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