinc with protected glycosyl bromide in the presence of Ni-catalysts. An improved procedure with high stereoselectivity and in the absence of catalysts was reported subsequently by Lemarie et al. (Scheme 1) [12] to construct the anomeric chiral center of dapagliflozin and
- was developed. The route initiated from compound 4a and pivaloyl-protected glycosyl bromide 2b, the β-C-arylglucoside 5 was obtained with high stereoselectivity in one step after a halogen–lithium exchange/transmetalation/coupling sequence. Cryogenic temperatures and catalysts were not required. The
Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes
Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73
- oligomerization [55][56] competitive reactions. In addition, whenever an internal alkyne is to be hydrogenated, stereoselectivity must also be considered [57] (Scheme 1). The main byproduct usually obtained is the over-hydrogenation one, which results in conversion and selectivity to be inversely proportional
- challenging and intriguing owing to the stereoselectivity involved (usually cis) and to the large use of the products thereof in the fine-chemical industry. Most significant substrates examined in the literature under the continuous-flow catalysis conditions are reported in Scheme 3. 3-Hexyne Analogously to
(Z)-Selective Takai olefination of salicylaldehydes
Beilstein J. Org. Chem. 2017, 13, 323–328, doi:10.3762/bjoc.13.35
- led to the identification of key factors responsible for this surprising inversion of selectivity, and enabled the development of a modified mechanistic model to rationalise these observations. Keywords: alkenyl iodides; salicylaldehydes; stereoselectivity; Takai olefination; transition state
- )-stereoselectivity observed in the chromium(II)-mediated homologation of aldehydes to alkenes (including vinyl halides). The salient features of both models are the same (Scheme 2). It is presumed that the addition of the gem-dichromium species 3 to the aldehyde 1 proceeds via a six-membered pseudo-chair transition
- clarity. An unusually high level of (Z)-stereoselectivity was observed in the Takai olefination of 6. (E):(Z)-ratio determined by 1H NMR analysis of crude material obtained after reaction work-up. See Supporting Information File 1 for more information. Takai olefination of meta-hydroxybenzaldehyde. Yield
NMR reaction monitoring in flow synthesis
Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31
- including DEPT spectra, 2D-NMR spectroscopy, 19F NMR spectroscopy and monitoring of the stereoselectivity in Diels–Alder reactions and self-optimization of flow conditions using a modified version of the Nelder–Mead algorithm. For the NMR integral data for each experiment, the algorithm (Figure 15) selects
Efficient access to β-vinylporphyrin derivatives via palladium cross coupling of β-bromoporphyrins with N-tosylhydrazones
Beilstein J. Org. Chem. 2017, 13, 195–202, doi:10.3762/bjoc.13.22
- features – stoichiometric organometallic reagents are not required for the coupling reaction and di- and trisubstituted olefins can be prepared with high stereoselectivity. In fact, N-tosylhydrazones used in this methodology can be easily prepared from carbonyl compounds (Scheme 1), as it has been well
Silyl-protective groups influencing the reactivity and selectivity in glycosylations
Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12
- or high stereoselectivity. This mini review will summarize these findings. Keywords: Carbohydrate; conformation; glycosylation; reactivity; selectivity; Introduction Silicon-based protective groups of alcohols have a long history in organic chemistry [1][2][3]. The most popular and commercially
- acceptors. However, glycosylation with heavily silylated carbohydrate derivatives is comparatively new, and so is the significance that silyl groups have on the stereoselectivity and reactivity in glycosylation reactions [4]. These findings, which most have occurred in the last decade, will be reviewed here
