2-Oxabicyclo 5.4.0 undecan

In several natural product syntheses, it has been demonstrated that a tandem ylide formation/rearrangement sequence provides a convenient method to construct synthetic key intermediates containing a oxabicyclo[5.3.1]undecane ring system (e.g., neoliacinic acid and labiatin). This transformation also served to prepare the oxabicyclo[6.2.1]undecane system of ( )-vigulariol (Scheme 79) <2007AGE437>. 

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]. 

Benzoyl 4a-decalyl peroxide (m.p. 67-68° 0.28 g) was boiled for 1 min with pyridine hydrochloride (0.2 g) in pyridine (2 ml). After cooling, the mixture was poured into dilute sulfuric acid, and the precipitated oil was placed in a refrigerator for crystallization. This afforded ll-oxabicyclo[4.4.1]undecan-l-yl benzoate (0.15 g) which after recrystallization from aqueous methanol had m.p. 96-97°. 

In 1989 McDougal and co-workers presented an access to some racemic models of the 1 l-oxabicyclo-[6.2.1]undecane framework found in furanoheliangolides (the C/D ring system) [30]. The key reaction of their approach involved the ozonolysis of a functionalized oxa-bridged octalin 27, which provided the desired 1 l-oxabicyclo[6.2.1]undecane framework 28 (Scheme 3). Their synthetic approach started from the Diels-Alder reaction of 2-methyl-3-phenylthiofuran 23 with maleic anhydride. Namely, siteselective a-lithiation of vinyl sulfide 22, prepared from the conjugate addition product of thiophenol and acrolein, then quenching the... 

Scheme 16.29 Route to oxabicyclo[6.2.1]undecane litoph5niin skeleton by Clark and Wong.

The keto-epoxide (273) can be cyclized with formic acid or KOBu -BuOH to give derivatives of bicyclo[4,4,0]decan-2-on-7-ol, but with aluminium trichloride or basic alumina gives the products (273a) and (273b), and related products with the ll-oxabicyclo[5,3,l]undecane skeleton. ... 

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