Electrophiles ring opening

The electrophilic ring opening of iV-allyl HHT 53 with chloroacetyl chloride gave N-allyl- -chloromethyl-a-chloroacetamide 54, which was then alkylated with the diethyl ester of a-aminomethylphosphonic acid (AMPA) to generate the imidazolone 55. Subsequent hydrolysis of 55 gave GLYH3 (57). 

The remainder of products ( ca. 10%) are caused by electrophilic ring opening, see ref. 45. In strong acids, such as liquid HF, polymerization of benzocyclobutene is observed. See ref. 49. 

Only a limited number of examples are known of applications of thietanes in organic synthesis. Prominent among these examples would be electrophilic ring opening reactions leading to polyfunctional sulfur compounds (33)-(37), utilization of 3-thietanones (55) and metal complexes (87) derived therefrom as oxyallyl zwitterion equivalents in cycloaddition reactions, synthesis of dipeptide (63) with a /3-thiolactone, Raney nickel desulfurization of thietanes (e.g. 120 cf. Table 7) as a route to gem-dimethyl compounds, and desulfurization of thietanes (e.g. 17) in the synthesis of cyclopropanes (also see Table 7). 

C. Electrophilic Ring-opening Reactions and Insertion Reactions. 126... 

In the past decade, there has appeared only one report, which can be classified under this heading, on the monodeoxygenation of spiro-adamantane-l,2-dioxetanes induced by catalytic amounts of tris-(2,4-dibromophenyl)-aminium hexachloroantimonate <1998T6939>. An electron-transfer mechanism from the aminium salt has been proposed for the observed formation of various ketones. Reports citing the electrophilic ring opening of dioxetanes by boron trifluoride, trifluoroacetic acid, and various other Lewis acids have been summarized in CHEC-II(1996) <1996CHEC-II(1B)1041>. 

Most likely, the two main pathways consist of reactions of the electrophilic ring-opened aldehyde form of the hemiacetal with bionucleophiles and of reactions of a unique multi-centered cationic nucleophile that can be generated from DIMBOA by N-O-fission.37 Recently, we reported a novel hypothesis for the mode of bioactivity based on the formation of 3-formyl-6-methoxybenzoxazolin-2(3H)-one (FMBOA) by formal dehydration of DIMBOA.40 FMBOA was proven to be a potent formyl donor towards typical nucleophiles occurring in biomolecules and could, if formed under natural conditions, also lead to biological effects by formylation of biomolecules. The mechanism of this new dehydration was elucidated with [2-13C]-DIMBOA.33... 

Literature dealing with the electrophilic ring-opening of cyclopropenes is sparse in relation to that for the saturated analogs. The earliest review by Closs and that by Halton and Banwell (this volume) are noteworthy. The reader is referred to these reviews for more comprehensive coverage. 

Alternatively, electrophilic ring opening of the oxetane cycle by HBr produces a difunctiona-lized compound which after activation of its OH group allows for selective substitution of the leaving groups by two different nucleophiles (Scheme 1, route B, lower branch). 

Pro to nation of Cyclopropanes. Unassisted ionization does not preclude the subsequent formation of alkyl-bridged ions. Evidence for o-delocalization must then be derived from the product-forming step of the rearrangement. Useful information on this point may be obtained from the electrophilic ring opening of cyclopropanes. Several comprehensive reviews on protonated cyclopropanes are available66,4S8 460 Some observations pertinent to the present discussion will be summarized ... 

The palladium-catalyzed acylation of siloxycyclopropane furnishes a 1,4-di-carbonyl compound. A C-C bond of the three-membered ring is cleaved by an electrophilic attack of a palladium(II) species [103]. An analogous electrophilic ring opening of siloxycyclopropane was induced by various so-called ligand free transition metals such as Ag+ and Cu2+ [104]. 

Electrophilic ring opening of bicyclo[l. 1.0]butanes generally leads to mixtures of cyclobutyl, cyclopropylmethyl and allylmethyl compounds, among which the first two products dominate.The parent bicyclo[1.1.0]butane (1) is converted into cyclobutanol and cyclo-propanemethanol, without formation of any but-3-en-l-ol, upon treatment with 0.001 N sulfuric acid. Acetolysis of bicyclo[1.1.0]butane affords a mixture of all three acetates. In general, the product ratio is highly dependent on the substitution pattern of the bicyclic system. 

When the bicyclo[3.1.0]hexane rather than the bicyclo[4.1.0]heptane system was submitted to electrophilic ring opening with mercury(II) acetate, cleavage of both the inside and the outside cyclopropane bond was observed. The ratio of products 16 and 17 depended on the substituent in position 3. 

Although 1-methylcyclopropene reacted with bis(trifluoromethyI)ketene in nonpolar solvents by an ene-type reaction, in polar solvents, such as acetonitrile, a fluorinated diene 2 was produced, apparently by electrophilic ring opening followed by decarbonylation of an intermediate cyclopropanone. ... 

Interest has also continued in the structural characterisation and synthetic application of phosphine systems which are metallated at atoms other than phosphorus. The lithio-arsenide (88) has been shown to undergo electrophilic ring-opening on treatment with alkyl halides, providing a simple route to the... 

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