- excess donor in diethyl ether since this gave the best α-selectivity (Scheme 2). Using other protective groups on the fucose part, such as 2,3-TIPDS and 4-O-TES led to glycosylation with only poor stereoselectivity [8]. The TES groups were also used successfully on the 2-methylamino analogue of 4. A
Strategies in asymmetric catalysis
Beilstein J. Org. Chem. 2017, 13, 63–64, doi:10.3762/bjoc.13.8
- Tehshik P. Yoon Department of Chemistry, University of Wisconsin–Madison, 1101 University Avenue, Madison, WI 53706, USA 10.3762/bjoc.13.8 Keywords: asymmetric catalysis; enantioselectivity; stereoselectivity; The stereochemistry of an organic compound can have a profound influence on many of
Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates
Beilstein J. Org. Chem. 2017, 13, 33–42, doi:10.3762/bjoc.13.5
- preference for either d, l or meso had been observed [35], proving this precondition to be legitimate. Comparing the stereoselectivity in the homo- and hetero-coupling reaction (Table 3), a slightly better selectivity is observed for the homo-coupling reaction. This is probably due to the bulkier coradical
First DMAP-mediated direct conversion of Morita–Baylis–Hillman alcohols into γ-ketoallylphosphonates: Synthesis of γ-aminoallylphosphonates
Beilstein J. Org. Chem. 2016, 12, 2906–2915, doi:10.3762/bjoc.12.290
- gave the corresponding primary allylphosphonates 4d–f with a high Z-stereoselectivity (Z/E = 87–100/13–0) and in 56–92% yields (Table 2, entries 5–7). It seems that the Z/E ratios depend on the nature of the R allylic group. Indeed, when it is an alkyl group, i.e., R1 = Me, the phosphonates 4d and 4e
cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin
Beilstein J. Org. Chem. 2016, 12, 2816–2822, doi:10.3762/bjoc.12.280
- the synthesis of carbo- and heterocyclic compounds [21][22][23][24]. The easy accessibility of racemic and enantiomerically pure epoxy substrates through a number of well-established epoxidation methods coupled with procedural simplicity, high atom economy, regio- and stereoselectivity of IFCEA
Synthesis of spiro[isoindole-1,5’-isoxazolidin]-3(2H)-ones as potential inhibitors of the MDM2-p53 interaction
Beilstein J. Org. Chem. 2016, 12, 2793–2807, doi:10.3762/bjoc.12.278
- -benzylnitrone with isoindolin-3-methylene-1-ones. The regio- and stereoselectivity of the process have been rationalized by computational methods. The obtained compounds show cytotoxic properties and antiproliferative activity in the range of 9–22 μM. Biological tests suggest that the antitumor activity could
- complete regioselectivity and a high stereoselectivity in favour of the [1(RS),4’(RS)]2,2’-dibenzyl-4’-substituted spiro[isoindole-1,5’-isoxazolidin]-3(2H)-ones 6a–f. The structure of adducts 6 and 7 has been elucidated by 1H NMR and 13C NMR spectroscopies and MS spectrometry. In particular, the 1H NMR
Towards the development of continuous, organocatalytic, and stereoselective reactions in deep eutectic solvents
Beilstein J. Org. Chem. 2016, 12, 2620–2626, doi:10.3762/bjoc.12.258
- synthesis of enantiomerically enriched products by testing different experimental set-ups. L-Proline-catalysed cross-aldol reactions were efficiently performed in continuo, with high yield (99%), anti-stereoselectivity, and enantioselectivity (up to 97% ee). Moreover, using two different DES mixtures, the
- use of any organic solvent by a proper choice of DES components. The dramatic influence of the reaction media on the reaction rate and stereoselectivity of the process suggests that the intimate architecture of DESs deeply influences the reactivity of different species involved in the catalytic cycle
- chiral products [2]. Among all the possible options, the L-proline-catalysed stereoselective cross-aldol reaction remains the greener choice. After the pioneering works by List and Barbas [3], a huge effort was made by the scientific community to improve both the yield and the stereoselectivity of the
Catalytic Wittig and aza-Wittig reactions
Beilstein J. Org. Chem. 2016, 12, 2577–2587, doi:10.3762/bjoc.12.253
- reaction (Scheme 8) [22]. This reaction involved the intramolecular cyclization of 27 to form 28. A variety of phosphines were examined as the catalyst, and (S,S)-29 ((S,S)-Me-DuPhos, 0.1 equivalent) was found to provide the best combination of reactivity and stereoselectivity (39% yield, 62% ee). In these
