Rhodium(I)-Catalyzed Regioselective Ring- Expanding Rearrangement of Allenylcyclopropanes into Methylenecyclopentenes

Abstract

A highly regioselective C-C bond cleavage of the cyclopropane rings occurs in substituted allenylcyclopropanes in the presence of cationic rhodium(I) complexes. Thus, ring expansion of readily accessible allenylcyclopropanes can be achieved to give 3-methylenecyclopentenes, which could have applications as multifunctional synthetic building blocks.

Rh(II)-Catalyzed Alkynylcyclopropanation of Alkenes by Decarbenation of Alkynylcycloheptatrienes

“…A range of allenylcyclopropanes were assembled while keeping the diastereomeric ratio intact after the isomerization process. This grants easy access to another type of versatile synthetic intermediates, avoiding the use of synthetically challenging 7-allenyl-1,3,5-cycloheptatrienes, which have not been described so far. All these new reactions, together with previous reports on the use of alkynylcyclopropanes in the discovery of novel methodologies, − highlight the versatility and potential of these now readily accessible compounds.…”

Palladium-catalyzed enantioselective rearrangement of dienyl cyclopropanes

“…29 However, compared with cycloaddition, VCP rearrangement has been largely overlooked since its discovery in 1959 due to the necessity for harsh conditions (normally proceeds at 300-500 °C). [30][31][32][33][34][35] Only a handful of studies have been reported regarding VCP rearrangement under mild conditions catalyzed by transition metals such as Rh, [36][37][38][39] Pd, [40][41][42] Ni, [43][44][45] and Cu, [46][47][48] that proceed via coordination of the metal catalyst to the vinyl substituent of VCP. Nevertheless, the direct enantioselective rearrangement of VCP has remained a formidable challenge and the development of strategies for achieving this objective is highly desirable.…”

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

“…The rearrangement of VCPs to cyclopentenes and dienes are well known processes [18–25] that occur thermally or under catalysis by various transition metals including Rh, Ni, Pd, Cu, Cr, Mo, and Fe [26–34]. To date the metal-catalyzed rearrangement of azaheterocyclic VCP has not been reported.…”

“…In the context of our interest in the VCP chemistry of spirocyclopropane-annelated heterocyclic compounds [35], we started to investigate some metal-catalyzed rearrangements. The first choice was the readily available so-called Wilkinson catalyst Rh(PPh 3 ) 3 Cl, because of its documented efficiency in catalyzing the rearrangement [26] and of the possibility to extend its use to other interesting transformations, such as the [5 + 2] cycloadditions of vinylcyclopropanes to alkynes developed by Wender and co-workers [36–37]. It is known, that rhodium-catalyzed rearrangements of unactivated VCPs, without any functional substituent, usually afford dienes.…”