Cheap and long-life reusable polymer for asymmetric organozinc catalysis based on camphor-derived hydroxyamides.

Polystyrene grafted with a chiral zinc-complexing camphor-derived N,N-disubstituted hydroxyamide is proposed as a new type of functional polymer of high reusability for the development of sustainable organozinc-catalyzed asymmetric reactions. The main goal of this new functional polymer is the ease of the hydroxyamide-moiety preparation (cheap chiral ligand obtained straightforwardly from an enantiopure starting material coming from the chiral pool), as well as its chemical robustness when compared with other related zinc-complexing functional groups. The latter allows the polymer to be active after multiple applications, without significant loss of its catalytic activity.

Dual stereoselection in the addition of diethylzinc to benzaldehyde by using highly structurally close ligands.

The screening of the catalytic activity in the diethylzinc reaction of a series of easily accessible (1S)-ketopinic-acid derived hydroxyamides, designed by key structure modifications of a parent highly active related bis(hydroxyamide), has allowed to find the first case of dual stereoselection in highly structurally close ligands of such interesting chemically sustainable typology. The found striking dual stereoselection is explained on the basis of empiric models for the acting zinc catalysts and involved controlling transition states, which are supported by additional specific experimental structure-activity tests.

Unexpected efficiency of non-C(2) -symmetric bis(hydroxyamide)-based zinc-chelate catalysts.

Asymmetric bis(hydroxyamide)-based zinc-chelate catalysts are able to promote the enantioselective addition of diethylzinc to benzaldehyde in the absence of titanium with yields and ees comparable, or inclusively superior, to their C(2) -symmetric analogues. This unexpected fact demonstrates that the previously established assumption on the necessity of using C(2) -symmetric bis(hydrdoxyamides) to generate C(2) -symmetric zinc-chelate catalysts can be discarded, which expand the possibilities for designing new ligands based on the interesting hydroxyl-amide functional grouping.

Electron ionization mass spectral studies of bridgehead-substituted norbornan-2-ones: camphor derivatives.

The electron ionization (EI) mass spectra of a series of bridgehead-substituted 3,3-dimethylnorbornan-2-ones, derived from natural (1R)-(+)-camphor, have been studied and their cleavage mechanisms rationalized on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation (CID) tandem mass spectrometric experiments. The fragmentation patterns are very dependent on both the structural nature and the electronic properties of the bridgehead substituent. The driving force for the main fragmentation pathways are competitive cleavages of the C(1)-C(2) and C(2)-C(3) bonds directed by the bridgehead substituent and either the gem-dimethyl or carbonyl groups.

The role of the C(2) configuration and methyl substitution on the catalytic activity of novel 2,3,3- and 2,7,7-trimethyl-substituted gamma-aminonorbornan-2-ols.

A new set of optically active 2,3,3- and 2,7,7-trimethyl-substituted gamma-aminonorbornan-2-ols have been obtained from 2-methylenenorbornane-1-carbonitriles derived from (+)-camphor and (-)-fenchone and probed as chiral ligands for the enantioselective addition of diethylzinc to benzaldehyde. This has allowed the study of the structural factors influencing the chirality transfer, such as variation of the relative configuration at C(2) and steric hindrance at C(2), C(3), and C(7) positions of norbornane, which result in the observance of the important role played by the gem-dimethyl position in gamma-aminonorbornan-2-exo-ols. An empirical rationalization of the obtained experimental results has been realized on the basis of energetically-favored diastereomeric Noyori-like transition states.

Solvent and stereoelectronic effects on the solvolysis rates of oxaspirocyclopropanated 1-norbornyl triflates and related bridgehead derivatives.

The study of the stereochemical outcome of the solvolysis of oxaspirocyclopropanated 1-norbornyl triflates is highly interesting since these reactions do not lead to the usual retention or fragmentation products but only synthetically interesting rearranged products are enantiospecifically formed. There is no correlation between the experimental solvolysis rates (ln k) and the B3LYP/6-31G(d)-computed ionization energies (Delta E) of the corresponding bridgehead hydrocarbons in gas phase. However, this work demonstrates the existence of a fair linear correlation between the experimental reaction rates and the PCM//B3LYP/6-31G(d)-computed free ionization energies in solution (Delta G).

Evidence for different types of water participation in the solvolysis of 1-adamantyl, tert-butyl, and methyl chlorides from density functional theory computations.

[structure: see text] The activation energy in the gas phase (deltaE(double dagger)) and the free energy of activation (deltaG(double dagger)) in water solution for the hydrolysis of the monohydrates of methyl chloride (MeCl), tert-butyl chloride (t-BuCl), and 1-adamantyl chloride (AdCl) have been computed with the B3LYP/631-G(d) method and the polarizable continuum (PCM) solvation model. There is a fair agreement between the deltaG(double dagger) values computed by us and the experimental data. The mechanistic implications of our computations are in severe contradiction with conventional representations.

Enantiospecific access to various C(9),C(10)-disubstituted camphors: scope and limitations.

The valuable chiral sources C(9),C(10)-disubstituted camphors can be enantiospecifically obtained from the corresponding C(9)-substituted camphors by a general and straightforward synthetic method. This method involves the electrophilic treatment of a key 2-methylenenorbornan-1-ol intermediate, followed by a controlled tandem carbon-carbon double-bond addition-Wagner-Meerwein rearrangement of the norbornane framework. Discussion of the results presented suggests possible extensions and limitations of the methodology used.

Self-recognition and hydrogen bonding by polycyclic bridgehead monoalcohols.

Our interest in the relationship between the hydrogen bonding motifs displayed by monoalcohols and the properties of the solids which contain these motifs has led us to determine the crystal structures of three polycyclic bridgehead monoalcohols. One C10H16O isomer crystallises in the space group P2(1)2(1)2(1) but the three molecules which comprise the asymmetric unit are related approximately by the operations of a 3(1) screw axis. They are linked by hydrogen bonds to form an infinite helix.

C10-substituted camphors and fenchones by electrophilic treatment of 2-methylenenorbornan-1-ols: enantiospecificity, scope, and limitations.

Valuable chiral sources of C(10)-substituted camphors and C(10)-substituted fenchones can be straightforwardly obtained by treatment of an appropriate, easily obtainable, camphor- or fenchone-derived 2-methylenenorbornan-1-ol with an electrophilic reagent. The process takes place via a tandem regioselective carbon-carbon double-bond addition/stereocontrolled Wagner-Meerwein rearrangement. A complete study of the enantiospecificity, scope, and limitations of this process, as well as about the role played by the hydroxyl group attached at the C(1) bridgehead position of the starting 2-methylenenorbornan-1-ols, has been realized.

Comprehensive study of the methyl effect on the solvolysis rates of bridgehead derivatives.

The effect of a bridgehead methyl group on the hydride ion affinity in the gas phase of bicyclo[1.1.1]pent-1-yl (1+), 1-norbornyl (3+), cubyl (5+), 1-adamantyl (7+), bicyclo[2.

An Experimental and Computational Study about the Effect of a Spirocyclopropane Group on the Solvolysis Rates of Bridgehead Triflates.

7',7'-Dimethylspiro[cyclopropane-1,2'-norbornan]-1'-yl triflate (9) was obtained and its solvolysis rates in buffered 60% aqueous ethanol were determined at different temperatures. The solvolytic behavior of 9 and other bridgehead derivatives (13-17, see Table 1) was studied by force-field, semiempirical and ab initio [B3LYP/6-31g(d)] methods. Cation 9(+) is a slightly pyramidal cyclopropylcarbinyl cation in a nearly perpendicular conformation, showing an sp(2)-like hybridization.