The synthesis and some reactions of 1,2,2-trimethylbicyclobutane

α‐Selective Ring‐Opening Reactions of Bicyclo[1.1.0]butyl Boronic Ester with Nucleophiles

“…Protonation of 10 selectively generates tertiary cyclobutyl cation IV , which results in the carboxylate adding to the β‐position of the BCB to provide cyclobutane 11 as the major product. The relative stereochemistry of 11 was determined by X‐ray crystallography, indicating that the carboxylic acid underwent cis ‐addition across the central bond of 10 , which is in agreement with related acid‐catalyzed reactions of 1,3‐disubstituted BCBs [20b,c] . Remarkedly, the contrasting reactivity between bis‐sulfonamides and carboxylic acids was again observed in reactions of 10 , with bis‐sulfonamide 4 a exclusively forming cyclopropane 12 .…”

Some Pericyclic Reactions of Carbenes

“…That the initial suggestion was in fact correct was simultaneously confirmed by Skattebol (1970) and Moore et al, (1970) with isolation of the previously suggested bicyclobutane. Some important information about the detailed mechanism of the ring opening process has been gained by comparing the products from the tetrasubstituted carbenes (172) and (173).…”

Substituent Effects on the Ring-Opening Mechanism of Lithium Bromocyclopropylidenoids to Allenes

“…[10][11][12][13][14] The result of this competition is usually determined by the nature of substituents, [15][16][17] conformational change in the skeleton, 18,19 and electronic effects. 20 Bicyclobutanes are obtained when allene formation is difficult, for example, with bicyclo[4.1.0]heptan-7-ylidene affording 7 and 8, 21,22 with tetrasubstituted cyclopropylidenes due to steric crowding, 13,15,23 or with polycyclic cyclopropylidenes in order to avoid the generation of a bridgehead allene. 24, 25 However, it is interesting to note that the Doering-Moore-Skattebøl route does succeed for the methoxy derivative 9 of 7,7-dibromobicylo[4.1.0]heptane.…”

“…4 The mechanism of Doering-Moore-Skattebøl rearrangement was gradually uncovered and proved to involve a carbene-like intermediate, called a lithium carbenoid (2), formed through bromine-lithium exchange. 5,6 The instability and reactivity of lithium carbenoids makes them difficult to study by conventional experimental methods, although low-temperature 13 C NMR spectroscopy was used for structure determination of a few of the more stable bromoalkyllithium carbenoids which supports the notion of a loosened C-Br bond. 7 Hence, carbenoids generated by the organometallic route largely correspond with those of free cyclopropylidenes in their intramolecular reactions.…”