Biomimetic synthesis and HPLC–ECD analysis of the isomers of dracocephins A and B
Beilstein J. Org. Chem. 2016, 12, 2523–2534, doi:10.3762/bjoc.12.247
- arises from the amidocarbinol ether (±)-9 after protonation and loss of ethanol. The planar structure of the cation explains the lack of stereoselectivity observed in the reaction. Physicochemical measurements Physicochemical characterization of dracocephins A and B was also carried out. The relevant
Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides
Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233
- , driven by the higher stability of the former, apparently controls the stereoselectivity of the investigated cycloaddition reaction with benzonitrilе oxide. Based on the reactivity of azolyl enamines towards hydroxamoyl chlorides, a novel, effective catalyst-free method was elaborated to prepare 4-azolyl
- stereoselectivity for this reaction is lacking from the literature. To the best of our knowledge there are no examples for the synthesis of 4-isoxazolyl- and imidazolylisoxazoles and imidazolylisoxazolines by this reaction. We report here the results of experimental and theoretical studies for the reaction of β
- observed reaction rate increase when an electron-withdrawing group is introduced to the structure of nitrile oxide. Thus, according to calculations, reaction of enamines with nitrile oxides leading to isoxazolines, complies to cycloaddition with inverse electron-demand. The observed stereoselectivity of
Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route
Beilstein J. Org. Chem. 2016, 12, 2343–2350, doi:10.3762/bjoc.12.227
- stereoselectivity in accordance with the predicted stereo-outcome. In this way, the orthogonal protecting groups (allyl and naphthalenylmethyl) installed on aldohexos-5-ulose 20, differentiated the two 1,2-cis hydroxy couples (2,3 and 4,5 positions) of 22 which can be easily transformed further in a selective
Highly chemo-, enantio-, and diastereoselective [4 + 2] cycloaddition of 5H-thiazol-4-ones with N-itaconimides
Beilstein J. Org. Chem. 2016, 12, 2293–2297, doi:10.3762/bjoc.12.222
- devised and demonstrated as a competent catalyst to furnish excellent chemo- and stereoselectivity [10]. Therefore, we examined catalyst III for this reaction (Table 1, entry 3); annulation adduct 3a was obtained in 60% yield with 70% ee. The increased in enantioselectivity indicates the potential of
Stereoselective synthesis of fused tetrahydroquinazolines through one-pot double [3 + 2] dipolar cycloadditions followed by [5 + 1] annulation
Beilstein J. Org. Chem. 2016, 12, 2204–2210, doi:10.3762/bjoc.12.211
- associated with these substrates. The stereochemistry of 7h has been determined by X-ray single crystal structure analysis (Figure 3). As mentioned previously, the stereoselectivity of the first [3 + 2] cycloaddition for compounds 2 has been well reported [22][23][24][25][26][27]. The mechanism for the
The direct oxidative diene cyclization and related reactions in natural product synthesis
Beilstein J. Org. Chem. 2016, 12, 2104–2123, doi:10.3762/bjoc.12.200
- ) THF (3 in Scheme 1, the general structure of which is today often as a simplification referred to as “THF diol”) [8]. In addition, they found that this reaction proceeds with high stereoselectivity (vide infra) and demonstrated that the reaction is not only limited to terpenes such as geranyl- (1b, R
- = Ac) or neryl acetate but seemed to be fairly general to other 1,5-diene substrates. Finally, they speculated on possible intermediates which may account for the outcome and the overall stereoselectivity of this unusual reaction. A mechanism, however, was not provided (vide infra). To date it is
- are Re(VII), Cr(VI) and Co(II) complexes [26][27][28][29]. Again, the observed efficiency and stereoselectivity for this class of oxidative cyclization reactions is high. Another set of substrates are 5-hydroxyalkenes, starting materials, completely lacking the 6-OH-group (or ether oxygen donor
Chiral ammonium betaine-catalyzed asymmetric Mannich-type reaction of oxindoles
