The lithium perchlorate-induced ring opening of (S)-triphenylethylene oxide (3) with secondary amines (piperidine (a), N-methylpiperazine (b), N-phenylpiperazine (c) and morpholine (d)) takes place in a stereospecific and completely regioselective manner to afford (R)-2-(dialkylamino)-1,1,2-triphenylethanols (4a-d). These amino alcohols catalytically induce the addition of diethylzinc to benzaldehyde with high enantioselectivity at 0 degrees C and at room temperature. Ligand 4a, which provides the highest enantioselectivity at 0 degrees C, has been studied in the addition of Et(2)Zn to a family of 20 representative aliphatic and aromatic aldehydes 5a-t. For a 17-membered set of alpha-substituted substrates (5a-m,q-t), including ortho-, meta-, and para-substituted benzaldehydes, the naphthaldehydes, alpha,beta-unsaturated and aliphatic (cyclic and acyclic) aldehydes, the mean enantiomeric excess of the resulting alcohols 6a-m,q-t is 97%, whereas for three alpha-unsubstituted specimens (5n-p) the addition takes place with an enantioselectivity of 92-93%.

The reaction of the phenylacetylene−dicobalthexacarbonyl complex (2) with the 4-R-2-(2-diphenylphosphinophenyl)oxazolines 1 (R = Ph) and 4 (R = CH2CH2SCH3) leads to the selective formation of the chelated complexes 3 and 5, respectively. On the other hand, the tert-butyl-substituted phosphinooxazoline 6 acts as a monodentate ligand, and its reaction with several 1-alkyne-derived complexes (2,7−10) affords readily separable mixtures of the diastereomer nonchelated complexes 11a,b−15a,b. The interconversion rate between diastereomeric pairs is dependent on the steric bulk of the alkyne substituent, and neither 3 nor 5 epimerize at room temperature. The structures of both kinds of complexes have been ascertained by a combination of spectroscopical (IR, NMR), X-ray diffraction, and chiroptical methods; this has allowed the development of a practical procedure for the establishment of the absolute configuration of the chiral alkyne−dicobaltcarbonyl complexes obtained by the selective substitution of a carbon monoxide on one of the diastereotopic cobalt atoms. The intermolecular Pauson−Khand reaction of the chelated complexes 3 and 5 with norbornadiene respectively affords the (+) and (−) enantiomers of expected enone adduct 25, but in low enantiomeric excesses. Contrary to that, the tertiary amine N-oxide-promoted intermolecular Pauson−Khand reactions of nonchelated complexes 11a,b−13a,b give the corresponding norbornadiene- or norbornene-derived adducts both in high yields (85−99%) and enantioselectivities (93−97% enantiomeric excess), in what constitutes a substantial improvement over preexisting procedures for this reaction. The possibility of achieving chiral induction in the Pauson−Khand reaction of symmetrical alkynes (via the corresponding dicobaltpentacarbonyl complexes with ligand 6) has been demonstrated for the first time. An enantioselectivity mnemonic rule and a mechanistic model that explains the observed asymmetric sense of induction have been developed, and have been found to be in agreement with the results of model semiempirical molecular orbital calculations.

Enantiopure forms of alpha,alpha'-bis(trifluoromethyl)-9,10-anthracenedimethanol and the corresponding perdeuterated isotopomers were prepared. The conformational study was carried out by (1)H NMR, and the absolute configuration was determined by the X-ray study of the crystallized diastereoisomeric carbamate derivative. This compound was tested as a chiral solvating agent (CSA). The results showed very good discrimination for several racemic mixtures that improved other classical methods. The study of diastereomeric complexes was carried out by determination of the stoichiometry of the complex and the binding constant of the equilibrium.

Starting from D-mannitol, we have prepared several C(2)-symmetric ethanotethered bis(alpha,beta-butenolides) and studied their [2+2] photocycloaddition reaction with ethylene. The protective groups of the central diol unit have a noticeable influence on the facial selectivity of the cycloaddition, the bis(trimethylsilyloxy) derivatives showing the highest diastereoselectivity. A theoretical conformational analysis of the substrates in the ground state is in good agreement with the diastereofacial selectivity experimentally observed. The bis(photocycloadducts) have been converted into the enantiopure cyclobutanes formally derived from the photoreaction of ethylene with gamma-hydroxymethyl-alpha,beta-butenolide, in which only a moderate facial selectivity had been previously found. As an application of these studies, we have developed a highly efficient and stereoselective synthesis of (+)-grandisol.

The [2 + 2] photocycloaddition of acetylene to chiral 2(5H)-furanones was investigated. The influence on the chemical yield and facial diastereoselectivity of the substituent at the stereogenic center and also the effect of a 4-methyl group were evaluated. A mechanistic proposal based on a simple theoretical conformational analysis is presented. Using a C(2)-symmetric bis(lactone) as the substrate, a diastereomeric excess higher than 98% was found.

The title compound, (C7H70)2TeI2 (or Ci4Hi41202Te), crystallizes in space group Pi, either with Z = 8, (Ia), or Z = 4, (Ib). The six independent molecules [four in (Ia) and two in (Ib)] have very similar structures. The geometry at the Te atoms is pseudo-trigonal bipyramidal, with the I atoms in the axial positions and the anisyl groups and the lone pair of electrons in the equatorial plane. The Te--C and Te--

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Hexacarbonyl dicobalt complex of bis(tert-butylsulfonylethyne) [Co2(μ-ButSO2C)2(CO)6, 3] experiences a thermally induced ligand exchange process with methyl p-tolyl sulfide, dibenzyl sulfide, and diethyl sulfide to give the corresponding stable sulfide complexes [Co2(μ-ButSO2C)2(CO)5SR2] 4, 5, and 6, respectively, in good yield (59−65%). The reaction with tetrahydrothiophene gives a disubstituted complex 7 in 74% yield. Oxathiane 9, derived from (+)-(2R)-10-mercaptoisoborneol, also reacts with 3 to generate a chiral sulfide complex 8 (58%). The solid-state structures of 5 and 8 have been established by X-ray crystallography and reveal the preference of the incoming sulfur ligand to occupy an equatorial coordination site. Further structural studies on 5 have been performed by low-temperature 1H NMR analysis and by theoretical procedures at the PM3(tm) level of theory. Analysis of the low-temperature 1H NMR spectrum of 5 shows a signal splitting consistent with the freezing of an equilibrium between two equatorially coordinated sulfides, and the computational study of the different isomers of 5 shows that the equatorially coordinated complex is 3.9 kcal mol-1 lower in energy than the most stable axially coordinated one, in agreement with solid-state and solution studies. Finally, ligand exchange experiments have been performed in order to provide an explanation for the Pauson−Khand reactivity of alkynes containing ancillary sulfide ligands and were found to support the experimentally observed rate enhancements.