A concise enantioselective synthesis of the guaiane sesquiterpene (−)-oxyphyllol

• Martin Zahel and
• Peter Metz

Beilstein J. Org. Chem. 2013, 9, 2028–2032, doi:10.3762/bjoc.9.239

• shown in Scheme 2, we first planned to use the known diol 7, which is available by diastereoselective dihydroxylation of 4 [6]. Since a chemoselective deoxygenation of the secondary alcohol of 7 would give rise to the desired intermediate 3, we investigated a radical defunctionalization strategy [8]. To

• envisaged deoxygenation route (Scheme 2), this key transformation saved 2 steps and paved the way for a final reaction sequence that was based on our synthesis of (−)-englerin A (5) [6]. Thus, Wittig olefination of the acetyl group in 3 afforded the sensitive vinyl epoxide 10 along with some cyclized

• ). Retrosynthetic analysis for (−)-oxyphyllol (1) and structures of the guaiane sesquiterpenes (+)-orientalol E (2) and (−)-englerin A (5). Attempted selective deoxygenation of diol 7. a) 1 mol % K2OsO4, NMO, acetone, water, THF, rt, 97%, diastereomeric ratio = 2:1 (ref. [6]); b) PhOC(S)Cl, pyridine, CH2Cl2, 0 °C

Stability of SG1 nitroxide towards unprotected sugar and lithium salts: a preamble to cellulose modification by nitroxide-mediated graft polymerization

• Guillaume Moreira,
• Laurence Charles,
• Mohamed Major,
• Florence Vacandio,
• Yohann Guillaneuf,
• Catherine Lefay and
• Didier Gigmes

Beilstein J. Org. Chem. 2013, 9, 1589–1600, doi:10.3762/bjoc.9.181

• (4.8 g, 12.6 mmol) was added to the previous filtrate (50 mL). After deoxygenation by argon bubbling for 20 min at room temperature, the solution was heated at 80 °C for 3 h. After cooling, EtOAc was added to the media and the product was recovered by precipitation. The obtained white solid was dried

Synthesis of the tetracyclic core of Illicium sesquiterpenes using an organocatalyzed asymmetric Robinson annulation

• Lynnie Trzoss,
• Jing Xu,
• Michelle H. Lacoske and
• Emmanuel A. Theodorakis

Beilstein J. Org. Chem. 2013, 9, 1135–1140, doi:10.3762/bjoc.9.126

• the C-1 center (dr = 9:1) in 81% yield (over three steps) [76]. The stereochemistry of 15 was unambiguously confirmed by single-crystal X-ray analysis of the related tosylate derivative 16 [77]. Deoxygenation of the C-15 primary alcohol was performed by: (a) mesylation of the alcohol with MsCl; and (b

• ) reductive deoxygenation with LiEt3BH (super hydride). The thioketal protecting group was then removed under oxidative conditions with [bis(trifluoroacetoxy)iodo]benzene (PIFA) to yield ketone 10 in good yield (66% over three steps, Scheme 2) [78]. This approach allowed us to produce a sufficient amount of

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

Studies on the substrate specificity of a GDP-mannose pyrophosphorylase from Salmonella enterica

• Lu Zou,
• Ruixiang Blake Zheng and
• Todd L. Lowary

Beilstein J. Org. Chem. 2012, 8, 1219–1226, doi:10.3762/bjoc.8.136

• group at these positions is tolerated very poorly. Conversely, the addition of a methyl group to, or deoxygenation of, O-6 had a much smaller effect, suggesting that this position protrudes from the active site, or is accommodated in a pocket that can tolerate either of these modifications. These

Unprecedented deoxygenation at C-7 of the ansamitocin core during mutasynthetic biotransformations

• Tobias Knobloch,
• Gerald Dräger,
• Wera Collisi,
• Florenz Sasse and
• Andreas Kirschning

Beilstein J. Org. Chem. 2012, 8, 861–869, doi:10.3762/bjoc.8.96

• could not be attributed to the known tailoring transformations. Herein, we now describe for the first time the isolation and characterization of compounds 11f–h sharing, in contrast to all other (pro)ansamitocin derivatives known so far, the common feature of deoxygenation at C-7. In addition

