Chemoselective and stereoselective lithium carbenoid mediated cyclopropanation of acyclic allylic alcohols

Abstract

The reaction of geraniol with different lithium carbenoids generated from n-BuLi and the corresponding dihaloalkane has been evaluated. The reaction occurs in a chemo and stereoselective manner, which is consistent with a directing effect from the oxygen of the allylic moiety. Furthermore, a set of polyenes containing allylic hydroxyl or ether groups were chemoselectively and stereoselectively converted into the corresponding gem-dimethylcyclopropanes in one single step in moderate to good yields mediated by a lithium carbenoid generated in situ by the reaction of n-BuLi and 2,2-dibromopropane.

Modular and Chemoselective Strategy for Accessing (Distinct) α,α‐Dihaloketones from Weinreb Amides and Dihalomethyllithiums

“…In this sense, we appreciated once more the high chemoselective profile of the acylic substitution on a nitrile bearing material ( 34 ), as well as, on ether, thioether, alkyl or aryl presenting species ( 35 – 38 ). The terminal vinyl motif – potentially representing a cyclopropyl precursor with carbenoid reagents [35] – remained unaffected during the sequence ( 39 ). With much of our delight the dibromomethylation reaction proceeded with excellent chemocontrol not only in the case of an ester‐containing substrate ( 40 ) but, more intriguingly also in the cases of carboxamide‐substituted frameworks.…”

“…A series of aromatic functionalized analogues were uniformly prepared in high yield, regardless the modulating effect displayed by the substituents on the ring (33). In this sense, we appreciated once more the high chemoselective profile of the acylic substitution on a nitrile bearing material (34), as well as, on ether, thioether, alkyl or aryl presenting species (35)(36)(37)(38). The terminal vinyl motif -potentially representing a cyclopropyl precursor with carbenoid reagents [35] -remained unaffected during the sequence (39).…”

Homologation chemistry with nucleophilic α-substituted organometallic reagents: chemocontrol, new concepts and (solved) challenges

“…is significant considering that similar carbenoids could add in a 1,4-fashion as documented by Phillips 38 and Hernández-Galán. 39 It is conceivable that LiBr may not only exert a stabilizing effect on the carbenoid, but also display a mild Lewis acid activity enhancing the electrophilicity of the carbonyl-carbon. 40 Notably, mesomeric effects can govern the chemoselectivity in particular instances, as observed in the case of chromone (formal 1,4-addition).…”

Synthesis and Performance of Strained Multicyclic Hydrocarbons as Highly Potential High-Energy-Density Fuels

“…The three-membered ring can be synthesized through Simmons–Smith cyclopropanation of alkenes using metal carbenoids. − Lithium carbenoid LiCH 2 X (X = Br or I) and samarium carbenoid ISmCH 2 I/ISmCH 2 Cl show low reactivity, and thus, high dosages are needed to get high yield. In addition, the thermal-sensitive carbenoids need to be synthesized at very low temperature (<−50 °C), − which brings difficulties in operation.…”