Reaction of oxiranes with lithium: deoxygenation leading to olefins

New Methodology for the Conversion of Epoxides to Alkenes

“…Examples of reversible chemical modifications of alkenes that have been suggested as protecting group strategies include the hydroxylation of alkenes to glycols, which may then be reconverted to alkenes via desulfonation-decarboxylation of cyclic thionocarbonate derivatives; [3] alkene bromination followed by debromination with zinc; [4] the formation of episulfides, which can be desulfurized with phosphanes, phosphites, [5,6] or thiocyanate; [7][8][9] and the epoxidation of alkenes, followed by regeneration of the alkene using a range of reducing agents such as Li, [10] SmI 2 , [11,12] Me 2 PhSiLi, [13] dimethyl diazomalonate/Rh 2 OAc 4 , [14] and ZrCl 4 /NaI. [15] In searching for a mild and convenient method for the deoxygenation of epoxides, [16] we considered the proposed mechanism of the modified Julia olefination, [17,18] in which a metallated benzothiazole sulfone 1 reacts with a carbonyl compound to give an intermediate alkoxide 2 that undergoes a Smiles-type rearrangement via 3, leading to fragmentation with loss of SO 2 from 4 to give alkene 6 and the benzothiazol-2-olate heterocycle 5 (Scheme 1).…”

Amalgamation of Synthetic Biology and Chemistry for High-Throughput Nonconventional Synthesis of the Antimalarial Drug Artemisinin

“…Being electronically rich, the endocyclic double bond of AD ( 2 ) was expected to undergo regioselective conversion to its epoxide with electrophilic reagents like m -chloroperoxybenzoic acid ( m -CPBA), eliminating the possibility of subsequent side reactions due to its presence. The protection of active functional groups to avoid undesired chemical transformations and the recovery of the original groups after removal of the protecting groups is common practice in the synthesis of complex organic molecules. , …”

Benzylic Organometals via Reductive Metalation Procedures

“…The authors rationalized this behaviour as a result of inversion at the carbanionic benzylic center of the less stable organometallic intermediate 53 [48]. Furthermore, reductive cleavage of epoxides 51 and 52 run with Li metal in refluxing THF afforded trans-stilbene, most probably via formation of the same intermediates followed by Li 2 O elimination [49].…”

“…Reductive metalation of phenyloxirane (49) was realized at low temperature either in the presence of a stoichiometric amount of LiN or of potassium biphenylide (KB), followed by trapping of the resulting organometal (50) with an electrophile [47]. At variance with this result, the reductive lithiation of cis-or trans-2,3-diphenyloxirane (51 and 52) was run under Barbier-type reaction conditions with an excess of the metal and a catalytic amount of DTBB, leading to the formation of the same product with the same stereochemistry independently from the starting material.…”