[290-13-1] · C4H6O2 · 4H-1,3-Dioxin · (MW 86.10)
Physical Data: bp 97-99 °C.
Solubility: sol THF, ether, hexanes.
Preparative Methods: by elimination of 5-tosyloxy-1,3-dioxane in DMSO using Potassium t-Butoxide5 or KOCMe2C6H136 as the base. A more convenient procedure employs triethylene glycol as the solvent and Potassium Hydroxide as the base.2
Handling, Storage, and Precautions: thermally labile. A rapid distillation is required in order to prevent decomposition via retrocycloaddition to acrolein and formaldehyde.
4H-1,3-Dioxin undergoes rapid metalation upon treatment with s-Butyllithium or t-Butyllithium to provide the allylic anion (1).1 A variety of electrophiles such as alkyl halides, epoxides, aldehydes, and ketones can be employed in subsequent alkylation reactions to afford 4-substituted dioxins which smoothly undergo bis-hetero retrocycloaddition reactions upon refluxing in toluene (4-12 h) to provide (E)-a,b-unsaturated aldehydes, presumably through a boat-like transition state with the alkyl substituent in a pseudoequatorial position (eq 1).1 Moreover, the thermal generation of b-substituted acroleins has been exploited in a one-pot retrocycloaddition-cycloaddition sequence (eq 2).1
Numerous b-formylvinyl anion equivalents have been previously reported. However, the use of all of these equivalents requires at least one reagent-mediated step to unravel the a,b-unsaturated aldehyde after the alkylation step, e.g.: (2) HgCl2, MeCN, H2O, 50 °C;7 (3) H2O2;8 (4) H3O+;9 (5) H3O+;10 (6) 1 H3O+, 2 NEt3;11 and (7) 1 Pt, e-, 2 NEt3.12
4-Alkyl-1,3-dioxins, such as the one shown in eq 1, can be further metalated and alkylated with excellent regioselectivity to provide 4,6-dialkyl-1,3-dioxins (eq 3). Hydroboration reactions of 4,6-dialkyl-1,3-dioxins proceed with complete stereoselectivity from the face opposite the 6-alkyl substituent to provide, after oxidative workup, a single 5-hydroxy-substituted dioxin which can be hydrolyzed to an anti,anti-1,2,3-triol (eq 4). Excellent diastereofacial discrimination is similarly observed in the hydrogenation reactions of 4,6-dialkyl-1,3-dioxins to provide only a syn-1,3-diol after hydrolysis (eq 5).
4H-1,3-Dioxin participates in Heck reactions with a variety of aryl halides and aryl triflates to afford 4-aryl-substituted dioxins which, upon thermolysis in refluxing toluene, are transformed to 3-arylacroleins (eq 6).3
Raymond L. Funk
Pennsylvania State University, University Park, PA, USA