Weso-dialdehyde

The Hajos-Parrish-Eder-Sauer-Wiechert synthesis (Scheme 5) was the first example of an intramolecular proline-catalyzed asymmetric aldol reaction. Systematically, this reaction can be described as a 6-enolendo cyclization. In 2003, List et al. described the first example of an intramolecular enolexo aldolization 85). This approach was then used by Pearson and Mans for the synthesis of (-i-)-cocaine 92, starting from the weso-dialdehyde 90 on treatment with (S)-12 86). This desymmetrization process gave 91 as a mixture of epimers with good enantio-selectivity. The tropane skeleton 91 could be further transformed into +)-92 by conventional means (Scheme 21). 

Vares and Rein have developed a powerful approach to tetrahydrofurans where they coupled an asymmetric Homer-Wadsworth-Emmons (HWE) reaction with a Pd-catalyzed ring closure to generate cis- and tran -tetrahydrofuran derivatives (Schemes 76 and 77) [82]. From weso-dialdehyde 289, asymmetric HWE gave E-alkene isomer 291 with high levels of diastereoselectivity. Aldehyde reduction was followed by pivaloyl migration to afford cyclization precursor 292 in 63 % yield. Pd-catalyzed ir-allyl formation and cyclization proceeded with overall retention of stereochemistry to give 2,5-cis-tetrahydrofuran 293 in 76 % yield. 

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See also in sourсe #XX -- [ ]

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