6.8- Dioxabicyclo octane, preparation

Polymerization of 6,8-dioxabicyclo[3.2.1]octane, 2, has been most extensively studied among bicyclic acetals. This monomer is readily prepared from 3,4-dihydro-2H-pyran-2-carbaldehyde 1 by reduction with sodium borohydride followed by add-... 

As a first step in the prepartion of polymers patterned after the repeating unit of nonactin 56, Moore and Kelley53 synthesized 3,8-dioxabicyclo[3.2.1 ]octan-2-one 57 and its corresponding polyester 58. The monomer was prepared from 5-hydroxy-methylpyran-2-carboxylic acid in overall yield of 20%. It was heated with a catalytic amount of tert-butoxytitanate under nitrogen for 3 hr at 100 °C. The temperature... 

Two formal syntheses of (-)- [80] and (+)-kumausallene [81] followed this route and relied on the enantioselective preparation of the 2,6-dioxabicyclo[3.3.0]octane core 69 starting from diethyl tartrate or an appropriate chiral sulfoxide. In contrast, Evans et al. [82] used a distinct biomimetic approach in their enantioselective synthesis of the natural product (-)-62 (Scheme 18.23). 

Vogel185 used 3-aza-6,8-dioxabicyclo[3.2.1]octane based chiral dienophiles to prepare anthracyclines and anthracycline derivatives. 

Preparation of 2,7,8-trioxabicyclo[3.2.1]octanes by the oxidation of 2,7-dioxabicyclo[2.2.1]heptanes with m-chloroperbenzoic acid [189]. 

Compared with 49, 2,5-dioxabicyclo[2.2.2]octan-3-one (54) prepared from sodium 3,4-dihydro-2//-pyran-2-carboxylate has a much low polymerization reactivity [54] Lewis acids such as antimony pentachloride, phosphorus pentafluoride, and boron trifluoride etherate were not effective at all to initiate the polymerization of 54. Trifluoromethanesulfonic acid induced the polymerization of 54, but the yield and molecular weight of the polymer were low. Bicyclic lactone 54 was allowed to polymerize with anionic and coordination initiators such as butyl-lithium, lithiumbenzophenone ketyl, and tetraisopropyl titanate. However, the... 

On the other hand, cationic lactone polymerization may be also used to prepare cyclic oligomers of specific ring size with reasonable yield. Polymerization of bicyclic lactone, 6,8-dioxabicyclo[3.2.1]octan-7-one, generates a repeating unit containing ester and ether bonds ... 

Dioxabicyclo[3.2.1]octane, the carbon skeleton of 1,6-anhydropyranose, is present in plant extracts and pheromones, and it is a crucial fragment in orally active 5-lipoxygenase inhibitors. The synthon 6,8-dioxabicyclo[3.2.1]octane-3-one (1102) is readily prepared from ( S)-malic acid-derived diol 45a, as shown in Scheme 162 [234]. Silylation of ketone 1099 with TBS triflate provides the kinetically derived silyl enol ether 1100 (10 1 kinetic vs. thermodynamic selectivity) in high yield. Lewis acid cyclization of the cyclic ortho ester 1100 affords the bicycloketone 1102 in 25.5% overall yield starting from (iS)-malic acid. 

A particularly attractive feature of the methodology described above is the ability it confers to prepare a variety of 5-alkyl-6,8-dioxabicyclo[3.2.1]octanes useful in natural product... 

Koo et al. have developed an efficient method for the preparation of diverse co-formyl-a,p-unsaturated carbonyl compounds 268 and 273 that relied on the Pb(OAc)4-promoted oxidative ring cleavage of cyclic 1,2-diols 267 and 272, respectively, which in turn can be readily obtained by the 1,2-addition of various nucleophiles to a cx -acetoxy-substituted conjugated cycloalkenones 266 and a-acetoxy cyclohexanone 271. The authors also optimized the conditions for the intramolecular MBH reactions of 268 and 273. The utility of this sequence is demonstrated by the syntheses of chromones 270 and the precursor (274) of the compound containing the 6,8-dioxabicyclo[3.2.1]octane ring (Scheme 1.98). ... 

The key of the synthesis was preparation of the 5,e-dihydroxy ketone intermediate, precursor of the 6,8-dioxabicyclo[3.2.1]octane skeleton. The serinol fragment (S)-15 was prepared from the known D-serinol derivative (S)-13 [8] in a series of straightforward steps. The hydroxyl group was first propargy-... 

Preparation of Racemic 6,8-Dioxabicyclo[3.2.1]octan-7-one. To an aqueous solution of sodium 3,4-dihydro-2H-pyran -2-carboxylate (50 g) was added 6N hydrochloric acid (64 ml) in a few minutes keeping the temperature below lO C with external ice-cooling. After the addition of a sufficient amount of sodium chloride to saturate the solution, it was extracted several times with diethyl ether. The ether extract was washed three times with a saturated sodium chloride aqueous solution and dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure and the residue was distilled. Yield 78% bp 68-70 C (4 mmHg) (lit.[9], bp 62-64 C (3 mmHg)). The monomer was dried over calcium hydride and fractionally distilled just before use. 

Preparation of (+)-(1R,5R)-6,8-Dioxabicyclo[3.2.1]-octan-7-one. An aqueous solution of sodium 3,4-dihydro-2H-pyran-2-carboxylate (25 g) was slightly acidified with 6N-hydrochloric acid, and the liberated carboxylic acid was extracted several times with diethyl ether. The ether extract was then added to an ice-cooled diethyl ether solution of dehydroabietylamine (46 g) which had been purified by repeated recrystallization of its acetate. Immediately after the addition, a white mass was formed. After being allowed to stand for half an hour, it was separated and re-... 

Sumitomo and coworkers prepared 6,8-dioxabicyclo[3.2.l]octan-7-one (37) and 6-aza-8-oxabicyclo[3.2.lJoctan-7-one (36) from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer), and polymerized these monomers by ring-opening methods (Fig. 15). The lactam (36) was polymerized to a high molecular weight polyamide (39). 

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