Cyclopropyl Ring Opening Research Articles

Photochemical oxetan formation: the Paterno–Büchi reaction of aliphatic aldehydes and ketones with alkenes and dienes

The photochemistry of four aldehydes (acetaldehyde, pivalaldehyde, and cyclopropane- and cyclobutane-carbaldehyde) and two ketones (isopropyl and cyclopropyl methyl ketone) in the presence of various alkenes, viz.(Z) and (E)-penta-1,3-diene, 2,3-dimethylbut-2-ene, (Z)-but-2-ene, (E)-1,2-dicyanoethylene, styrene, cyclopropylethylene, 1,1-dicyclopropylethylene, and dicyclopropylmethylenecyclopropane upon irradiation at 310 nm has been studied. With the aldehydes, oxetan formation dominates over other reactions, such as alkene (Z)–(E) isomerization alkene dimerization, aldehyde dimerization with formation of an acyloin, and abstraction of allylic hydrogens from the alkene by the aldehyde with formation of a hydroxy-compound. Twenty-nine oxetans have been identified. The mechanism of oxetan formation has been discussed with special emphasis on (i) the nature of the reacting excited state (the reacting excited state is the 1n–π* state of the carbonyl compound), (ii) the intermediacy of exciplexes and 1,4-diradicals, (iii) the stereospecificity, (iv) the regiospecificity, and (v) the absence of cyclopropyl ring opening.

Stable carbocations. Part X. Generation, observation, and reactions of ferrocenyl-stabilised cyclopropylalkylium and related ions

In trifluoroacetic acid solutions, 1-ferrocenyl-1-cyclopropylalkylium ions are stable and show no tendency towards rearrangement. When these solutions are quenched with aqueous sodium carbonate, mixtures of products are formed including those of cyclopropyl ring opening. In the same acid solvent, 4-ferrocenylbut-3-en-1-ols undergo protonation giving 1-ferrocenyl-4-hydroxyalkylium ions which are slowly converted into their O-trifluoroacetyl derivatives. On deprotonation, the former ions give 2-ferrocenyltetrahydrofurans; the latter afford mainly the trifluoroacetates of the starting ferrocenylbutenols. Hydrolysis of these esters in acetate-buffered aqueous acetone gives alcohols without rearrangement.

Electrocyclic effects in solvolysis. I. Aryl participation and cyclopropyl ring opening in the solvolysis of exo-3,3-diaryltricyclo[3.2.1. 0.2,4]oct-8-yl tosylates

Electrocyclic effects in solvolysis. I. Aryl participation and cyclopropyl ring opening in the solvolysis of exo-3,3-diaryltricyclo[3.2.1. 0.2,4]oct-8-yl tosylates