Copper-catalyzed room-temperature cross-dehydrogenative coupling of secondary amides with terminal alkynes: a chemoselective synthesis of ynamides.

A copper-catalyzed aerobic oxidative cross-dehydrogenative coupling reaction between secondary amides and terminal alkynes has been developed. With the aid of ligands and 3 Å molecular sieves, ynamides can be efficiently synthesized at room temperature and conveniently scaled up. A legitimate mechanism involving nitrogen-centred radicals and copper trivalent intermediates has been proposed.

One-Pot Synthesis of α-Amino Bisphosphonates from Nitriles via Tf2O/HC(OR)3-Mediated Interrupted Ritter-Type Reaction.

A versatile synthesis of α-amino bisphosphonates has been achieved through one-pot interrupted Ritter-type reaction under mild conditions. The reactive Ritter intermediate nitrilium is in situ generated by treatment of nitrile with readily accessible Tf2O/HC(OR1)3, which is trapped by phosphite ester to deliver the desired product. This protocol is efficient, scalable, and well compatible with a broad scope of substrates. In addition, plentiful characteristic JP-C couplings including unusual five-bond long-range 5JP-C and 3JP-C across quaternary carbon and hetero (N) atoms were observed in 13C NMR spectra.

Tf2O-Mediated Cyclization of 7-Enamides: Bioinspired Construction of Fused Eight-Membered Carbocyclic Enimines and Enones.

In this paper, we document the construction of functionalized and fused eight-membered carbocycles by the triflic anhydride-mediated cyclization of 7-enamides. Taking advantage of the high electrophilicity of the nitrilium ion intermediates, generated in situ from secondary N-(2,6-dimethyl)anilides, the nonactivated, trisubstituted alkene-nitrilium cyclization reactions proceeded smoothly to afford nonconjugated ß,γ-enimines (for fused 6/6/8 ring systems), conjugated α,ß-enimines (for 6/5/8), or fused 5/8 ring systems in good yields. When the cyclization reactions were followed by one-pot acidic hydrolysis, the reaction led directly to the corresponding α,ß-enones. For some substrates, the reaction afford an efficient access to pendent cyclic ß,γ-enimines/enones.

Tf2O/TTBP (2,4,6-Tri-tert-butylpyrimidine): An Alternative Amide Activation System for the Direct Transformations of Both Tertiary and Secondary Amides.

Ten types of Tf2O/TTBP-mediated amide transformation reactions were investigated. The results showed that compared with pyridine derivatives 2,6-di-tert-butyl-4-methylpyridine (DTBMP) and 2-fluoropyridine (2-F-Pyr.), TTBP can serve as an alternative amide activation system for the direct transformation of both secondary and tertiary amides. For most surveyed examples, higher or comparable yields were generally obtained. In addition, Tf2O/TTBP combination was used to promote the condensation reactions of 2-(tert-butyldimethylsilyloxy)furan (TBSOF) with both tertiary and secondary amides, the one-pot reductive Bischler-Napieralski-type reaction of tertiary lactams, and Movassaghi and Hill's modern version of the Bischler-Napieralski reaction. The value of the Tf2O/TTBP-based methodology was further demonstrated by the concise and high-yielding syntheses of several natural products.

Synthesis of Functionalized Bicyclo[2.2.2]octan-2-ones Skeleton via Tandem Process of Amino Acid Involved Formal [4 + 2] and Decarboxylative-Mannich Sequence.

An efficient approach to a functionalized bicyclo[2.2.2]octan-2-one scaffold has been developed through a one-pot cascade process including amino acid involved successive Michael addition and decarboxylative-Mannich sequence. Starting from α,ß-unsaturated ketones and amino acids, a series of desired products 7a-7m and 8a-8o were obtained with moderate yields. In addition, the tandem process was reasonably explained by the results of DFT calculations.

Double Addition of Alkynyllithium Reagents to Amides/Lactams: A Direct and Flexible Synthesis of 3-Amino-1,4-diynes Bearing an Aza-Quaternary Carbon Center.

An efficient and mild protocol for the direct and flexible synthesis of 3-amino-1,4-diynes bearing an aza-quaternary carbon from tertiary amides and lactams has been established. The one-pot method consists of in situ activation of amides with trifluoromethanesulfonic anhydride, followed by double addition of alkynyllithium reagents at a concentration of 0.5 mol·L-1 in dichloromethane. This constitutes an extension of the method of direct reductive bisalkylation of amides that allows both employing alkynyllithium reagents as the first-addition nucleophiles and incorporating an alkynyl group as the first-introduced group.

Versatile One-Pot Synthesis of Polysubstituted Cyclopent-2-enimines from α,ß-Unsaturated Amides: Imino-Nazarov Reaction.

