The synthesis of seven-membered nitrogen heterocycles by silyl-aza-Prins cyclization is described. The process provides trans-azepanes in high yields and good to excellent diastereoselectivities. Moreover, the reaction outcome is dependent on the Lewis acid employed. Thus, while azepanes are selectively obtained when InCl3 is used, the reaction in the presence of TMSOTf provides tetrahydropyran derivatives corresponding to a tandem Sakurai-Prins cyclization.

Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai-Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R(2)≠H) selectively provide oxepanes, thus corresponding to a direct silyl-Prins cyclization. Both types of product are obtained with excellent stereoselectivity. Theoretical studies have been performed to obtain some rationalization for the observed stereoselectivity.

Two families of regioisomeric 1,4-benzodiazepines, 4-benzyl-3H-benzo[e][1,4]diazepin-5-ones and 4-benzoyl-4,5-dihydro-3H-benzo[e][1,4]diazepines, have been synthesized through a similar Ugi/ reduction cyclization sequence. Their conformation and stability depend on the position of the tautomeric imine/enamine equilibrium present in the diazepine nucleus, which in turn depends on the relative position of the carbonyl group adjacent to the nitrogen at the 4-position in the benzodiazepine system.Moreover, the electrophilic center on the imine tautomer is essential for the antitumor activity of some benzodiazepines as a DNA binding position. The mechanism of tautomerization in the presence or absence of the oxo group has been studied computationally using DFT methods (B3LYP/6-31G** level).

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A hydroxypolyamide (HPA) manufactured from 2,2-bis(3-amino-4-hydroxy phenyl)-hexafluoropropane (APAF) diamine and 5′-terbutyl-m-terphenyl-4,4′′-dicarboxylic acid chloride (tBTpCl), and a copolyimide produced by stochiometric copolymerization of APAF and 4,4′-(hexafluoroisopropylidene) diamine (6FpDA), using the same diacid chloride, were obtained and used as polymeric matrixes in mixed matrix membranes (MMMs) loaded with 20% (w/w) of two porous polymer networks (triptycene-isatin, PPN-1, and triptycene-trifluoroacetophenone, PPN-2). These MMMs, and also the thermally rearranged membranes (TR-MMMs) that underwent a thermal treatment process to convert the o-hydroxypolyamide moieties to polybenzoxazole ones, were characterized, and their gas separation properties evaluated for H2, N2, O2, CH4, and CO2. Both TR process and the addition of PPN increased permeability with minor decreases in selectivity for all gases tested. Excellent results were obtained, in terms of the permeability versus selectivity compromise, for H2/CH4 and H2/N2 separations with membranes approaching the 2008 Robeson’s trade-off line. The best gas separation properties were obtained when PPN-2 was used. Finally, gas permeation was characterized in terms of chain intersegmental distance and fraction of free volume of the membrane along with the kinetic diameters of the permeated gases. The intersegmental distance increased after TR and/or the addition of PPN-2. Permeability followed an exponential dependence with free volume and a quadratic function of the kinetic diameter of the gas.