Alkylation of planar chiral cationic pi-allylmolybdenum complexes - the total synthesis of cryptophycin 4

[摘要] We have investigated the alkylation of planar chiral cationic pi-allylmolybdenum complexes 2.1 and 2.2 with a variety of functionalised alpha-alkoxyalkylcopper(I) nucleophiles. Complexes 2.1 and 2.2 are readily formed from the corresponding homochiral allylic acetates (S)- and (R)-2.12 and a suitable Mo(0) source with retention of facial stereochemistry (Scheme 1). Excellent selectivity for attack anti to the metal fragment yields products of overall inversion of configuration, 2.3 and 2.4. Good regiocontrol (typically > 8:1) results from steric discrimination between the termini of the allyl unit. The selectivity is obtained without the need to control central chirality at the metal, in contrast to literature precedent. [diagram] We have applied the methodology to natural product synthesis. Cryptophycin 4 (4.110) was prepared via the coupling of novel cationic complex 4.1 and homochiral nucleophile 4.2 as synthetic equivalents for synthons 4.5 and 4.7 respectively (Scheme 2). [diagram].

[发布机构] University:University of Glasgow

[关键词] Pharmacology