• the keto group at C-9 being in conjugation with the diene system, resulting in a reduced activity of the carbonyl group and an alteration of the macrolactam ring conformation. We based the determination of deoxygenation at C-7 in 13a and 13b on MS data and the appearance of a secondary carbon atom in

• starting compounds 9a and 9b [17]. In order to shed light on the sequence of events leading to deoxygenation, the carbamoylated derivative 12 was again fed to a culture of A. pretiosum HGF073, and the formation of new products was analyzed by UPLC-HRMS of the partially purified crude extract (Scheme 3

Reduction of benzylic alcohols and α-hydroxycarbonyl compounds by hydriodic acid in a biphasic reaction medium

• Michael Dobmeier,
• Josef M. Herrmann,
• Dieter Lenoir and
• Burkhard König

Beilstein J. Org. Chem. 2012, 8, 330–336, doi:10.3762/bjoc.8.36

• (Table 1, entry 12), but some of the material was lost due to ester hydrolysis. Allylic alcohols are completely consumed, but the corresponding alkenes could not be isolated as pure products (Table 2). Mixtures of eliminiation and deoxygenation products, in some cases also rearangement of the

Novel synthesis of pseudopeptides bearing a difluoromethyl group by Ugi reaction and desulfanylation

• Jingjing Wu,
• Hui Li and
• Song Cao

Beilstein J. Org. Chem. 2011, 7, 1070–1074, doi:10.3762/bjoc.7.123

• ) in dry toluene (3 mL). Deoxygenation was continued for 5 min. Azobisisobutyronitrile (AIBN) (0.02 g, 0.1 mmol) was added and the solution was heated at reflux for 9 h (TLC). The mixture was concentrated under reduced pressure and the residue was dissolved in EtOAc (5 mL). The solution was stirred

Bis(oxazolines) based on glycopyranosides – steric, configurational and conformational influences on stereoselectivity

• Tobias Minuth and
• Mike M. K. Boysen

Beilstein J. Org. Chem. 2010, 6, No. 23, doi:10.3762/bjoc.6.23

• -configured ligand scaffold, will bring the 3-O-substituent into a syn-relationship with the oxazoline nitrogen atom and therefore into very close proximity to a coordinated metal centre (Figure 1, I). Deoxygenation of the 3-postion on the other hand will lead to a ligand with comparably little steric

• (amide) 15. For the preparation of 3-deoxygenated ligands, we planned a defunctionalisation of the key intermediate 7. Surprisingly, a thorough search of the literature revealed only one example of the 3-deoxygenation of a glucosamine-derived thioglycoside, reported by Herdewijn et al. in 2006 [31

• ]. Because the Barton–McCombie deoxygenation [32] failed on their N-Troc protected thio aminoglucoside under various conditions, Herdewijn et al. used a sequence via a 3-iodide derivative. To avoid the rather complicated preparation of a 3-iodo derivative, we tried the Barton–McCombie reaction on our

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• consequence of differing on ring sizes, structural manipulation (such as chain branching, deoxygenation, hydroxyl protection, unsaturation), relative position between amine and carboxylic function, and, perhaps most importantly, the spatial arrangement of the amine and acid moieties. The limitations of stereo

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• both this methoxy group and the one at the ring junction. Finally, the nitrogen of the lactam is located in the bridgehead position of a [3.3.0] bicycle resulting in poor delocalization into the adjacent carbonyl. A Barton deoxygenation gave compound 43, which was irradiated to decompose the triazoline

Enantiospecific synthesis of [2.2]paracyclophane- 4-thiol and derivatives

• Gareth J. Rowlands and
• Richard J. Seacome

Beilstein J. Org. Chem. 2009, 5, No. 9, doi:10.3762/bjoc.5.9

• was investigated (Scheme 1). The first step, the reduction of (Sp,RS)-5 to sulfide (Sp)-6, proved the most problematic; use of a large excess of trichlorosilane and triethylamine resulted in deoxygenation in moderate yield after recrystallisation [40]. By comparison, reduction of the less hindered

