A simple and convenient synthesis of 4-methyl-3-nitro-2-trihalomethyl-2H-chromenes from N-unsubstituted imines of 2-hydroxyacetophenones and trichloro(trifluoro)ethylidene nitromethanes

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

“…Catalytic synthesis of nitrochromenes from salicylaldehydes and α,β-unsaturated nitro compounds are well documented in literature [54–59], but there are very few reports on the organocatalyzed synthesis of chiral nitrochromenes. Xu et al [60] in 2008 first reported a novel organocatalytic tandem oxa-Michael–Henry reaction between salicylaldehydes 1 and nitroalkenes 27 employing ( S )-1-methyl-2-(pyrrolidin-2-ylmethylthio)-1 H -imidazole ( VIII ) as organocatalyst in the presence of salicylic acid as cocatalyst and in DMSO as solvent (Scheme 14).…”

Synthesis of Novel 5,6‐Dihydropyrrolo[2,1‐a]isoquinolines via Grob Reaction between (E)‐1,1,1‐Trifluoro‐3‐nitro‐2‐butene and 3,4‐Dihydroisoquinolines

“…The convertibility of the nitro group into a variety of functional groups such as carbonyl (Nef reaction), oxime, hydroxylamine, amine, and hydrogen ( via desamination reaction) enhances the usefulness of the trihalomethylated nitroolefins in synthetic organic chemistry . In continuation of our studies on the chemical properties of CX 3 ‐nitroalkenes (X = F and Cl), which turned out to be highly reactive substrates in the hetero‐Diels–Alder reaction and in reactions with some N‐, O‐, and C‐nucleophiles , we decided to investigate the reaction of ( E )‐1,1,1‐trifluoro‐3‐nitro‐2‐butene ( 1 ) with 1‐methyl‐ and 1‐benzyl‐3,4‐dihydroisoquinolines 2 , which are capable of reacting with electrophilic substrates as C‐nucleophiles or 1,3‐C,N‐dinucleophiles via the enamine tautomeric form . Although much attention has been paid to the chemistry of 3,4‐dihydroisoquinolines 2 , mainly due to their use as excellent building blocks for the preparation of a variety of complex heterocyclic compounds , there is only one report on the reaction of ethyl‐(6,7‐dimethoxy‐3,4‐dihydroisoquinolin‐1(2 H )‐ylidene)acetate with 2‐nitro‐1‐phenylpropene and 1‐nitro‐1,2‐diphenylethene leading to the corresponding 5,6‐dihydropyrrolo[2,1‐ a ]isoquinoline derivatives .…”

Chiral Phosphoric Acid Catalyzed Enantioselective Transfer Hydrogenation of ortho‐Hydroxybenzophenone NH Ketimines and Applications

“…Non-coordinating solvents (such as toluene and chloroform) afforded amine 3 a with complete imine conversion and good enantioselectivities ( tion of ortho-hydroxybenzophenone in methanol with ammonia at room temperature. [13][14][15] All the ortho-hydroxybenzophenone N À H imines we prepared were quite stable at room temperature and existed exclusively as the E isomer due to the presence of an intramolecular hydrogen bond (O À H···N; d = 13.3-15.6 ppm in CDCl 3 ). These N À H imines with different substituents in ring A ( Table 2) were all well tolerated, independent of their electronic nature and positions.…”

“…[14,15] To explain the observed enantioselectivity, a model of the sevenmembered cyclic complex formed between phosphoric acid 1 d and 2 a was proposed (Figure 1). [13,16] The Si face of the imine was shielded by the lower SiPh 3 group, thus preventing attack of the Hantzsch dihydropyridine. The Re face was only shielded on the side of ring B but not on the side of ring A.…”

“…, entries[12][13][14][15][16][17][18][19][20][21] and in ring B (Table 2, entries 1-11 and 25), or in both rings (Table 2, entries 22-24) were reduced efficiently to provide the corresponding diarylmethylamines in excellent yields (80 to 91 %) and enantioselectivities (ee values from 88 up to > 99 %,Table 2). Functional groups (such as OMe, OPh, F, Cl, Br, NO 2 , CO 2 Me, and PhCO,…”