Barriers to inversion at nitrogen in bicyclic amines and hydrazines

Nitrogen inversion barriers have been measured for 7-chloro-1,7-diazabicyclo-[2.2.1] heptane and [2.2.2]octane; the unusual nature of the bridging nitrogen in bicyclo [2.2.11 systems is discussed.     

cis-Fused bicyclic sugar thiocarbamates. Reactivity towards amines

1,2-cis-Fused bicyclic sugar thiocarbamates of gluco and manno configurations have been prepared by treatment of the corresponding O-unprotected amino sugars and glycopyranosyl amines with thiophosgene. The reactivity of these compounds towards amines has been studied in order to determine whether these compounds could act as latent isothiocyanates; it is shown that 1,2-cis-fused bicyclic sugar thiocarbamates are more stable than their trans analogues, and are not transformed into thioureas upon treatment with amines. An unprecedented isomerization of a peracetylated glucopyranoso[2,1-d]oxazolidine-2-thione into a glucopyranoso[2,1-d]thiazolidin-2-one in DMF is also reported. The structure of this thiazolidin-2-one was confirmed by X-ray crystallography.     

Chiroptical properties of cyclic amines

Chiroptical properties of several 2 or 3 monosubstituted azetidines, pyrrolidines and piperidines as free bases and N-[2-pyridyl N-oxide] derivatives has been examined. The absolute configuration can be unambiguously established, independently on the nature of the substituent and the size of the ring, only for 2-substituted N-[2-pyridyl N-oxide]amine derivatives. This behaviour is explained in terms of limited rotational freedom in these compounds.     

Unusual deshielding of 15N in bicyclic amines and hydrazines

The bridging nitrogen in 7-aza- and 1,7-diazabicyclo[2 2.1]heptanes and unsaturated derivatives shows unusually large deshielding in the ¹⁵N NMR.     

Synthesis of medium-ring bicyclic diamines by the alkylation and cleavage of cyclic amidines

1,6-Diazabicyclo[4.3.3]dodecane (7), 1,6-diazabicyclo[4.3.2]undecane (8) and 1,8-diazabicyclo[6.3.3]tridecane (9) have been made by reduction of tricyclic α-aminoammonium salts with LiAlH₄; the protonation and oxidation of 8 and 9 are discussed.     

Nitrogen inversion in 3,6-dihydro-1,2-oxazines

The nitrogen inversion barriers of nine 3,6-dihydro-1,2-oxazines are discussed. Polar solvents were found to increase the nitrogen inversion barriers which, in turn, decrease with increasing size of the N-substituent.     

A Mitsunobu reaction to functionalized cyclic and bicyclic N-arylamines

The scope of an unexpected Mitsunobu cyclisation to prepare N-arylated Fsp³-enriched azacycles was investigated. In the current study, we have identified whether a pKa-dependent Mitsunobu cyclodehydration or a pKa-independent Mitsunobu intramolecular reaction was in operation. A Mitsunobu reaction, creating a leaving group, followed by intramolecular nucleophilic displacement was determined to be the dominant pathway.     

Electrochemical fluorinatior of some cyclic tertiary amines

Electrochemical fluorination of N,N-diethylcyclohexylamine and N-ethyldicyclohexylamine gave the corresponding F-amines together with several other compounds arising from incomplete fluorination and fragmentation reactions. In the case of N,N-diethylcyclohexylamine yields of 51–52% were obtained and most of the reaction products were isolated and identified. With N-ethyldicyclohexylamine a lower yield (16%) was observed; the resultant reaction mixture was too complex to allow the identification of its components. Comments are made about the reaction mechanism, and NMR and IR data are reported for identified compounds.     

Asymmetric synthesis of 2-substituted cyclic amines

Cyanomethylenetributylphosphorane-mediated ring closure for the asymmetric synthesis of 2-substituted cyclic amines such as azetidines, pyrrolidines and a piperidine is reported. The desired stereochemistry at the 2-position was fixed using (S)-tert-butyl sulfinamide as a chiral auxiliary.     

Catalytic kinetic resolution of cyclic secondary amines

The catalytic resolution of racemic cyclic amines has been achieved by an enantioselective amidation reaction featuring an achiral N-heterocyclic carbene catalyst and a new chiral hydroxamic acid cocatalyst working in concert. The reactions proceed at room temperature, do not generate nonvolatile byproducts, and provide enantioenriched amines by aqueous extraction.     

Condensation of fluorine-substituted benzaldehydes with amines and cyclic ketones

Condensation of fluorine-containing benzaldehydes with naphthalen-2-amine or quinolin-6-amine and cyclic ketones (cyclopentanone, cyclohexanone, and 4-methylcyclohexanone) gave new fluorine-containing derivatives of cyclopenta[c]benzo[f]quinoline, benzo[a]phenanthridine, and cyclopenta[a]- and benzo[a]-[4,7]phenanthroline. Intermediate products, 2-[(fluorophenyl)(2-naphthylamino or quinolin-6-ylamino)methylidene] cyclohexanones, dihydrobenzo[f]quinolines, and dihydro-4,7-phenanthrolines, were isolated.     

Oxidative decarboxylation of cyclic amino acids and dehydrogenation of cyclic secondary amines with iodosobenzene

Cyclic amino acids L-proline, pipecolinic acid and L-2-pyrrolidinone-5-carboxylic acid undergo oxidative decarboxylation with iodosobenzene in various solvents (including water) to yield the lactam and imide in the latter case. The reaction proceeds via initial imine formation.     

Surface active properties of simple cyclic and heterocyclic amines in water

The surface tension of aqueous solutions of simple cyclic, heterocyclic and aromatic amines was measured with a Du N?uy tensiometer at 25 degrees C and the results discussed in terms of structure-aggregation relationships. The simple compounds used in this study were piperazine, piperidine, morpholine, 3-methylpyridine, cyclohexylamine and benzylamine, with carbon numbers ranging from four to seven. Piperazine, piperidine and morpholine did not form micellar associations but cyclohexylamine, benzylamine and 3-methylpyridine did, indicating that more than six carbons are necessary to form micellar associations, at least for compounds having a six-membered ring.     

Open, cyclic, and bicyclic compounds of double silylated phosphorus and boron

Salt elimination reactions of tris(trimethylsilyl)silyl potassium (1), and two 1,4-dipotassiooligosilanes (3, 5) with 2,2,6,6-tetramethylpiperidinodichloroborane and diethylaminodichlorophosphane have generated open (2), cyclic (4) and bicyclic (6) bora- and phosphaoligosilanes. A monosilylated phosphane and the two five-membered cyclosilanes have been subjected to single crystal X-ray diffraction analysis.