Conformations and Reactions of Bicyclo[3.2.1]oct-6-en-8-ylidene

Abstract

Bicyclo[3.2.1]oct-6-en-8-ylidene (1) can assume either the conformation of "classical" carbene 1a or that of foiled carbene 1b in which the divalent carbon bends toward the double bond. Oxadiazoline precursors for the generation of 1 were prepared, followed by photochemical and thermal decomposition as well as flash vacuum pyrolysis (FVP) of a tosyl hydrazone sodium salt precursor, to give a number of rearrangement products. Matrix isolation experiments demonstrate the presence of a diazo intermediate and methyl acetate in all photochemical and thermal precursor reactions. The major product from rearrangements of "classical" bridged carbene 1a is bicyclo[3.3.0]octa-1,3-diene as a result of an alkyl shift, while dihydrosemibullvalene formed from a 1,3-C-H insertion. In contrast, thus far unknown strained bicyclo[4.2.0]octa-1,7-diene formed by a vinyl shift in foiled carbene 1b. The experimental results are corroborated by density functional theory (DFT), MP2, and G4 computations.

Intermolecular Reactions of a Foiled Carbene with Carbonyl Compounds: The Effects of Trishomocyclopropyl Stabilization

“…Δ 3 -1,3,4-Oxadiazolines are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis. − ,− The diastereomeric precursors r - 10 and s - 10 were used separately herein to generate carbene 1 (Figure ). They were dissolved in either PhC­(O)­H or PhC­(O)­Me and heated to T = 165 °C until fully decomposed (Scheme ).…”

“…are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis [71][72][73][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115]. The diastereomeric precursors r-10 and s-10 were used separately herein to generate carbene 1(Figure 4).…”

Probing the Nature and Extent of Stabilization within Foiled Carbenes: Homoallylic Participation by a Neighboring Cyclopropane Ring

“…Oxadiazolines are quite versatile compounds and popular carbene precursors. , Depending on their substituents, they decompose by different pathways to give a variety of products. (1′ R ,2′ R ,4′ S ,5′ S )-5-Methoxy-5-methylspiro[2,5-dihydro-1,3,4-oxadiazole-2,8′-tricyclo[3.2.1.0 2,4 ]octane] ( 6 ) is expected to generate the requisite carbene 3 by either photolysis or thermolysis.…”

Approach to Loschmidt's tetracyclic benzene isomer and related tetra‐ and tricyclic isomers by intramolecular carbene additions

“…It is interesting to compare the geometries of the carbene 14 .. and its “addition” product, 15 .. , with the recently described “foiled‐reaction” carbene, 17 .. , and its putative addition product, 18 •• (Table ) . Because of the bicyclic nature of 17 .. the flap angle of the carbene is expected to be smaller (150.7° vs. 180° for 14 .. ); the “addition”, forming 18 •• is comparable to that forming 15 .. (100.8° for 18 •• vs. 100.4° for 15 .. ).…”