A new method for preparing optically active 1,3-dioxin-4-one derivatives is presented. A series of prochiral 2,2-bis(hydroxymethyl)-1,3-dioxin-4-ones was synthesized by [4+2]cycloaddition of acylketene to protected 1,3-dihydroxy-2-propanone derivatives followed by deprotection of the hydroxyl groups. Desymmetrization of the prochiral dioxinones by lipase-catalyzed monoacetylation afforded optically active 2-(hydroxymethyl)dioxinones. Intramolecular photo[2+2]cycloaddition of ω-alkenyl esters of these alcohols provided an efficient method for regio-, diastereo-, and enantioselective synthesis of cyclobutanols.Graphic(R)-[2-(Hydroxymethyl)-6-methyl-4-oxo-4H-1,3-dioxin-2-yl]methyl acetateC9H12O6E.e.=98%[α]D26=+20.2 (c 1.14, CHCl3)Source of chirality: lipase catalystAbsolute configuration: R(S)-[2-(Hydroxymethyl)-4-oxo-4H-1,3-dioxin-2-yl]methyl acetateC8H10O6E.e.=98%[α]D26=+15.5 (c 1.07, CHCl3)Source of chirality: lipase catalystAbsolute configuration: S(R)-[2-(Hydroxymethyl)-4-oxo-6-phenyl-4H-1,3-dioxin-2-yl]methyl acetateC14H14O6E.e.=98%[α]D26=+51.9 (c 1.07, CHCl3)Source of chirality: lipase catalystAbsolute configuration: R