The imino-Nazarov cyclization of the polysubstituted pentan-1,4-diene-3-imines was realized. To this aim, a one-pot procedure involving reductive alkenyliminylation of α,ß-unsaturated secondary amides with potassium organotrifluoroborates, followed by acid-catalyzed imino-Nazarov cyclization of the polysubstituted pentan-1,4-diene-3-imine intermediates, was studied systematically. This mild, operationally simple, flexible, and high-yielding protocol efficiently affords polysubstituted pentan-1,4-diene-3-imines, cyclopentenimines, and α-amino cyclopentenones, which are useful scaffolds in organic synthesis. The substituent effect at the C2 position of the polysubstituted pentan-1,4-diene-3-imines was studied by means of density-functional theory calculations. Results suggested that the electron-donating group facilitates the imino-Nazarov cyclization process.

Organocatalytic, Asymmetric Total Synthesis of (-)-Haliclonin†A.

The first total synthesis of the alkaloid (-)-haliclonin A is reported. The asymmetric synthesis relied on a novel organocatalytic asymmetric conjugate addition of nitromethane with 3-alkenyl cyclohex-2-enone to set the stereochemistry of the all-carbon quaternary stereogenic center. The synthesis also features a Pd-promoted cyclization to form the 3-azabicyclo[3,3,1]nonane core, a SmI2 -mediated intermolecular reductive coupling of enone with aldehyde to form the requisite secondary chiral alcohol, ring-closing alkene and alkyne metathesis reactions to build the two aza-macrocyclic ring systems, and an unprecedented direct transformation of enol into enone.

Total synthesis of (-)-sessilifoliamide J.

An efficient synthesis of the Stemona alkaloid (-)-sessilifoliamide J (1) in 12 steps and 7.7% overall yield from the known building block 8 is presented. The synthesis features the Corey lactonization reaction and a highly diastereoselective α-methylation reaction to build the spiro-lactone moiety.

Radical migration-addition of N-tert-butanesulfinyl imines with organozinc reagents.

A novel migration-addition sequence was discovered for the reaction of enantioenriched N-tert-butanesulfinyl iminoacetate 1a with functionalized benzylzinc bromide reagents, producing tert-leucine derivatives in excellent diastereoselectivity (dr 98:2). The absolute configurations of two new chiral centers were unambiguously assigned by chemical transformations and X-ray crystallography. In addition, the regio- and diastereoselectivities of this novel reaction were both explained through the key N-sulfinamine intermediate M6 generated by the tert-butyl radical attack on the imine. Computational analysis of this reaction process, which was performed at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31G*-LANL2DZ level, also supported our proposed two-stage mechanism.

1-Benzyl-5-ethyl-5-hy-droxy-1H-pyrrol-2(5H)-one.

The title compound, C13H15NO2, was obtained as a by-product in the Grignard reaction of malimide. The dihedral angle between the five-memebred ring (r.m.s. deviation = 0.005 Å) and the benzene ring is 67.20 (14)°. The benzene ring and the ethyl chain lie to the same side of the five-membered ring. In the crystal, mol-ecules are linked by O-H⋯O hydrogen bonds, generating C(6) chains propagating in [010].

Reductive hydroxyalkylation/alkylation of amines with lactones/esters.

We have developed a one-pot method for the direct intermolecular reductive hydroxyalkylation or alkylation of amines using lactones or esters as the hydroxyalkylating/alkylating reagents. The method is based on the in situ amidation of lactones/esters with DIBAL-H-amine complex (for primary amines) or DIBAL-H-amine hydrochloride salt complex (for secondary amines), followed by reduction of the amides with an excess of DIBAL-H. Different from the reduction of Weinreb amides with DIBAL-H where aldehydes are formed, the reduction of the in situ formed Weinreb amides yielded amines. Moreover, this method is not limited to Weinreb amides, instead, it also works for other amides in general. A plausible mechanism is suggested to account for the outcome of the reactions.

A flexible asymmetric approach to methyl 5-alkyltetramates and its application in the synthesis of cytotoxic marine natural product belamide†A.

By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, methyl 5-methyltetramate (2 a) is found in cytotoxic mirabimide E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatin 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamide A (7) has been achieved in seven steps from (S)-9, with an overall yield of 23.8 %. Not only have the structure and absolute configuration of (+)-belamide A (7) been confirmed, but also the solvent used for recording the (13) C NMR spectrum, the (13) C NMR spectrum data correlation, and optical rotation data of natural belamide A (7) have been revised.

Asymmetric synthesis of the cytotoxic marine natural product (+)-awajanomycin and its C-11 epimer.

