Confirmation of the stereochemistry of spiroviolene

• Yao Kong,
• Yuanning Liu,
• Kaibiao Wang,
• Tao Wang,
• Chen Wang,
• Ben Ai,
• Hongli Jia,
• Guohui Pan,
• Min Yin and
• Zhengren Xu

Beilstein J. Org. Chem. 2024, 20, 852–858, doi:10.3762/bjoc.20.77

• Abstract We confirm the previously revised stereochemistry of spiroviolene by X-ray crystallographically characterizing a hydrazone derivative of 9-oxospiroviolane, which is synthesized by hydroboration/oxidation of spiroviolene followed by oxidation of the resultant hydroxy group. An unexpected thermal

• hydroxy group, or a keto group) for further derivatization. Spiroviolene was not transformed when subjected to conditions for allylic oxidation (SeO2) even at elevated temperature [27], and the starting material was fully recovered. We have also tried hydroboration/oxidation conditions for transforming

• detailed analysis of the NMR spectra, we have found that besides the normal hydroboration/oxidation product 1α-hydroxyspiroviolane (9), 9α- (10) and 9β-hydroxyspiroviolane (11) resulting from a formal boration at the homoallylic C9 position were also produced. The stereochemistry of the newly generated

Total synthesis of grayanane natural products

• Nicolas Fay,
• Rémi Blieck,
• Cyrille Kouklovsky and
• Aurélien de la Torre

Beilstein J. Org. Chem. 2022, 18, 1707–1719, doi:10.3762/bjoc.18.181

• the PMB protecting group, Dess–Martin oxidation, and SmI2-induced cyclization. This last step was highly selective, giving solely the intermediate 17. The synthesis was then pursued by the hydroboration–oxidation of the monosubstituted alkene, followed by stereoselective epoxidation of the 1,1

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• isoxazolidin-4-ols. The strategy relies on a highly regio- and trans-stereoselective hydroboration–oxidation reaction of the 4,5-unsubstituted 2,3-dihydroisoxazoles with basic hydrogen peroxide. The consecutive oxidation/reduction route, sequentially employing Dess–Martin periodinane and ʟ-selectride, is used

• -hydroxypyrrolidines certainly makes the 4-hydroxyisoxazolidines important and valuable structural fragments in drug discovery. Keywords: 2,3-dihydroisoxazoles; diastereoselectivity; heterocycles; hydroboration–oxidation; isoxazolidin-4-ols; Introduction 2,3-Dihydroisoxazoles (often referred to as 4-isoxazolines

• alcohols. As a consequence, we assumed that the hydroboration–oxidation reaction of 2,3-dihydroisoxazoles would be an excellent way to prevent this obstacle. Recently, Kang et al. [29] reported the first hydroboration–oxidation reaction of the 5-substituted 4-isoxazolines even though the access to 4

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• ]-sigmatropic rearrangement of allyldiphenylphosphinites, obtained from (1R,2R,4S,5R)-3-methyleneneoisoverbanol and (1R,2R,3R,5R)-4-methyleneneoisopinocampheol, to allylphosphine oxides. Hydroxy groups were introduced stereoselectively through a hydroboration–oxidation reaction proceeding from the less hindered

• % yield. The allylic diphenylphosphine oxide 21 was subjected to the hydroboration–oxidation reaction introducing stereoselectively the hydroxy group. Hydroboration was carried out with an excess of borane–dimethyl sulfide adduct followed by the oxidation step. The standard C–B bond oxidation protocol

• -methyleneneoisopinocampheol were synthesized using known procedures. They were used in the key transformation, the thermal [2,3]-sigmatropic rearrangement of allyldiphenylphosphinites to allyldiphenylphosphine oxides. Allylphosphine oxides were further functionalized through a hydroboration–oxidation reaction occurring from

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

• ), giving allyl ketone (−)-18 in 94% yield and 91% ee [34]. Treatment of the ketone (−)-18 with MeMgBr at 23 ºC provided a mixture of two diastereomeric alcohols 19A and 19B in 94% yield. Without separation, the diastereomers were rapidly carried through a three-step sequence of hydroboration/oxidation

