Approaches to the Synthesis of Cytochalasans. Part 11. Further transformations and cyclization attempts directed towards proxiphomin

Abstract
Starting from iodoalcohol 9, the monoprotected dialdehyde 5 was synthesized (Scheme 2) and converted to 17 by reaction with oxo‐phosphonate 15 (Scheme 3). The latter was prepared from 13. Cyclisation of 17 to the target compound 18 failed. Also the attachment of thiol 22 to lactone 19 was unsatisfactory (Scheme 4). Therefore, the building blocks 28 and 29 were synthesized using diene 33 and diester 30 as starting material for 28 and 9 for 29 (Scheme 5 and 6). Hydroxy acid 28 was converted into formyl‐ester 46 (Scheme 7). However, the condensation of its derivatives 48 and 49 with ‘Umpolung’ of the carbonyl reactivity was unsuccessful, probably due to steric hindrance.