Generation and trapping of 7-norbornylidenecarbene and a heptacyclic analog of this alkylidenecarbene

Generation and Trapping of a Cage Annulated Vinylidenecarbene and Approaches to Its Cycloalkyne Isomer

“…The presence of the cyclopropylidene moiety in 16 was confirmed by the fact that the two hydrogens of both the isomers are highly shielded (δ 0.63 and 0.84 for one isomer and δ 0.69 and 0.99 for the other) in 1 H NMR and the two olefinic carbons of both the isomers are separated by >30 ppm in 13 C NMR (i.e., 109.9 and 141.4 for one isomer and 110.0 and 141.5 for the other). These data for 16 correlated well with those reported for other cage vinylidenecarbene trapped products (Table ). , …”

“…These data for 16 correlated well with those reported for other cage vinylidenecarbene trapped products (Table 1). 17,18 The two isomers formed in ca. 1:1 ratio arise from approach of carbene 11 only from the exo face of the norbornene framework despite the fact that, in principle, the addition of carbene 11 to norbornene 15 could provide as many as four stereoisomeric products 16a−d (Figure 1).…”

“…Despite the detailed experimental − and theoretical − investigations on the generation, trapping, and the mechanistic implications associated with the transient existence of cycloalkynes, studies on cycloalkynes that are part of a complex framework, viz highly strained polycycles, are relatively scarce. − Owing to the high degree of strain associated with polycyclic cage hydrocarbons, cage annulated reactive intermediates often exhibit interesting and unexpected properties. For instance, in contrast to the behavior of the parent or relatively unstrained systems, − certain cage-annulated cyclopentylidenecarbenes 5 , 7 and 9 have been found to be kinetically and thermodynamically more stable than their corresponding cyclohexynes 6 , 8 and 10 , respectively (Scheme ). − While all the carbenes 5 , 7 and 9 have been generated and trapped, − their corresponding alkynes 6 , 8 and 10 , respectively, remained elusive. For instance, attempts to trap the cyclohexyne isomer 10 of carbene 9 failed as it underwent spontaneous ring contraction to 9 via 1,2-shift …”

“…Correlation of the 1 H and 13 C NMR Spectral Data of Product 16 with Analogous Compounds in Literature17,18 …”

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…Many examples of gem -dichlorocyclopropanes prepared by the addition of dichlorocarbene to unsaturated compounds have appeared recently. − Some recent examples of reactions of unsaturated hydrocarbons with dichlorocarbene are collected in Table . The superiority of the PTC method is illustrated in eq 6.…”