Addition of H-phosphonates to quinine-derived carbonyl compounds. An unexpected C9 phosphonate–phosphate rearrangement and tandem intramolecular piperidine elimination

• Łukasz Górecki,
• Artur Mucha and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 883–889, doi:10.3762/bjoc.10.85

• (R/S). The homologous aldehyde can be prepared by oxidation of the double bond in a hydroboration–oxidation sequence, however, the presence of the nitrogen atoms, particularly that of the tertiary amino group of quinuclidine, may be troubleshooting [28][29]. Borane complexes with heteroaromatic and

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

• Dae Won Cho,
• Patrick S. Mariano and
• Ung Chan Yoon

Beilstein J. Org. Chem. 2014, 10, 514–527, doi:10.3762/bjoc.10.47

• into the amidols 69 can be easily achieved by employing Lewis acid-catalyzed reactions with allyltrimethylsilane, which produce the allylation products 71. Hydroboration–oxidation of the terminal olefin moieties in 71 then forms the corresponding alcohols 70 that contain key hydroxypropyl side chains

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

• yielded intermediate cis-divinylcyclopropane 164, which underwent the desired rearrangement at remarkably low temperature to yield bicycle 165. Selective hydroboration/oxidation (directed through participation of the untouched double bond) followed by Swern oxidation gave ketone 166. The enone system 167

• was prepared through addition of Eschenmoser’s salt, followed by Hoffman elimination of the resulting amine. Luche reduction [143] from the less hindered side followed by hydroboration/oxidation gave diol 168. Mono-mesylation of the primary alcohol followed by the addition of base furnished the

• synthesis of the diterpene scopadulcic acid B (79, see Scheme 10), isolated from the Paraguayan plant Scoparia dulcis [66]. Starting from 2-iodobenzaldehyde (65) allyl-Grignard addition took place followed by TBS-protection of the resulting alcohol. The installed double bond was subjected to hydroboration

Cyclopamine analogs bearing exocyclic methylenes are highly potent and acid-stable inhibitors of hedgehog signaling

• Johann Moschner,
• Anna Chentsova,
• Nicole Eilert,
• Irene Rovardi,
• Philipp Heretsch and
• Athanassios Giannis

Beilstein J. Org. Chem. 2013, 9, 2328–2335, doi:10.3762/bjoc.9.267

• , 0 °C, 93%), (2) hydroboration/oxidation (9-BBN, THF, 70 °C; then NaBO3, H2O, 50 °C, 91%) and finally, (3) oxidative cyclization (BAIB, cat. TEMPO, CH2Cl2, 25 °C, 73%) was employed. Deprotection of the silyl ether (HF, MeCN, 25 °C, 87%) and base-induced rearrangement of the steroid skeleton via the

Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

• Todd J. Eckroat,
• Abdelrahman S. Mayhoub and
• Sylvie Garneau-Tsodikova

Beilstein J. Org. Chem. 2013, 9, 1012–1044, doi:10.3762/bjoc.9.116

• imidazopyridine, [18F]FPPIP (142), was prepared starting from 140e. A palladium-catalyzed coupling with tributyl(vinyl)tin to give an alkene intermediate was followed by hydroboration-oxidation to give the hydroxypropyl intermediate 145, which was radiolabeled to give 142 (Scheme 10B). This compound showed good

Methylidynetrisphosphonates: Promising C₁ building block for the design of phosphate mimetics

• Vadim D. Romanenko and
• Valery P. Kukhar

Beilstein J. Org. Chem. 2013, 9, 991–1001, doi:10.3762/bjoc.9.114

• . Reaction between tert-butylphosphaethyne and diethyl phosphite in the presence of sodium metal. Cross metathesis of trisphosphonates 12 with 2-methyl-2-butene and the Grubbs second-generation catalyst. Hydroboration–oxidation of trisphosphonates 12b,e. Reaction of 3-butyn-1-ylidenetrisphosphonate 15 with

