Enantioselective Synthesis of Linear Polypropionate Arrays

Significance

Reaction of anthracene-tagged organosilane (R)-1 with benzaldehyde in the presence of triflic acid and methoxytrimethylsilane afforded syn-homoallylic ether 2 (step I). Without further purification, crude 2 was sequestered to polystyrene maleimide resin 3 (loading: 1.54 mmol/g) by microwave-assisted [4+2] cycloaddition (step II) to give resin 4. Subsequent ozonolysis of the olefin took place to release a mixture of dimethyl acetal and aldehyde, which was readily converted into dimethyl acetal 5 (65% yield, > 95% purity, four steps, dr > 30:1) using montmorillonite K10 clay/CH(OMe)₃ (step III). Compound 5 was subjected to the next series of steps I-III with (R)-1 to give dimethyl acetal 6a (64% yield, dr > 20:1). Stereoisomer 6b was also obtained by analogous procedures (steps I-III) from (S)-1 (78% yield, dr > 9:1).