Full details of the convergent synthetic approach to awajanomycin, and the first total syntheses of the marine natural product (+)-awajanomycin (1) and its C-11 epimer 38 by an improved 13-step approach, are described. The key elements of the synthetic strategy resided in the use of (R)-18 as the chiral building block to construct the gamma-lactone-delta-lactam core 3 and cross-olefin metathesis as the key reaction to couple the latter with the allylic alcohol segment (R- or S-4). The efficient construction of the core 3 was realized by taking advantage of the inherent multiple reactivities of the chiral building block (R)-18. A highly diastereoselective one-pot transformation of 6 to 26 was achieved in a "one stone four birds" manner. On the other hand, enantioselective synthesis of both enantiomers of the segment 4 has been undertaken by an alternative and more efficient two-step procedure. Both awajanomycin (1) and 11-epi-awajanomycin 38 have been synthesized with overall yields of 3.8% and 3.6%, respectively. Quantum chemical calculations were undertaken to reveal the low reactivity of compound 27 toward methoxycarbonylation and to get an insight into the favored conformations of the intermediates 25-27. In addition, the geometry of the side product 39 arising from the homocoupling of the allylic alcohol moiety 4 was revised as E, and an unusual cyclopropanation reaction was discovered.

A flexible approach for the asymmetric syntheses of hyacinthacines A2, A3 and structural confirmation of hyacinthacine A3.

A concise and flexible approach for the asymmetric syntheses of polyhydroxylated pyrrolizidine alkaloids hyacinthacines A(2) and A(3) has been developed using iterative reductive alkylation of O,O'-dibenzyltartarimide (5) as key steps. The ambiguity about the structure of synthetic hyacinthacine A(3) due to the differences in the NMR data of the synthetic material (2) and the natural product (hyacinthacine A(3)) was eliminated jointly by comprehensive 1D and 2D-NMR studies, and by analysis of the (1)H and (13)C NMR spectra of a mixed synthetic product and natural hyacinthacine A(3). The latter method also allowed a confirmation of the structure of the natural hyacinthacine A(3), and may be useful for structural confirmation of other hydroxylated alkaloids.

4-Bromo-2-chloro-aniline.

The title compound, C(6)H(5)BrClN, is almost planar (r.m.s. deviation = 0.018 Å). In the crystal, mol-ecules are linked by inter-molecular N-H⋯N and weak N-H⋯Br hydrogen bonds, generating sheets.

Organocatalytic, Enantioselective Reductive Bis-functionalization of Secondary Amides: One-Pot Construction of Chiral 2,2-Disubstituted 3-Iminoindoline.

We report the first catalytic, enantioselective reductive bis-functionalization of common amides, which provides a facile access to a variety of 2,2-disubstituted 3-iminoindolines in good yields and with excellent enantioselectivities. The reaction conditions are quite mild and can be run on a gram scale. In this one-pot reaction, three C-C bonds, one ring, and one nitrogen-containing tetrasubstituted carbon stereocenter are created in a catalytic enantioselective manner.

Divergent synthesis of N-heterocyclic 1,6-enynes through a zinc-catalyzed decarboxylative A3 reaction.

A zinc-catalyzed decarboxylative A3 reaction of cyclic amino acids, α,ß-unsaturated aldehydes and terminal alkynes has been developed. A series of functionalized N-heterocyclic 1,6-enynes have been successfully obtained with excellent regioselectivities through this novel approach. In addition, the utility of this straightforward process is demonstrated by the preparation of a polycyclic nitrogen-containing heterocyclic compound.

(3S,7aR)-7-Meth-oxy-7a-methyl-3-phenyl-2,3-dihydro-pyrrolo[2,1-b]oxazol-5(7aH)-one.

In the title chiral butterfly-like bicyclic lactam, C(14)H(15)NO(3), the phenyl and methyl groups are syn with respect to each other. The dihydro-pyrrrole ring adopts a boat conformation, whereas the oxazole ring has a slightly distorted boat conformation. The packing of mol-ecules in the crystal structure is stabilized by inter-molecular C-H⋯O hydrogen bonds.

Asymmetric Total Synthesis and Absolute Configuration Determination of (-)-Verrupyrroloindoline.

The first asymmetric total synthesis of (-)-verrupyrroloindoline (20% overall yield in 6 steps) is described. The short approach was enabled by Buchwald's Cu(II)-catalyzed asymmetric conjugate reduction, DMDO-triggered one-pot four-step tandem reaction, and the first amide-selective Ir-catalyzed direct reduction of ß-carboethoxy tertiary lactam. Along with the total synthesis, the absolute configuration of natural verrupyrroloindoline was determined as 7 R,10 R,11 R.