52717-73-4Relevant articles and documents
Total synthesis of (±)-α-isosparteine, (±)-β- isosparteine, and (±)-sparteine from a common tetraoxobispidine intermediate
Norcross, Neil R.,Melbardis, John P.,Solera, Margarita Ferris,Sephton, Mark A.,Kilner, Colin,Zakharov, Lev N.,Astles, Peter C.,Warriner, Stuart L.,Blakemore, Paul R.
, p. 7939 - 7951 (2008/12/23)
(Chemical Equation Presented) The three title alkaloids were separately prepared in stereocontrolled fashion from a common tetraoxobispidine precursor, 3,7-diallyl-2,4,6,8-tetraoxo-3,7-diazabicyclo[3.3.1]nonane (16). Bisimide 16 was generated from malonate via acid promoted cyclization of the Knoevenagel condensation adduct 1,1,3,3-propanetetracarboxamide. (±)-α- Isosparteine (dl-2) was elaborated from 16 in 28% overall yield by a two-directional synthetic sequence composed of four reactions: double addition of allylmagnesium bromide, ring-closing olefin metathesis (RCM), hydrogenation, and borane mediated reduction. (±)-β-Isosparteine (dl-3) was targeted along similar lines by a strategic reversal in allylation and reduction operations on the core synthon. Thus, 16 was advanced to dl-3 in five steps and 12% overall yield by a reaction sequence commencing with sodium borohydride mediated reduction and followed by double Sakurai-type allylation of the resulting bishemiaminal. The synthesis of dl-3 was concluded by RCM and then global reduction (H2, Pd/C; LiAlH4). The final target, (±)-sparteine (dl-1), was secured in six steps and 11% overall yield from 16 by monoreduction and Sakurai allylation, followed by allyl Grignard addition and then RCM and global reduction as before. Reasons for the inherent C 2-type regioselectivity of net double nucleophilic additions to tetraoxobispidines are discussed and enantioselective oxazaborolidine mediated reduction of the N,N′-dibenzyl congener of 16 is reported.
