Enantioselective synthesis of chromans for the preparation of enantiopure vitamin E and analogues

Article abstract of DOI:10.1055/s-1997-1278

Coupling of the differently protected (hydroxymethyl)enynes 11 a-e and 12a-c with the iodoarene 7 in the presence of catalytic amounts of Pd(PPh₃)₄ afforded the arylenynes 5a-e and 6a-c which were transformed into the monoprotected chiral trihydroxy compounds 13 a-d and 14a,b by Sharpless bishydroxylation with >95% ee for 13 a-d, 91% ee for 14b, and 64% ee for 14a. A 5-step transformation of 13a led to the desired chroman derivative 3a which was cleaved to give the aldehyde 2 a known precursor for the enantioselective synthesis of vitamin E.