1, 3-Cycloadditions to Highly Substituted, Strained Double Bonds: Spiro ?-lactams from ?-methylidene-?-lactams by reactions with diphenylnitrilimine, acetonitrile oxide, nitrones, and diazomethane

Synthesis of β-Amino Acid Derivatives via Enantioselective Lewis Base Catalyzed N-Allylation of Halogenated Amides with Morita-Baylis-Hillman Carbonates

Trifluoro- and trichloroacetamides serving as pronucleophiles undergo enantioselective Lewis base catalyzed N-allylation with Morita-Baylis-Hillman carbonates to produce enantioenriched β-amino acid derivatives. The reactions proceed as a kinetic resolution to give the allylation products and the remaining carbonates in good yields and high enantioselectivity. The obtained products are amenable to diastereoselective derivatization to produce a library of spiro-isoxazoline lactams.

Regioselective Cycloaddition of Nitrile Imines to 5-Methylidene-3-phenyl-hydantoin: Synthesis and DFT Calculations

Nitrile imine cycloaddition to hydantoins containing an exocyclic C=C double bond has been previously described in a very limited number of examples. In this work, regioselective synthesis of spiro-pyrazoline-imidazolidine-2,4-diones based on a 1,3-dipolar cycloaddition reaction of nitrile imines to 5-methylidene-3-phenyl-hydantoin have been proposed. It was found that, regardless of the nature of the aryl substituents at the terminal C and N atoms of the C-N-N fragment of nitrile imine (electron donor or electron acceptor), cycloaddition to the 5-methylidenhydantoin exocyclic C=C bond proceeds regioselectively, and the terminal nitrogen atom of the nitrile imine connects to the more sterically hindered carbon atom of the double bond, which leads to the formation of a 5-disubstituted pyrazoline ring. The observed cycloaddition regioselectivity was rationalized using DFT calculations of frontier molecular orbital interactions, global CDFT reactivity indices, and minimum energy paths.

Synthesis of novel chiral spiro-β-lactams from nitrile oxides and 6-(Z)-(benzoylmethylene)penicillanate: batch, microwave-induced and continuous flow methodologies

The first examples of the diastereoselective 1,3-dipolar cycloaddition reaction of nitrile oxides and 6-alkylidene penicillanates leading to chiral spiroisoxazoline-penicillanates are reported. The synthesis of this new type of penicillanate involved the selective generation of two consecutive stereogenic centers, including a quaternary chiral center. Furthermore, the present work also describes the outcomes of these 1,3-dipolar cycloaddition reactions under three distinct reaction conditions (conventional heating, microwave irradiation and continuous flow). The successful use of the continuous flow technique as well as the proper selection of the reaction media allowed the development of a sustainable route to chiral spiroisoxazoline-penicillanates.

The first examples of the diastereoselective 1,3-dipolar cycloaddition reaction of nitrile oxides and 6-alkylidene penicillanates leading to chiral spiroisoxazoline-penicillanates are reported.

Regioselective Synthesis and Stereochemical Structure of 1,2,8,9,13-Pentaazadispiro[4.1.4.3]Tetradeca-2,9-Dien-6-Ones

A facile regioselective synthetic approach towards 1,3,4,8,10,11-hexaaryl-13-methyl-1,2,8,9,13-pentaazadispiro [4.1.4.3]tetradeca-2,9-dien-6-ones 3a–g was achieved through the reaction of 3,5-bis(arylmethylene)-1-methyl-4-piperidinones 1a–f with nitrilimines (generated in situ by triethylamine dehydrohalogenation of the corresponding hydrazonoyl chlorides 2a,b). The stereochemical configuration of the isolated products was established to be 4 S, 5 R, 7 R, 11 S based on a single crystal X-ray diffraction study of 3b.

Regioselective Synthesis of Spiro[Naphthalene-2(1H),3′-[3H]Pyrazol]-1-Ones Utilizing 1,3-Dipolar Cycloaddition of Nitrilimines

1,3-Dipolar cycloaddition reaction of nitrilimines to a variety of 2-arylmethylidene-3,4-dihydro-1-naphthalenones 1a–h afforded the corresponding spiro[naphthalene-2(1 H),3′-[3 H]pyrazol]-1-ones 3 and not the isomeric spiro[naphthalene-2(1 H),4′-[4 H]pyrazol]-1-ones 4, in high regioselectivity. The structure of the isolated products was established through different spectroscopic techniques and confirmed via HMBC.