Further Synthetic Attempts towards Calicene

Abstract

First synthetic attempts towards the so-far-unknown calicene ( 5-(cycloprop-2-en-1-ylidene)cyclopenta-1,3-diene) precursors 3-(cyclopenta-2,4-dien-1-ylidene)tricyclo[3.2.2.2 2,4 ]nona-6,8-diene (4; Scheme 1), 1,4-di(cyclopenta-2,4-dien-1-ylidene)cyclohexa-2,5-diene (5; Scheme 2), and (2-bromocycloprop-1-en-1-yl)cyclopentadiene (6; X Br; Scheme 5) are reported, which would represent very attractive compounds for gas-phase pyrolysis (4), matrix photolysis (5), and low-temperature HBr eliminations in solution (5).

Synthesis of Nitrogen-Substituted Methylenecyclopropanes by Strain-Driven Overman Rearrangement of Cyclopropenylmethyl Trichloroacetimidates

“…n -BuLi was titrated against diphenylacetic acid prior to use. 1,2,2-Tribromo-1-methylpropane, 1,1,2-tribromo-2,3,3-trimethylcyclopropane, (2-methylcycloprop-1-enyl)(4-bromophenyl)methanol ( 1a ), phenyl(2,3,3-trimethylcycloprop-1-en-1-yl)methanol ( 1c ), (2-methylcycloprop-1-enyl)(4-methoxyphenyl)methanol ( 1d ), 2-methylcycloprop-1-enyl)(4-methylphenyl)methanol ( 1e ), phenyl(2,3,3-trimethylcycloprop-1-enyl)methanol ( 8a ), and (4-bromophenyl)(2,3,3-trimethylcycloprop-1-enyl)methanol ( 8b ) were synthesized and characterized as previously reported. Other reagents were commercially available and used without further purification.…”

Recent Advances in Cyclopropene Chemistry

“…One of the abundantly used methods involves generation of cyclopropenylmetal species 3 in situ from trihalocyclopropane 2 and subsequent trapping of the former with a suitable electrophile (Scheme 7). By this means, various alkoxymethyl-, [40][41][42] alkoxyethyl-, 43 carbalkoxy-, 44 alkyl-, 45 and metal-substituted 46,47 cyclopropenes have been obtained in reasonable to good yields.…”

Generation of Bromophenyllithium Reagents from Dibromobenzenes and Addition to Carbonyl and Nitrile Electrophiles

“…Gilman first reported the mono-halogen metal exchange of general polyhalobenzenes in 1940. 6 4-Lithiobromobenzene has since been pre-pared using n-BuLi in Et 2 O [7][8][9] or THF 10 or sec-BuLi in THF. 11 It is interesting that even when using two equivalents of n-BuLi, it appears that only one halogen-metal exchange occurs.…”

“…11 It is interesting that even when using two equivalents of n-BuLi, it appears that only one halogen-metal exchange occurs. 8 Similarly, 1,3-dibromobenzene (5) has been converted to the mono-lithio reagent using n-BuLi in Et 2 O 12 or THF. 13 In the case of 1,2-dibromobenzene (6), the situation is further complicated by the ability of the lithiated species to eliminate LiBr and generate benzyne.…”