Intramolecular epoxide cleavage

As we have seen in coimection with directed intramolecular epoxide cleavage, cation stabiHty does play a very important role in regioselectivity (see 103/104) in the aUyUc epoxide discussed the charge stabilization in the allyl position is responsible for the observed endo-attack at C3. 

These data give a very strong encouragement to look for intramolecular epoxide cleavage in the presence of a cobalt complexed triple bond since this Nicholas complex has been shown to strongly favor a positive charge in the a-position to this complexed triple bond. 

An intramolecular nucleophilic epoxide cleavage of this type was used to convert 1 into 2, an intermediate in a synthesis of 3, which was originally believed to be the structure of the alkaloid cannivonine of the New Brunswick cranberry. ... 

Table 5.7. We have attempted to activate the epoxide using Lewis acids to accelerate the organometallic epoxide-opening reaction, but to no avail. Analogously, intramolecular cyclizations via an epoxide cleavage process can also be realized. For example, treatment of 6-bromo-l,2-epoxyhexane with thienyl-based copper resulted in intramolecular cyclization subsequent...

It was elaborated in connection with an enatioselective synthesis of D-erythro-sphingosine 132, starting from epoxide 126. There was the intention to use an intramolecular ring cleavage with an N-nucleophile to arrive at the amino-diol pattern present in sphingosine [41]. 

The hydrogeh atom bound to the amide nitrogen in 15 is rather acidic and it can be easily removed as a proton in the presence of some competent base. Naturally, such an event would afford a delocalized anion, a nucleophilic species, which could attack the proximal epoxide at position 16 in an intramolecular fashion to give the desired azabicyclo[3.2.1]octanol framework. In the event, when a solution of 15 in benzene is treated with sodium hydride at 100 °C, the processes just outlined do in fact take place and intermediate 14 is obtained after hydrolytic cleavage of the trifluoroacetyl group with potassium hydroxide. The formation of azabi-cyclo[3.2.1]octanol 14 in an overall yield of 43% from enone 16 underscores the efficiency of Overman s route to this heavily functionalized bicycle. 

The organocopper reagents prepared in this way cleave epoxides in high yield with substitution of the alkyl group at the less hindered site. This cleavage has been used to effect intramolecular cyclization (second example). 

The vinyl silane 247 was unmasked to the ketone 250 by epoxidation, subsequent ring opening of the epoxide with HF in pyridine and concurrent cleavage of the THP and TBS protecting group (Scheme 39). The Stork-Jung annulation was completed through the treatment of the diketone 250 with sodium methoxide to mediate the intramolecular aldol con-... 

The optically active N-aminoindoline (265) has been applied to the asymmetric synthesis of a variety of a-amino acids (70JA2476, 2488). Starting from TV-benzoyl-1,2,3,4-tetrahy-droquinaldine (257), the chloro amide (258) was prepared by von Braun cleavage. Thermolysis converted (258) to the rrans-unsaturated amide (259) which was epoxidized. On base treatment the epoxide (260) underwent intramolecular nucleophilic displacement and amide hydrolysis to afford indoline (261) stereospecifically. Resolution of (261) was accomplished via the brucine salt of the N-o-carboxybenzoyl derivative (262). Alkaline hydrolysis, N-nitrosation and reduction yielded the levorotatory 1-aminoindoline (265). Reaction of... 

Certain uneaturated fatty acids give lactone esters on treatment with peracetic acid, presumably by intramolecular attack of the carboxyl function on the initially-formed epoxide ring. Thus, 4,8-cpnxypentanoic acid generated by peracetic add oxidation of 4 pentenoie acid undergoes cleavage to give a five-membered lactone as... 

One synthesis of benzofurans is based on cyclofragmentation. An appropriately substituted sulfone is used as a nucleophile in intramolecular ring opening of an epoxide. The resulting molecule loses a sulfinate and formaldehyde. By immobilization of the sulfinate on a resin this sequence can be used for the cleavage of benzofurans from solid supports [112] (Scheme 6.1.31). 

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