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• ], the introduction of an additional hydroxyl moiety into 1,2-oxazine derivatives was an essential goal in several studies by our group [34][46][47][48]. A series of 5-hydroxy-1,2-oxazine derivatives was successfully prepared by the well known hydroboration/oxidation protocol, with yields and

• the observed diastereoselectivities. All products 6–11 obtained by the hydroboration/oxidation protocol were easily purified and separated by column chromatography and finally deprotected by treatment with acid. This afforded a series of the desired, highly functionalised tetrahydro-2H-1,2-oxazine

• -derived nitrone 1a leading to 3,6-dihydro-2H-1,2-oxazine derivatives 3 via the respective N-hydroxylamines 2. Speculative mechanistic suggestion for the formation of tetrasubstituted pyrrole derivative 5. Introduction of a 5-hydroxy group into 1,2-oxazine derivatives 3 by a hydroboration/oxidation

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• /hydroboration/oxidation, which gave the best results when the Hoveyda–Grubbs catalyst 6 was used in the RCM (Scheme 15). Interestingly, in this case the asymmetric synthesis of the protected RCM precursor 78 started from a non-chiral source, the alcohol 75, and proceeded with complete stereocontrol over the 11

• %; in refluxing toluene) 79 was obtained in 85% yield. The three reaction steps leading from 78 to 80, i.e., RCM/hydroboration/oxidation, could be accomplished in one-pot to afford the product as a single isomer (all-trans triol). The prepared (+)-1-deoxynojirimycin (62) displayed spectroscopic data

Enantioselective synthesis of tricyclic amino acid derivatives based on a rigid 4-azatricyclo[5.2.1.0^2,6]decane skeleton

• Matthias Breuning,
• Tobias Häuser,
• Christian Mehler,
• Christian Däschlein,
• Carsten Strohmann,
• Andreas Oechsner and
• Holger Braunschweig

Beilstein J. Org. Chem. 2009, 5, No. 81, doi:10.3762/bjoc.5.81

• racemic form starting from inexpensive endo-carbic anhydride (10, Scheme 1). Conversion of the succinyl anhydride moiety in 10 into the pyrrolidine ring in 11 was accomplished in three steps and 74% yield by imide formation, reduction [24], and N-protection. Hydroboration/oxidation of the alkene function

• oxidation of the alkene rac-13 (Scheme 3), which was available from the ketone rac-9 either by Wittig reaction or by a Tebbe-type olefination [31] using Mg, TiCl4, and CH2Cl2. Hydroboration/oxidation of rac-13 occurred highly diastereoselectively on the exo-side providing the desired endo-alcohol rac-14, as

Radical cascades using enantioenriched 7-azabenzonorbornenes and their applications in synthesis

• David M. Hodgson and
• Leonard H. Winning

Beilstein J. Org. Chem. 2008, 4, No. 38, doi:10.3762/bjoc.4.38

• radical systems. Deoxygenation-rearrangement-electrophile trapping. Asymmetric hydroboration–oxidation of alkenes 14, 16 and 18. Deoxygenation–rearrangement–isomerisation of xanthates 20 and 23. Deoxygenation–rearrangement–electrophile trapping of xanthates 20 and 23. 2-Azabenzonorbornene as a masked

• acrylate (Figure 2), was subject to the same conditions as azacycle (+)-8 and was found to give trisubstituted pyrrolidine 36, in 23% yield (Scheme 8). Although the yields for these reactions were modest, access to pyrrolidine (+)-35 allowed the absolute sense of asymmetric induction in the hydroboration

• –oxidation with (−)-Ipc2BH to be determined by chemical correlation. Pyrrolidine 35 was independently prepared from (1R)-(−)-2-azabicyclo[2.2.1]hept-5-en-3-one (Vince’s lactam [36], 37) via reduction with LiAlH4, Boc-protection and oxidative cleavage [37] (Scheme 9). The pyrrolidines prepared from rearranged