Addition of unsaturated carbenes to cyclic dienes. Intramolecular trapping of trimethylenemethane diradicals

Abstract

Cycloaddition reactions of pentamethyleneketene to cyclopentadiene, dihydropyran, tetramethylallene, diisopropylcarbodiimide, IV-ferf-butylbenzylimine, and chloral have been investigated as routes to spiro compounds. Pentamethyleneketene is formed in situ from the triethylamine dehydrochlorination of cyclohexanecarboxyl chloride and the zinc dehalogenation of -bromocyclohexanecarboxyl chloride. Dimerization is a serious competing reaction and reactive cycloaddition partners are necessary to successfully compete for the ketene.

Alkylidenecarbenes, Alkylidenecarbenoids, and Competing Species: Which Is Responsible for Vinylic Nucleophilic Substitution, [1 + 2] Cycloadditions, 1,5-CH Insertions, and the Fritsch−Buttenberg−Wiechell Rearrangement?

“…Unfortunately, this test was apparently not repeated in the usually employed protic solvents, thus not allowing a comparison and conclusions. The acyclic N -nitrosoacetamides 98a (with base) ,, and 98b (in boiling THF) were regarded to be more suitable starting materials than the N -nitrosooxazolidones 96 .

…”

Strain-Induced Transformations of Bicyclo[3.1.0]hex-1-enes

“…Berson and co-workers further explored Diels-Alder reactivity of bicyclo[3.1.0]hex-1-enes by employing a different precursor (Scheme 32). 5 Newman's method of generating alkylidene carbene from 5,5-dialkyl-N-nitrosooxazolidone 106 61,62 was examined. By treating 106 with aqueous sodium hydroxide in the presence of 1,3-cyclopentadiene, Diels-Alder adduct 107 and 109 was obtained, along with 44a-c.…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…Another broad family of substrates are able to produce the desired alkylidenecarbene species by decomposition of intermediate diazoalkenes or vinyldiazonium ions 80a,94a N -nitroso- N -acetyl-1,2-amino alcohols, 94a,80b (tosylazo)alkenes 76,86 and peculiar, stable vinylamines 103 have served this scope. A method for the direct production of alkylidenecarbenes from the corresponding ketones by treatment with dialkyl diazomethylphosphonate (DAMP) and bases with intervention of intermediate diazoalkenes has also been developed, 95a,b, and has found recently new synthetic applications. ,, …”