9-Oxabicyclo nonane synthesis

Fig. 11 Synthesis of (+)-(lfi,6S)-cw-8-oxabicyclo[4.3.0]nonan-7-one from cw-l,2-bis(hydroxy-methyl)cyclohexane catalyzed by HLADH. The cofactor NAD+ is regenerated by the system pyruvate/L-LDH...

The tandem cyclization/intermolecular cycloaddition procedure is also feasible for the synthesis of 9-oxabicyclo[4.2.1]nonane derivatives via the generation of seven-membered cyclic carbonyl ylides. The Rh2(OAc)4-catalyzed decomposition of 719 in the presence of DMAD or methyl propio-late in benzene gives 720 together with the product of a formal carbenoid... 

The excision of the keto bridge present in tricyclo[5.3.1.1 ]dodecan-l 1-one taken from the work of Cha et al. on synthetic studies of taxol deserves special mention. Highly functionalized derivatives of bicyclo]5.3.1]undecane are obtained using the DIB/I2 system (Eq. 11) [38]. The fragmentation of a related derivative of oxabicyclo[3.3.1]nonan-9-one is used by the same authors as a key step in the synthesis of cK-2,8-disubstituted oxocanes (Eq. 12) [39]. 

The synthesis of the twistane-ketal 279 using endo-6-hydroxy-9-oxabicyclo[3.3.1]-nonan-2-one (274) or its acetate 227, resp., was nevertheless successful by applying the following route according to a procedure by Inhoffen etal. the keto-acetate 221 was treated with trimethyl orthoformate. From the reaction mixture which contained the dimethoxy-ketals 222 and 223 as well as the enolethers 224 and 225, the acetates 222 (63%) and 224 (5%) were isolated by chromatography. On base-hydrolysis they gave the alcohols 223 and 225. Pyrolysis of the ketal 222 and simultaneous distillation yielded 67% of the enolether 224. Finally by treating the dime-... 

The subsequently applied synthetic scheme was analogous to the one for the corresponding racemic compounds (see 2.2.2.I., 3.2.3. and 3.2.4.). Treatment of the (—)-alcohol 379 with iodine in chloroform yielded the (-)-10° -iodide 383 as sole product. Its reaction with silver tosylate in acetonitrile led to a mixture of 10°(7).tosyloxy-isotwistane 384 and -twistane 386, which was directly treated with LiAlH4 in refluxing dioxane to give a mixture, easily separable by vpc., of (—)-2,7-dioxa-isotwistane 385 [oc]d = —23.3 0.7°) and (-)-2,7-dioxa-twistane 387, see Table 8). The absolute configuration of 387 [(—)-( R, 3R, 6R, 8R), right-handed helix (P)] and of all other compounds involved in its synthesis was determined by chemical correlation with (—)-(2S)-malic acid (559). As relais compounds served the endo-2-hydroxy-9-oxabicyclo[3.3.1]nonanes +)-390 and (—)-J97, (-t)-5-hydroxy-cyclooct-l-ene [ +)-392] and the 4-methoxy-suberic acid dimethylester —) 393 and +)-394. 

The synthesis of oxonium ylides by catalytic reactions of diazocarbonyl compounds with ethers has numerous applications in the preparation of natural products [127]. Two diastereomers of oxabicyclo[4.2.1]-nonane were obtained from ylide intermediates, which were produced from the... 

The use of Cr(0)-promoted 6 r - - 2 r-cycloaddition in the synthesis of pharmacologically active natural products has been reviewed. The 6 -I- 3-cycloaddition of dimethylaminofulvene (194) with benzoquinones provides an efficient route to the 3-oxabicyclo[4.3.0]nonane system (195) (Scheme 76). Density-functional theory calculations provide evidence for a feasible concerted antara-antara cycloaddition for the 6-I-4-reaction of c -hexa-l,3,5-triene with buta-1,3-diene. Azulene-1,5-quinones (196) and azulene-l,7-quinones undergo a variety of 6-1-4- and 2-1-4-cycloaddition reactions with cyclic dienes and cycloheptatrienes to produce cycloadducts, e.g. (197) and (198) (Scheme 77) ... 

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