Beilstein J. Org. Chem. 2016, 12, 2099–2103, doi:10.3762/bjoc.12.199
- % without sacrificing reaction efficiency (Table 1, entry 7). It is noteworthy that the present system is scalable; the reaction with 1.0 g of 2a reached completion within 20 h to afford 4aa with a similar degree of stereoselectivity (Table 1, entry 8), and subsequent recrystallization furnished 0.83 g of
Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes
Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184
- many biologically interesting molecules due to the diverse opportunities created by subsequent transformations of the resulting 1,2-oxazine ring. This review discusses the rationale for the observed regio- and stereoselectivity and the methods developed in recent years used to control and improve the
- stereo- and regioselectivity for the synthesis of 1,2-oxazine scaffolds. Keywords: diene; hetero-Diels–Alder; nitroso compounds; regioselectivity; stereoselectivity; Review Introduction The hetero-Diels–Alder reaction represents one of the most important methods in organic synthesis, providing various
- , none of these reviews focused on general aspects of the regio- and stereoselectivity of the nitroso hetero-Diels–Alder reaction and the possibility of its control. These aspects were partially covered in a review by Yamamoto in 2006 [27], which focused on asymmetric nitroso hetero-Diels–Alder reactions
A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis
Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176
- moderate stereoselectivity is superimposed with a kinetic resolution of enantiomers in the subsequent retro-aldol reaction. Both are catalyzed by the chiral guanidine 10. As a result, the numbers shown in Table 1 are not constant but depend on the relative turnover of each reaction. When rac-25 reacted
- secondary conversion occurs. In contrast, when compound 21 reacts with 24 ring opening is so fast that no Diels–Alder product accumulates. Here the ee value of the Michael product 31 (21%) must correspond to the stereoselectivity of the Diels–Alder step. Due to low stereoselectivities and fast retro-aldol
- the six-membered structure of 10 does not increase the stereoselectivity when it is used as a catalyst. We could not observe the near-perfect selectivities of the Tan catalyst 8 in the base-induced reaction of anthrones and maleimides. Nevertheless ee values of up to 83% for the formal Michael
TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals
Beilstein J. Org. Chem. 2016, 12, 1758–1764, doi:10.3762/bjoc.12.164
- [4], and were recently observed to inhibit cancer growth [5]. Because of the relevance of 2-deoxyglycosides, great efforts have been made in researching the assembly of oligosaccharides containing these sugars [6][7]. However, the absence of a neighbouring group at C2 causes poor stereoselectivity
- functionalities at C6 [10][38][39][40][41][42] have also been developed to improve the stereoselectivity. However, additional required steps involving the introduction and removal of directing groups are reducing the efficiency. Thioglycosides are some of the most commonly used donors for glycosylation reactions
- , entries 2–6). For per-O-benzylated glucal (3) and per-O-acetylated rhamnal (5), the corresponding thiol-2-deoxyglycosides 7 (61%, α:β = 2:1) and 10 (76%, α:β = 2:1) were produced in good yields with moderate stereoselectivity (Table 1, entry 2 and 5). Interestingly, as shown in Table 1, entries 1 and 2
Rearrangements of organic peroxides and related processes
Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162
Experimental and theoretical insights in the alkene–arene intramolecular π-stacking interaction
Beilstein J. Org. Chem. 2016, 12, 1616–1623, doi:10.3762/bjoc.12.158
- diastereoselective as predicted by the Alder´s rule. The reaction between 6a or 6b and cyclopentadiene carried out at room temperature showed a high stereoselectivity (Table 2, entries 1 and 3, respectively). These results are similar to the ones previously reported for 6c (endo R/S 13:87) [16]. Noticeably, the endo
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