Pericyclic Reactions of Free and Complexed Cyclopentyne

Abstract

The selectivity between [2 + 2] and [2 + 4] cycloadditions of cyclopentyne with spiro[2.4]nona-2,4-diene depends on the mode of generating the cycloalkyne. Using diazomethylenecyclobutane and (bromocyclobutylidenemethyl)trimethylsilane as precursors affords cyclopentyne in an unencumbered form, whereas using dibromomethylenecyclobutane and 1,2-dibromocyclopentene yields a cyclopentyne-lithium bromide complex.

Ansa-bridged η5-cyclopentadienyl molybdenum and tungsten complexes: synthesis, structure and application in olefin epoxidation

“…The synthesis of the spiro cyclopentadiene precursor compoundspiro [4,4]nona-6,8-diene-is performed as reported in the literature. 11 Complexes 1 and 2 (Chart 1) are prepared via some modifications of the literature procedure, 12 by reacting a THF solution of the spiro cyclopentadiene with tricarbonyl complexes of the formula M(CO) 3 (CH 3 CN) 3 (M = Mo, W). Complexes 1 and 2 are isolated at −30 • C as yellow crystals.…”

Competitive Intermolecular Pericyclic Reactions of Free and Complexed Cyclopentyne

“…We recently reported [2 + 2] and [2 + 4] cycloaddition reactions involving cyclopentyne ( 1 ) and spiro-1,3-dienes ) 2b.…”

“…We recently reported [2 + 2] and [2 + 4] cycloaddition reactions involving cyclopentyne ( 1 ) and spiro-1,3-dienes ) 2b. The competition between the two reaction channels for cycloaddition, which nominally represent [2 + 2] and [2 + 4] pericyclic processes (vide infra), was strongly dependent on the precursor used to produce 1 .…”

Highly Strained Unsaturated Carbocycles

“…Continued irradiation (>254 nm) caused decarbonylation and gave ultimately the allene 24, through the intermediate 15. [19] In another example (Scheme 5C), [21,22] cyclobutanone 25 was converted into 15 via 26 using a diazomethyl-phosphonate anion generated with KH at -78°C, which was then converted into the cycloadduct 27.…”

“…[25] Furthermore, ab initio calculations proved that cyclohexyne also has diradical or dicarbene character. [21,22] Since cyclohexyne 30 is extremely reactive, it was quickly trapped in a matrix for characterization experiments as soon as synthesized. In the early 1960s, Wittig [32] showed that it is possible to obtain 30 from the debromination of 1,2-dibromocyclohexene 31 (Scheme 7) or via dehydrochlorination of 1-chlorocyclohexene 32.…”