1.4- Dioxene

Similar dehydrofluorination occurs with polyfluorinated heterocycles. 2,2-Bis(trifluoromethyl)-3,4-difluorooxetane gives 3-fluoro-4,4-bis(trifluoromethyl)-2-oxete [19] (equation 17), and heptafluoro-p-dioxane yields hexafluoro-p dioxene [20] (equation 18)... 

Dioxenes react, as expected, to produce thermally unstable dihalocyclo-propanes in high yield [51, 89]. Upon heating, the bicyclic system rearranges to yield the dichloromethyl-1,4-dioxene, whereas the tricyclic system, derived from the benzo-l,4-dioxene undergoes ring expansion to produce the benzo-1,5-dioxepin (Scheme 7.11). 

Triraethyl-l,3-dioxen-4-one is comtnerical 1y available from the Aldrich Chemical Company, Inc. and may be used without further purification. 

Diethylphosphonomethyl-2,2-dimethyl-1,3-dioxen-4-one Phosphonic acid, [(2,2-dimethyl-4-oxo-4H-l, 3-dioxin-5-yl)methyl] -, diethyl ester (11) (81956-28-7)... 

In a thorough study on photooxidation of 2,5-dimethyl-2,4-hexadiene (455) it was found that 1,2-dioxene 456, 1,2-dioxetane 457, hydroperoxy dienes 458 and 459 and, when methanol was used as solvent, also hydroperoxy(methoxy)octene 460 are formed (Scheme 124) . Product distribution was found to be highly solvent dependent. These results led investigators to postulate a mechanism involving the intermediacy of perepoxide 461 and zwitterion 462 (Scheme 124). Accordingly, the product of [4-1-21-cycloaddition 456, the product of [2 + 2]-cycloaddition 457, as well as the products 458 and 459 deriving from ene-addition would originate from polar intermediates 461 and... 

Most partially saturated ring systems, 2,3-dihydro-l,4-dioxin 10 (sometimes named as 1,4-dioxene), 2,3-dihydro-1,4-dithiin 11, 2,3-dihydro-l,4-oxathiin 12, 2,3-dihydro-l,4-benzodioxin or 1,4-benzodioxane 13, 2,3-dihydro-l,4-benzodithiin 14, and 2,3-dihydro-l,4-benzoxathiin 15 are well investigated. Ring numbering for compounds 10-12 is followed as shown, independently of the presence of substituents. 

The potential energy barrier of 1,4-benzodioxan 13 to ring inversion is 1-2 kcal moP lower than that of 1,4-dioxene 10, typically 6.9 and 8.7 kcalmoP (HF/6-31G ) and 7.5 and 8.8kcalmoP (B3LYP/6-31G ), respectively <1998MI173>. 

A Claisen rearrangement of the 1,4-dioxene 69 provided the pyran 70 asymmetrically (Equation 10) <1998JA12702>. 

Palladium-catalyzed reactions are the most studied. Eor example, 5-tributylstannyl-l,4-dioxene 130 underwent a cross-coupling reaction with the enol ttiflate 131 in refluxing THF in the presence of LiCl and a catalytic amount of Pd(PPh3)4 (Equation 19) <1996TL7013>. 

Synthesis of 2,3-dihydro-l,4-dithiin 11 was accomplished from l,3-dithiol-2-one 247 in the presence of dibro-moethane and potassium hydroxide <1998JOG3952>, while reaction of 2,3-dichloro-l,4-dioxane with powdered Zn in hexamethylphosphoramide (HMPA) was used for the synthesis of 1,4-dioxene 10 <1998JPP10067773>. To obtain substituted 1,4-oxathianes, the hydrogenation of the corresponding partially saturated compounds has been employed <2001J(P1)2604>. 

Cycloaddition reactions occur between singlet oxygen and cisoid 1,3-diene systems yielding cyclic peroxides with the skeleton of 1,2-dioxenes according to the following scheme ... 

Treatment of 23-disubstituted 1,4-dioxenes with a catalytic amount of camphotsulfonic acid in dichloiomethane at room temperature afforded substituted furans <99TL2S21>. 

A 100-ml autoclave was charged with ethyl acetate (24 parts), 1,4-dioxene (20 parts), and t-bu ty 1 pcrox pi val ate (0.3 parts) and then treated with chlorotrifluoroethylene (31 parts) and polymerized at 55°C for 13 hours. The precipitated polymer was isolated and dissolved in 150 ml of tetrahydrofuran (THF) and then precipitated in methanol, the process being repeated twice. Thirty-five grams of product were isolated having a Tg of 154°C and an Mn of28,000 Da with a refractive index of 1.459. The material was soluble in most organic solvents and formed transparent films. 

Dioxene derivatives used in the step 1 copolymerization process. 

Copolymers containing 1,4-dioxene derivatives are illustrated below. 

---