Ene–yne cross-metathesis with ruthenium carbene catalysts

• Cédric Fischmeister and
• Christian Bruneau

Beilstein J. Org. Chem. 2011, 7, 156–166, doi:10.3762/bjoc.7.22

• , whereas a 1,2-relationship was observed starting from internal alkynes (Scheme 9) [62][63]. In addition, the stereoselectivity was low in the first case (3:1) and a single regio- and stereoisomer was obtained from internal alkynes. The regioselectivity was proposed to originate from the steric and

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• Grignard from which the organocopper compound was prepared (Scheme 20) [46][47][48][49][50]. Excess of copper salt provides a better stereoisomeric ratio (>90%) [46]. Only the addition of t-BuCu gave a single stereoisomer [51]. In contrast, the copper-catalyzed carbozincation reaction led to a single

• stereoisomer via syn addition under mild conditions in either THF or Et2O (Scheme 20) and the reaction could be expanded to incorporate a large variety of functionalized alkylzinc bromide and dialkylzinc species [52]. Copper-catalyzed carbozincation could also be performed under very different conditions

• (toluene, reflux) and a single isomer was still obtained [53]. 1-Alkynyl sulfoximines behave similarly to alkynyl sulfones and the addition of an organocopper reagent usually leads to two isomers in variable amounts. Copper-catalyzed carbozincation to give a single regio- and stereoisomer in excellent

Prins fluorination cyclisations: Preparation of 4-fluoro-pyran and -piperidine heterocycles

• Guillaume G. Launay,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2010, 6, No. 41, doi:10.3762/bjoc.6.41

• determined and the syn-stereoisomer 9b, as shown in Figure 2, was confirmed as the major product of this Prins reaction. It is interesting to note that when (E)- and (Z)-hex-3-en-1-ol (11a) and (11b) were used as substrates, the double bond stereochemistry is retained. Only two diastereoisomers were observed

Synthesis of (3R,5R)-harzialactone A and its (3R,5S)-isomer

• Gowravaram Sabitha,
• Rangavajjula Srinivas,
• Sukant K. Das and
• Jhillu S. Yadav

Beilstein J. Org. Chem. 2010, 6, No. 8, doi:10.3762/bjoc.6.8

• . Epoxide opening with thioacetal and diastereoselective reductions are used as key reactions. Keywords: dithiane; harzialactone A; hydroxyl directed reduction; stereoisomer; Introduction Marine microorganisms such as bacteria, fungi, and microalgae have proved to be a rich source of structurally novel

• the major product, which was converted into stereoisomer (3R,5S)-2 via acetonide 12, deprotection of benzyl group to give 13, and further functional group transformations by use of the same reagents and conditions as those described for the conversion of 10 into 1. The IR absorption at 1775 cm−1

• carbon in the downfield region (100.5 ppm) [7]. In conclusion, a stereoselective synthesis of natural (+)-(3R,5R)-harzialactone A and its nonnatural stereoisomer (3R,5S) has been accomplished. Natural harzialactone A (1), and its (3R,5S)-isomer (2). Retrosynthesis of harzialactone A (1). Synthesis of

Three step synthesis of single diastereoisomers of the vicinal trifluoro motif

• Vincent A. Brunet,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2009, 5, No. 61, doi:10.3762/bjoc.5.61

• absolute configuration (Figure 1). Generation of the syn-α,β-epoxy alcohols Aa was more challenging. This stereoisomer will ultimately deliver the all-syn Da trifluoro motif (Scheme 1). Epoxidation of (S)-5 with L-DIPT showed poor stereoselectivity and under optimised conditions the resultant α,β-epoxy

• diastereoisomeric series. Reaction of α,β-epoxy alcohol 7b with Deoxo-Fluor® also proceeded smoothly generating fluoro epoxide (2S,3S,4R)-9b in 95% yield and as a single stereoisomer. However when 9b was treated with HF/pyridine [19][20] there was no evidence that the expected difluoro alcohol 12b had formed

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• 2004, Curran’s group [55] reported a 4-mix/4-split strategy for the synthesis of a stereoisomer library of (+)-murisolin and 15 of its isomers, which relied on solution phase technique of fluorous mixture synthesis (Scheme 17). In their synthetic route, a single mixture of M-119, which was tagged with

• InCl3 in the presence of aldehyde 218a afforded the expected anti-adduct 220. Addition of stannane 222 to aldehyde 221 in the presence of BF3·OEt2 afforded the syn-adduct 223 as the only detectable stereoisomer. Tosylation of the alcohol followed by exposure to TBAF promoted bis-THF cyclization

Diastereoselective and enantioselective reduction of tetralin- 1,4-dione

• E. Peter Kündig and
• Alvaro Enriquez-Garcia

Beilstein J. Org. Chem. 2008, 4, No. 37, doi:10.3762/bjoc.4.37

• reduction of dione 2 was probed next. This was carried out successfully as shown in Scheme 4 and gave, after two recrystallizations from diisopropylether, (−)-(1R,4R)-tetralin-1,4-diol (R,R-7) in 72% yield and 99% ee [8]. Only small amounts (ca. 7%) of the cis stereoisomer 6 were detected by 1H NMR in the

