8-Oxabicyclo octane ring system

A novel intramolecular alkylation using a spiroketal (14) with BFj.OEt, in THF at reflux forms the benzene-fused 8-oxabicyclo[3.2.1]octane ring system (15) in satisfactory yield. IV-Tosylpipecolinic acid (16) in the presence of sulfuric acid in benzene forms the unexpected aromatized derivative (17) in 18% yield and the mechanism is suggested to involve the reaction of intermediate (18) with benzene to form (19). Cumyl and r-butyl hydroperoxides have been used for the electrophilic alkylation of activated aromatic substrates, mainly phenols and phenol ethers.The hydroperoxides behave differently as far as catalysis and regioselectivity are concerned. The latter is believed to be explicable by steric and reactivity/selectivity considerations. Electrophilic r-butylation may be followed by radical reactions due to the r-butyl... 

The synthesis of the oxabicyclo[3.2.1]octan-2-one ring system was successfully accompUshed via the 1,3-dipolar cycloaddition of 6-membered ring carbonyl yUdes. hi a reactivity profile similar to that of the five-membered carbonyl yhdes (see Schemes 14,15), the carbonyl ylide derived from 1-diazo-... 

The oxabicyclo[3.2.1]octan-2-one ring systems form a core skeleton of many naturally existing molecules. In an approach towards guaianolide sesquiterpenes, their hydroazulenic framework has been constructed through a rhodium(II)-catalyzed reaction [82] of the a-diazo ketone 106 with DMAD to afford the oxatricyclic system 107, which forms the skeleton of ambrosic acid 108 (Scheme 33). 

Malonate-substituted cyclopropanes are often considered as synthetic building blocks due to the specific reactivity of their carbocyclic ring systems. For instance, total synthesis of ( )-bruguierol A was achieved in several steps that involved cyclopropanation of 2-(2-ally 1-4-methoxyphenyl)-2-methyl-1,3-dioxolane with dimethyl diazomalonate and [Rh2(esp)2] as catalyst (eq 44). The characteristic 2,3-benzofused 8-oxabicyclo-[3.2.1]octane core of bruguierol was constructed via a Sc(OTf)3-catalyzed intramolecular [3+2] cycloaddition of the cor-... 

A very intriguing system 31 with donor-acceptor substitution pattern can be obtained by an intramolecular cyclopropanation 22). The tricyclic product 31 permits several ring cleavage reactions (Scheme 3), some of which are not known for less strained cyclopropanes. All methods lead to oxabicyclo[2.2.2]octane derivatives. Thus, hydro-genolysis proceeds under relatively mild conditions breaking the bond between the donor and the acceptor substituted carbons exclusively. 

Bridged ethers incorporating stereocontrolled placement of functionality can be prepared by SnCU-induced cyclization of 3,4-epoxy alcohols. A reaction sequence with a ring contraction and tandem cyclization enables the construction, from unfunctionalized alkenes or arenes, of the 8-oxabicyclo[3.2.1]octane system with one or two additional fused rings (Eq. 51) [84]. 

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