Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• ] which could be separated by chromatography on silica gel. Hydroboration and lactonization of 12 furnished a mixture of the C4-epimers a and b that once again needed to be separated by chromatography on silica gel [23]. Analytical data of the first eluting component a were in accordance with those

• intermediate, the stereoselective synthesis of all eight stereoisomers could be achieved (Figure 5). The aldehyde 15 could be readily prepared from commercially available pure and cheap (R)-limonene (14) [25][26][27]. Non-selective hydroboration of the double bond in the side chain of 15 would yield a pair of

• upon intramolecular aldol condensation [25][26][27]. Subsequently, the aldehyde 15 was reduced to the allylic alcohol 19 with LiAlH4 and converted into the acetate 20 [28]. Hydroboration of 20 using disiamylborane proceeded with high stereoselectivity affording 16 as a single stereoisomer [17][28

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

• -dihydro-2H-1,2-oxazines. Their enol ether double bond was then subjected to a hydroboration followed by an oxidative work-up, and finally the auxiliary was removed. The described three-step procedure enabled the synthesis of enantiopure hydroxylated 1,2-oxazines. Typical examples were treated with

• reagents [33]. Here we report on the application of a nitrone with an L-erythronolactone-derived auxiliary for the synthesis of 3,6-dihydro-2H-1,2-oxazine derivatives of type D. Their selected transformations, including hydroboration of the enol ether moiety, oxidative work-up, glycosyl cleavage, and

• ], 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

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

Convenient methods for preparing π-conjugated linkers as building blocks for modular chemistry

• Jiří Kulhánek,
• Filip Bureš and
• Miroslav Ludwig

Beilstein J. Org. Chem. 2009, 5, No. 11, doi:10.3762/bjoc.5.11

• (Figure 1, Table 1). Results and Discussion Synthesis of boronic pinacol esters 3–6 Whilst two styryl dioxaborolanes 3a–b are known [31][32] and commercially available, the N,N-dimethylamino substituted derivative 3c needed to be synthesized. In order to achieve pure (E)-3c, at first, a hydroboration of

• the commercially available terminal acetylene 2c with catecholborane was examined. Despite all attempts to optimize the reaction conditions, 3c could not be prepared this way and was not even detected in the crude reaction mixture. Thus the above hydroboration reported by Perner and co-workers [33

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions

• Rajeev K. Shrivastava,
• Elise Maudru,
• Gurdial Singh,
• Richard H. Wightman and
• Keith M. Morgan

Beilstein J. Org. Chem. 2008, 4, No. 43, doi:10.3762/bjoc.4.43

• , (Scheme 7), could be successfully removed on treatment using these conditions. Hydroboration of cyclohexene 14 obtained from cyclisation of 9a, following oxidative workup gave the cyclohexanol 54 in 77% yield. Removal of the isopropylidene and MOM protecting groups afforded a fully deprotected carba-β-D

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

• from 7-azabenzonorbornadienes gives 3-exo-substituted 2-aza-5,6-benzonorbornenes, which in some cases undergo isomerisation to (aminomethyl)indenes. The starting xanthates are accessible in good yields and high enantiomeric ratios via asymmetric hydroboration of (aryne/pyrrole-derived) 7

• -rearrangement-trapping of 2-azabenzonorbornenyl xanthates established, we next sought to achieve an asymmetric access to such systems by asymmetric hydroboration. Previous test reactions had indicated that efficient metal-catalysed asymmetric hydroboration [27] was difficult to achieve in this system [28] and

• therefore stoichiometric hydroboration was examined. The timely work of Laschat and co-workers in an analogous tropinone system [29] suggested the application of diisopinocampheylborane (Ipc2BH) [30][31], which with cycloadduct 14 at 0 °C gave alcohol 15 in 84% yield (68% at −10 °C, Scheme 3). HPLC analysis