Modular Access to Substituted Azocanes via a Rhodium-Catalyzed Cycloaddition–Fragmentation Strategy

Abstract

A short entry to substituted azocanes by a Rh-catalyzed cycloaddition–fragmentation process is described. Specifically, exposure of diverse N-cyclopropylacrylamides to phosphine-ligated cationic Rh(I) catalyst systems under a CO atmosphere enables the directed generation of rhodacyclopentanone intermediates. Subsequent insertion of the alkene component is followed by fragmentation to give the heterocyclic target. Stereochemical studies show, for the first time, that alkene insertion into rhodacyclopentanones can be reversible.

Ring-opening, cycloaddition and rearrangement reactions of nitrogen-substituted cyclopropane derivatives

“…The mechanism is somewhat different in that case, with a fragmentation as one of the last elementary steps, rather than reductive elimination (Scheme 38). 128 The development of this particular work has led to the finding that not only the formation of the rhodacyclopentanone intermediate is reversible, but also the subsequent alkene insertion process. …”

Synthesis and applications of rhodacyclopentanones derived from C–C bond activation

“…In contrast, cis -1,2-disubstituted cyclopropane 51 generated solely regioisomer 53 , which derives from Rh-insertion into the more hindered proximal C-C bond (bond b ). Stoichiometric experiments confirmed, in both cases, that product regioselectivity reflects the regiochemical preference of rhodacyclopentanone formation 17,42…”

“…Using this approach, a direct and modular entry to azocanes 57 from N -cyclopropylacrylamides 54 was developed, via a formal (7+1) cycloaddition-tautomerisation sequence (Scheme 20). 42 Amide-directed C-C bond activation of 54 delivers rhodacyclopentanone 55 , and, from here, migratory insertion of the alkene affords rhodabicycle 56 . At this point, instead of C-C reductive elimination ( cf .…”

Tin(IV)-Porphyrin Tetracarbonyl Cobaltate: An Efficient Catalyst for the Carbonylation of Epoxides

“…All epoxides were stirred for a few days over CaH 2 , vacuum distilled, and degassed by freeze-pump-thaw prior to use. NaCo(CO) 4 [45], 5,6-epoxyhexanenitrile, 3,4-epoxybutyl butyrate [46], cyclohexyl oxirane [47], 2-(tert-butyl)oxirane [48], and 2-benzyl oxirane [49] were synthesized following previously reported methods.…”