Epoxides intramolecular epoxide ring-opening

Although the enantioselective intermolecular addition of aliphatic alcohols to meso-epoxides with (salen)metal systems has not been reported, intramolecular asymmetric ring-opening of meso-epoxy alcohols has been demonstrated. By use of monomeric cobalt acetate catalyst 8, several complex cyclic and bicydic products can be accessed in highly enantioenriched form from the readily available meso-epoxy alcohols (Scheme 7.17) [32]. 

An alternative disconnection of homopropargylic alcohols substrates for intramolecular hydrosilylation is the opening of an epoxide with an alkynyl anion. This strategy was employed in a total synthesis of the macrolide RK-397 (Scheme 20). Epoxide ring opening serves to establish homopropargylic alcohol C with the appropriate stereochemistry. A hydrosilylation/oxidation protocol affords the diol E after liberation of the terminal alkyne. The... 

The key bond closure in Scheme 13.21 is somewhat similar to that used in Scheme 13.20 but is performed on a bicyclo[4.4.0]decane ring system. The ring juncture must be cis to permit the intramolecular epoxide ring opening. The required cis ring fusion is established during the catalytic hydrogenation in step A. 

However, these have not been the only approaches to the synthesis of these ring systems. For example, Sasaki et al. were able to use an intramolecular nucleophilic ring opening of an epoxide with sodium dimsylate to form the oxepane ring as illustrated in the conversion of 34 to 35 <99JOC9399>. 

Narjes, F. Bolte, O. Icheln, D. Konig, W. A. Schaumann, E. Synthesis of vinylcydopro-panes by intramolecular epoxide ring opening. Application for an enantioselective synthesis of dictyopterene A. /. Org. Chem. 1993, 58, 626-632. 

Other synthetically useful intramolecular epoxide ring openings have been reported. For example, the strained methylene epoxide 79, derived from DMD epoxidation of the corresponding allene 78, undergoes spontaneous isomerization to the lactone 81 via attack of the... 

Some noteworthy intramolecular nucleophilic ring openings have been reported in the recent literature, which can be used to prepare functionalized heterocycles of synthetic interest. For example, the highly oxygenated epoxide 100 undergoes rearrangement induced by boron trifluoride etherate, whereby anchimeric assistance from the pendant phenylthio substituent leads to an intermediate episulfonium ion 101 which subsequently suffers 5-e o-tet cyclization to form the tetrahydrofiiran derivative 102 <03TL5547>. 

Feldman has reported two interesting exeunples of epoxide ring opening. The opening reaction in the epoxides (34a) and (34b) affords an ylide-like species that is intramolecularly trapped to yield the two adducts (35a) and (35b). The 3-substituted derivative (34b) also affords another product identified as (36). The formation of this product is thought to involve a Norrish Type I process proceeding via (37) to the lactone (38) which then undergoes [2-1-2] cycloaddition. 

Application of the above mentioned epoxy sulfone cyclization reaction has been ingeniously used in a synthesis of muscone (Scheme 113, entries c and d) and also of vitamin D3 (Scheme 113, entry e)/ In the latter case surprisingly the terminal epoxide, when subjected to the intramolecular cyclization gave a mixture of sulfonylcyclopentane and sulfonylcyclohexane derivatives arising respectively from the epoxide ring opening at the most (30%) and the least (50%) substituted carbons. ... 

Wasserman et al. utilized an intramolecular imine-epoxide ring opening/cyclization process <88TL4973> to synthesize heterotropanes and substituted piperidines (Scheme 20). This methodology has been applied to the total syntheses of piperidine-based alkaloids (+)-teneraic acid <89TL6077> and ( )-solenopsin-A <88TL4977>. 

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