Dimethyl-1,5-benzodioxanes

It was the purpose of this investigation to synthesize suitable monomers which could conceivably undergo cyclopolymerization or cyclocopolymerization to lead to large ring-containing polymers. A more specific purpose was to synthesize polymers which would contain ring structures in the polymer backbone which may simulate the properties of the crown ethers (2). Thus a variety of monomers, including l,2-bis(ethenyloxy)benzene, l,2-bis(eth-enyloxy)-4-methylbenzene, 1,2-bis(2-ethenyloxyethoxy)benzene and l,t-butyl-3,4-bis(ethenyloxyethoxy)benzene, as well as model compounds 2,3-dimethyl-1,4-benzodioxane and cis- and trans-2,4-dimethyl -1,5-benzodioxepane, were synthesized and studied. This paper deals with cyclopolymerization studies of the four monomers. 

Dimeth.y1-l,4-benzodioxane [3] [41. Into a stirred solution of 62 g (1.1 mole) K0H, 55 g (0.5 mole) catechol and 1.5 1 DMF in a flask, equipped with mechanical stirrer, pressure-equalizing addition funnel and condenser with drying tube, was added a solution of 2,3-butanediol ditosylate in 500 ml DMF. After stirring at room temperature for 24 hours and refluxing 24 hours, it was mixed with twice the volume of water and extracted with twice the volume of diethyl ether. The extract was dried over anhydrous MgS04 and condensed in a rotary evaporator. Fract. dist. (vac) gave 24 g mixture of cis- [3] and trans-2,3-dimethyl-1,4-benzodioxane [4]. Yield 29.23%. b.p. 96-100°C/6 mm. Anal. Calcd. for C-.H. O, C, 73.12 H, 7.36. Found C, 73.27 H, 7.40. u c c... 

Repeated recrystallization from methanol gave 14 g of trans-2,3-dimethyl-1,4-benzodioxane [4]. m.p. 73-74°C. Column chromatography of the mother liquid, using A12O3 as adsorbent and a 1 1 mixture of petroleum ether and diethyl ether as eluent, and then fractional distillation under vacuum gave 9 g of pure cis-2,3-dimethyl-l,3-benzodioxane [3]. b.p. 96°C/3.5 mm. 

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

Racemic 2,3-butanediol was converted to the racemic ditosy-late, which was then treated with catechol under the influence of NaOH in dimethylformamide (DMF) to yield the desired compounds, cis- and trans-2,3-dimethyl-l,4-benzodioxane [3] and [4]. The solid trans isomer [4] was obtained by repeated recrystallization from methanol. Column chromatography of the mother liquid using AloOj as adsorbent and petroleum ether and diethyl ether in a 1 1 ratio as eluent, gave pure liquid cis isomer [3]. By comparison with the PMR spectra (8) of pure trans- and cis-2,3-dimethyldi-oxane, the solid isomer was identified as trans, and the liquid isomer as cis. The compounds were further characterized by IR, NMR, CMR and elemental analyses. The CMR spectral data for 2 and 4 are summarized in Table I. 

In the second group, 6-hydroxy-2,4-dimethyl-1,3-benzodioxane was synthesised in 72% yield by the addition of hydroquinone during 6-8 hours to a cold acetic acid solution of acetaldehyde containing concentrated hydrochloric acid and reaction at 0-5°C for 3 hours (ref.161), presumably by electrophilic substitution followed by cyclic acetal formation. 

A mixture of 6-nitro-5,8-dimethyl-l,3-benzodioxane and aq. Na-carbonate hydrogenated 2 hrs. at 270°/100 atm. with copper diromium oxide catalyst, whidi is then removed by filtration, the filtrate acidified with coned. HCl, treated with 40%-FeCl3, steam-distilled, and the distillate allowed to react at 40 with Na-dithionite trimethylhydroquinone. Y 78%. H. Otomasu, Chem. Pharm. Bull. 16, 378 (1968). 

Figure 9.9 Synthesis of 2-[2-(2,6-dimetho3q heno3g )ethyI]aminomethyl-l,4-benzodioxane including the information given in the paper to elucidate greenness of the s)mthetie path. THF tetrahydrofuran DMSO dimethyl sulfoxide DCM dichloromethane.

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