• by sulfinyl-directed ortho lithiation with n-butyllithium followed by reaction with tosyl azide. The resulting azo[2.2]paracyclophane was reduced in situ to give the amine (Rp,RS)-8 in good yield for the two steps (Scheme 2). Trichlorosilane-mediated deoxygenation proceeded uneventfully to furnished

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

• 82 yielded the butenolide 167. Hydrogenation of the double bond afforded (+)-squamocin K, while diastereoselective dihydroxylation of the same double bond yielded (5S)-hydroxyparviflorin 168. Chemoselective deoxygenation of the C-5 hydroxyl group afforded parviflorin, spectroscopically identical to

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

• David M. Hodgson Leonard H. Winning Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK; Fax: +44(1865) 285002 10.3762/bjoc.4.38 Abstract Tandem deoxygenation–neophyl-type radical rearrangement–electrophile trapping using xanthates

• -azabenzonorbornadienes. Oxidation (using RuO4) and Birch reduction of the 2-aza-5,6-benzonorbornenes provide access to substituted pyrrolidines and tetrahydroindenes, respectively. Keywords: asymmetric synthesis; deoxygenation; radicals; rearrangements; tandem reactions; Introduction Carbon-centred radicals have been

• under conditions [refluxing toluene, thermal initiation by AIBN] similar to those we had previously reported for the tandem deoxygenation–rearrangement–reduction of 7-azabenzonorbornenyl xanthates (e.g. 5 to 8, Scheme 2), although the work in our laboratory had employed a syringe pump in order to

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• 25 was obtained through another cuprate addition, followed by NaBH4 reduction of the ketone and subsequent deoxygenation under Barton-McCombie conditions. Exchange of the MOM for a TBS protecting group and treatment with mCPBA furnished an epoxide, which was converted into allylic alcohol 26 by

Analogues of amphibian alkaloids: total synthesis of (5R,8S,8aS)-(−)-8-methyl- 5-pentyloctahydroindolizine (8-epi-indolizidine 209B) and [(1S,4R,9aS)-(−)-4-pentyloctahydro- 2H-quinolizin- 1-yl]methanol

• Joseph P. Michael,
• Claudia Accone,
• Charles B. de Koning and
• Christiaan W. van der Westhuyzen

Beilstein J. Org. Chem. 2008, 4, No. 5, doi:10.1186/1860-5397-4-5

• alcohol 41 opens up a route to quinolizidine alkaloids containing C-1 methyl substituents (provided, of course, that we can find a better method for deoxygenation, probably by radical-mediated reaction). In addition, alkyl homologues at C-1 should be accessible; one could, for example, replace the alcohol

Part 2. Mechanistic aspects of the reduction of S-alkyl- thionocarbonates in the presence of triethylborane and air

• Florent Allais,
• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 46, doi:10.1186/1860-5397-3-46

• corresponding alkanes with good to excellent yields. Such a process complies with the long-standing pursuit of an environmentally acceptable process for desulfurisation, dehalogenation or deoxygenation that operates under mild reaction conditions. In this context, special attention must be paid to a paper

Part 1. Reduction of S-alkyl- thionocarbonates and related compounds in the presence of trialkylboranes/air

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 45, doi:10.1186/1860-5397-3-45

• -dithiocarbonates (S-xanthates), iodides, O-alkyl-dithiocarbonates (O-xanthates) and related compounds to the corresponding alkanes is very important in organic synthesis, especially in natural products chemistry.[1][2] Deoxygenation (Barton-McCombie reaction) has been largely used to handle sensitive compounds

• deoxygenation of primary O-alkylxanthates under similar conditions is impractical (yield 3%, determined by GC).[14] The comparison of entries 1 and 7 in Table 2 shows that an impressive improvement was obtained in the deoxygenation of O-alkylxanthates by a better understanding of the various steps involved and