Seebach-Corey umpolung framework: a1 (natural electrophile) ↔ d1 (dithiane nucleophile) polarity flip

Seebach-Corey 1979 umpolung classification: the natural polarity of an sp²-carbonyl is a1 (acceptor at C, donor at O); dithiane protection (1,3-dithiane) swaps the carbonyl carbon's role from electrophile to nucleophile (d1), enabling…