Synthesis of α-tribromomethylamines via Mg-mediated addition of bromoform to imines

Abstract

Mg-mediated addition of bromoform to electron deficient imines such as N-sulfonylimines affords α-tribromomethylated N-sulfonylamines in good to excellent yields. The procedure could be further simplified by transforming the imine precursors, α-sulfonyl-N-tosyl- and Boc-amines, in one pot to the corresponding α-tribromomethyl derivatives. Facile removal of the Boc protecting group in nearly quantitative yield and a silver carbonate mediated monodebromination have also been demonstrated.

Metal- and Solvent-Free Synthesis of m-Terphenyls by an Iodine-Catalyzed Tandem Formal [3+3]-Cycloaddition/Oxidation

“…18 Among these strategies, [3+3]-annulation from readily available acyclic precursors has proven to be efficient (Scheme 1 ). Examples of this strategy include a base-mediated [3+3]-annulation/elimination sequence from alkylidenemalononitriles and Morita–Baylis–Hillman (MBH) acetates of nitroalkenes (Scheme 1a ); 18a NaH-mediated 1,2-addition of chalcones with MBH allyl sulfones (Scheme 1b ); 18b three-component couplings of ethyl acetoacetates, amines, and enones/chalcones catalyzed by Ca(OTf) 2 in the presence of chloranil as an oxidant (Scheme 1c ); 18c coupling of alkylamines, chalcones, and β-keto esters catalyzed by cerium(IV) ammonium nitrate to generate 1,3-diaryl-1,2,3,4-tetrahydrobenzene derivatives that are subsequently oxidized by DDQ (Scheme 1d ); 18d and cyclization between chalcones and β-enamines mediated by AlCl 3 to afford intermediate polysubstituted cyclohexa-1,3-dienes (Scheme 1e ). 18e The aforementioned reactions employ expensive metal catalysts, various reagents and oxidants, or stoichiometric amounts of base, or they have a limited substrate scope and poor yields/regioselectivity of the desired products.…”

Magnesium-Mediated Regioselective Additions of Bromoform to Quinone Methides and Aurone-Derived Azadienes

“…12 We and others have been involved in the application of Mg-CHBr3 as a convenient reagent system for addition of CBr3 group to various electron-deficient alkenes. 12 Thus, the reaction of bromoform in the presence of magnesium with nitroalkenes, 13 chalcones, 14 sulfonyl/Boc imines, 15 nitrodienes, 16 and open-chain dibenzylideneketones 16 primarily affords CBr3 adducts via conjugate addition which depending on the reaction conditions can be further selectively transformed to dibromomethylidenes, 13 cyclic orthoesters and γketoesters. 14 On the other hand, cycloalkanone derived chalcones, 17 cyclic dibenzylideneketones 16 as well as 3-olefinic oxindoles 16 furnished spiro-cyclopropanated products which underwent Lewis acid-catalyzed regioselective ring expansion to afford fused bromofurans via Cloke-Wilson rearrangement.…”

“…Encouraged by the results obtained by our group in the area of conjugate addition of bromoform to activated alkenes, [13][14][15][16][17] we Synthesis Paper / PSP / Special Topic Template for SYNTHESIS Thieme proceeded to investigate the 1,6-addition of bromoform to p-QMs. Thus, p-QM 1a bearing the parent phenyl group afforded the Michael adduct 3a in 73% yield (Table 1).…”

“…In our quest to explore the versatile reactivity of the Mg-CHBr 3 reagent system with hitherto unexplored electrophiles and alternative modes of reactivity, we have chosen p-quinone methides 18 and aurone-derived azadienes, 19 which are key scaffolds for the synthesis of complex fused and spiro-heterocycles. This is also the first report of 1,2- Encouraged by the results obtained by our group in the area of conjugate addition of bromoform to activated alkenes, [13][14][15][16][17] we proceeded to investigate the 1,6-addition of bromoform to p-QMs. Thus, p-QM 1a bearing the parent phenyl group afforded the Michael adduct 3a in 73% yield (Scheme 2).…”