Total synthesis of the indolizidine alkaloid tashiromine

• Stephen P. Marsden and
• Alison D. McElhinney

Beilstein J. Org. Chem. 2008, 4, No. 8, doi:10.1186/1860-5397-4-8

• ). The absolute stereochemistry of the newly established asymmetric centres would be controlled by allylic strain arguments, assuming that the well-established precedent for anti-SE2’ attack of the iminium on the allylsilane was upheld here [40]. Thus, the predicted major stereoisomer 10 would have (5S

The use of chiral lithium amides in the desymmetrisation of N-trialkylsilyl dimethyl sulfoximines

• Matthew J. McGrath and
• Carsten Bolm

Beilstein J. Org. Chem. 2007, 3, No. 33, doi:10.1186/1860-5397-3-33

• values which are calculated from the 1H NMR spectra of diastereomeric amides, prepared by coupling a single sulfoximine stereoisomer separately with both enantiomers of O-methyl mandelic acid. They found that the difference in chemical shift between the methyl groups of (R,S)-13 and S-(R) isobutyl methyl

Reactions of glycidyl derivatives with ambident nucleophiles; part 2: amino acid derivatives

• Gerald Dyker,
• Andreas Thöne and
• Gerald Henkel

Beilstein J. Org. Chem. 2007, 3, No. 28, doi:10.1186/1860-5397-3-28

• from a weak intramolecular hydrogen bond. According to ab initio calculations for cis-9a, (B3LYP, 6-31G*, zero point energy included) this structure is indeed 1.9 kcal/mol more stable than its exo-oriented conformer and 2.2 kcal/mol more stable than its trans-stereoisomer. Conclusion In summary, we

8-epi-Salvinorin B: crystal structure and affinity at the κ opioid receptor

• Thomas A. Munro,
• Katharine K. Duncan,
• Richard J. Staples,
• Wei Xu,
• Lee-Yuan Liu-Chen,
• Cécile Béguin,
• William A. Carlezon Jr. and
• Bruce M. Cohen

Beilstein J. Org. Chem. 2007, 3, No. 1, doi:10.1186/1860-5397-3-1

• mania.[4][5][10] Salvinorins tend to isomerize under basic conditions. Valdés reported that borohydride reduction of 1a gave an unidentified stereoisomeric byproduct, which could be converted to an undetermined stereoisomer of 1a.[11] The latter compound was subsequently identified by Brown as 8-epi

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• formation of 19 also in a 4:1 ratio of diastereoisomers. Erythro 2,3-difluorosuccinic acid 19 was obtained in a modest yield as a single stereoisomer from a stereochemically pure sample of the erythro 13. A crystal of erythro-19 suitable for X-ray analysis was obtained after sublimation, and the resultant

• and reinforces earlier studies on the conformation of vicinal difluoro compounds. This is in line with the well described fluorine gauche effect. The only exception to this was found for the threo stereoisomer of 1,2-difluoro-1,2-diphenylethanes 13, where all of the data (ab initio, NMR and X-ray) did

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• generate 16 and 17 as homochiral materials. The major diastereoisomer 16, was then subjected to iodolactonization and this resulted in a stereoisomer mixture of (3S, 5S)-12 and (3S, 5R)-13 in a ratio of 9.4:1 (Scheme 4). Interestingly iodolactonisation of 17 gave a single product (3R, 5R)-12 ([α]D = +16

• substrate. Accordingly allyl pyrrolidine 23 was treated with 2-fluoropropionyl chloride in the presence of Hünig's base and Yb(OTf)3. This generated product 24 as a single stereoisomer. Reduction of Lewis acid from 1.0 to 0.5 eq did not adversely effect the diastereoselectivity, however a stoichiometry

• lower than 0.5 eq did compromise the stereoselectivity of the reaction. An analogous reaction with 2-fluorophenylacetyl chloride generated 25, also as a single stereoisomer. Clearly the co-ordination of the Lewis acid to the ether oxygen is exerting full stereochemical control on the reaction. This is a

Synthesis and glycosidase inhibitory activity of new hexa- substituted C8-glycomimetics

• Olivia Andriuzzi,
• Christine Gravier-Pelletier,
• Gildas Bertho,
• Thierry Prangé and
• Yves Le Merrer

Beilstein J. Org. Chem. 2005, 1, No. 12, doi:10.1186/1860-5397-1-12

• presence of N-methylmorpholine oxide and tert-butanol cleanly led to the expected cis-diol 3 in 97% yield. In analogous manner, the D-manno-cyclooctene 2 gave the corresponding cis-diol 4 in 97% yield. In each case, the cis-diol 3 or 4 has been isolated as a single stereoisomer because of the C2-axis of

• and 2 the cis-epoxide 7 or 8 has been isolated as a single stereoisomer. However, all attempts to open the epoxide ring involving various nucleophiles, sodium azide, benzylamine, n-butylamine, or serinol in different experimental conditions, protic or aprotic solvent, presence or absence of a Lewis

Mixtures of monodentate P-ligands as a means to control the diastereoselectivity in Rh-catalyzed hydrogenation of chiral alkenes

• Manfred T. Reetz and
• Hongchao Guo

Beilstein J. Org. Chem. 2005, 1, No. 3, doi:10.1186/1860-5397-1-3

• even two stereogenic centers. Ligands P18, P20 and P21[32] were used in the (S)-form. In the case of the menthyl-derivative P15, a single stereoisomer was employed, although the configuration at phosphorus is unknown.[33] The menthol-derived ligand P23 having the (S)-configuration at phosphorus was