Carbanionic Rearrangements of Halomethylenecyclobutanes. Stereochemistry of the Migrating Group

Abstract

The unusual base-induced ring-enlargement of halomethylenecyclobutanes to 1-halocyclopentenes was examined with unsymmetrical and (13)C-labeled substrates to study regio- and stereochemical characteristics. Migration of a ring carbon atom (single migration) or simultaneous migration of a ring carbon atom and the halide (double migration) gives the ring-enlarged products. (13)C-labeling experiments established that both rearrangements occur with retention of configuration at the migrating center. These systems are suggested as models for the Fritsch-Buttenberg-Wiechell (FBW) rearrangement.

1,2-Shift of Element-Centered Groups (RnE) in Carbenoid Anions [RnECF2CFCl]−and its Relevance for Nucleophilic Vinylic Substitution: a DFT Study

“…A similar “double migration” mechanism was proposed by K.L. Erickson for the rearrangement of halocyclobutylidene carbenoid anions …”

“…Erickson for the rearrangement of halocyclobutylidene carbenoid anions. [5,26,29] The "double migration" pathway is characterized by a loose transition state, with very long CÀS and CÀCl distances, such structure may be also described as an ion triplet (Figure 8, Table 5S in the supporting information). As an important distinction from common "single" migration mechanism, the CH 3 S-group attacks the carbenoid centre with its lone pair: only one LP is left on S atom and one LP resides on C 1 according to NBO analysis.…”

Progress in the Synthesis and Transformations of Alkylidenecyclopropanes and Alkylidenecyclobutanes

“…The carbanionic ring enlargement of (halomethylene)cyclobutanes to 1-halocyclopentenes, which occurs with the intermediacy of cyclopentyne, has been investigated to ascertain the mechanism of the process and its regioselectivity. 544,545 Transition-metal catalysis coupled with the reactivity and strain of the MCBs give rise to interesting rearrangements. Indeed the reaction of methyl (3-arylcyclobutylidene)acetate 1408 with sodium tetraarylborate under the catalysis of [RhCl(cod)] 2 led to the 1,10-spirobiindane derivative 1409 in high yield through the domino process initiated by the reactive arylrhodium(I) species 1410 (Scheme 307).…”

“…The cyclobutylidenecarbene, generated by different methods, either by treatment of (dibromomethylene)­cyclobutane with n -Buli, or from (bromocyclobutylidenemethyl)­trimethylsilane and BnNMe 3 F, or from cyclobutylidenediazomethane, spontaneously rearranges to cyclopentyne, which is trapped in situ with alkenes to give [2+2] cycloaddition products. The carbanionic ring enlargement of (halomethylene)­cyclobutanes to 1-halocyclopentenes, which occurs with the intermediacy of cyclopentyne, has been investigated to ascertain the mechanism of the process and its regioselectivity. , …”

Synthesis, Crystallographic Characterization and Density Functional Study of Novel Spoke-Molecular Tetravent ethyltriphenylphosphorous Dibromide

“…For example, the (I-I) bond length in 30 . It is also used as starting material in synthesis of benzyldiphenylphosphine oxide which in turn and with other reagents, can be used for alkenes synthesis 31 .…”