1569-50-2

Aerobic Pd(AcO)2/pyridine-catalyzed oxidation of unprotected carbohydrate-based terminal alkenes was studied. In accordance with previous reports, the initial reaction step gave methyl ketones. However, our substrates partially gave subsequent α,β-water elimination and alcohol oxidation to α,β-unsaturated 2,5-diketones. Upon increasing the pressure of O2, the reaction was shifted toward formation of α,β-epoxy-2-ketones. The reactions were stereoselective and gave up to quantitative conversions. However, isolated yields were substantially lower because of the complexity of the product mixtures.

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Such an asymmetric -Wittig variant that is both highly enantio- and erythro-selective is described within the context of the chiral synthesis of the insect pheromones, (3S,4S)-4-methyl-3-heptanol and (S)-4-methyl-3-heptanone.

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We describe the highly selective palladium catalyzed kinetic resolutions of the racemic cyclic allylic carbonates rac-1a-c and racemic acyclic allylic carbonates rac-3aa and rac-3ba through reaction with tert-butylsulfinate, tolylsulfinate, phenylsulfinate anions and 2-pyrimidinethiol by using N,N′-(1R,2R)-1,2-cyclohexanediylbis[2-(di-phenylphosphino)-benzamide] (BPA) as ligand. Selectivities are expressed in yields and ee values of recovered substrate and product and in selectivity factors S. The reaction of the cyclohexenyl carbonate 1a (≥99% ee) with 2-pyrimidinethiol in the presence of BPA was shown to exhibit, under the conditions used, an overall pseudo-zero order kinetics in regard to the allylic substrate. Also described are the highly selective palladium catalyzed asymmetric syntheses of the cyclic and acyclic allylic tert-butylsulfones 2aa, 2b, 2c, 2d and 4 a - c, respectively, and of the cyclic and acyclic allylic 2-pyrimidyl-, 2-pyridyl-, and 4-chlorophenylsulfides 5aa, 5b, 5ab, 6aa - ac, 6ba and 6bb, respectively, from the corresponding racemic carbonates and sulfinate anions and thiols, respectively, in the presence of BPA. Synthesis of the E-configured allylic sulfides 6aa, 6ab, 6ac and 6bb was accompanied by the formation of minor amounts of the corresponding Z isomers. The analogous synthesis of allylic tert-butylsulfides from allylic carbonates and tert-butylthiol by using BPA could not be achieved. Reaction of the cyclopentenyl esters rac-1da and rac-1db with 2-pyrimidinethiol gave the allylic sulfide 5c having only a low ee value. Similar results were obtained in the case of the reaction of the cyclohexenyl carbonate rac-1a and of the acyclic carbonates rac-3aa and rac-3ba with 2-pyridinethiol and lead to the formation of the sulfides 5 ab, 6 ab, and 6 bb, respectively. The low ee values may be ascribed to the operating of a "memory effect", that is, both enantiomers of the substrate give the substitution product with different enantioselectivities. However, in the reaction of the racemic carbonate rac-1 a as well as of the highly enriched enantiomers la (≥99% ee) and ent-1a (≥99% ee) with 2-pyrimidinethiol the ee values of the substrates and the substitution product remained constant until complete conversion. Similar results were obtained in the reaction of the cyclic carbonates rac-1a, ent-1a (≥99% ee) and ent-1c (≥99% ee) with lithium tert-butylsulfinate. Thus, in the case of rac-1a and 2-pyrimidinthiol and tert-butylsulfinate anion as nucleophiles the enantioselectivity of the substitution step is, under the conditions used, independent of the chirality of the substrate; this shows that no "memory effect" is operating in this case. Hydrolysis of the carbonates ent-1a-c, ent-3aa and ent-3ba, which were obtained through kinetic resolution, afforded the enantiomerically highly enriched cyclic allylic alcohols 9a-c (≥99% ee) and acyclic allylic alcohols 10a (≥99% ee) and 10b (99% ee), respectively.

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Supramolecular catalysts emulate the mechanism of enzymes to achieve large rate accelerations and precise selectivity under mild and aqueous conditions. While significant strides have been made in the supramolecular host-promoted synthesis of small molecules, applications of this reactivity to chemoselective and site-selective modification of complex biomolecules remain virtually unexplored. We report here a supramolecular system where coencapsulation of pyridine-borane with a variety of molecules including enones, ketones, aldehydes, oximes, hydrazones, and imines effects efficient reductions under basic aqueous conditions. Upon subjecting unprotected lysine to the host-mediated reductive amination conditions, we observed excellent ?-selectivity, indicating that differential guest binding within the same molecule is possible without sacrificing reactivity. Inspired by the post-translational modification of complex biomolecules by enzymatic systems, we then applied this supramolecular reaction to the site-selective labeling of a single lysine residue in an 11-amino acid peptide chain and human insulin.

A stereo-divergent synthesis of natural and unnatural opines in stereochemically pure form is based on the direct palladium-catalyzed N-allylation of α-amino acid esters (up to 97 % ee or 99 : 1 d.r.) using methyl (E)-2-penten-4-yl carbonate in the presence of only 1 mol% of a catalyst, prepared in-situ from the C2-symmetric diphosphine iPr-MediPhos and [Pd(allyl)Cl]2. Selected target compounds (incl. a derivative of the drug enalapril) were efficiently obtained from the N-allylated intermediates by oxidative cleavage (ozonolysis) of the allylic C=C bond under temporary N-Boc-protection.

The present invention relates to a process of hydrogenating an aIkynoI selectively to an alkenol by hydrogen using a hydrogenation catalyst which is palladium supported on a carrier in the presence of an additive which is an organic phosphorus compound bearing either a phosphine or a phosphine oxide group and with the proviso that if the additive bears a phosphino group that the additive bears two or more phosphino groups.

Two enantioselective total syntheses of the nortriterpenoid natural product rubriflordilactone A are described, which use palladium- or cobalt-catalyzed cyclizations to form the CDE rings, and converge on a late-stage synthetic intermediate. These key processes are set up through the convergent coupling of a common diyne component with appropriate AB-ring aldehydes, a strategy that sets the stage for the synthetic exploration of other members of this family of natural products. Two in one: Two enantioselective total syntheses of the nortriterpenoid natural product rubriflordilactone A are described, which use palladium- or cobalt-catalyzed cyclizations to converge on a late-stage synthetic intermediate. These key processes are set up through the coupling of a common diyne component with appropriate AB-ring aldehydes, a strategy that enables a broad exploration of this family of natural products, as well as synthetic analogues.

Gold(I)-catalysed direct allylic etherifications have been successfully carried out with chirality transfer to yield enantioenriched, γ-substituted secondary allylic ethers. Our investigations include a full substrate-scope screen to ascertain substituent effects on the regioselectivity, stereoselectivity and efficiency of chirality transfer, as well as control experiments to elucidate the mechanistic subtleties of the chirality-transfer process. Crucially, addition of molecular sieves was found to be necessary to ensure efficient and general chirality transfer. Computational studies suggest that the efficiency of chirality transfer is linked to the aggregation of the alcohol nucleophile around the reactive π-bound Au-allylic ether complex. With a single alcohol nucleophile, a high degree of chirality transfer is predicted. However, if three alcohols are present, alternative proton transfer chain mechanisms that Erode the efficiency of chirality transfer become competitive.

The tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor rhodium carbenoids and chiral allyl alcohols is a convergent C-C bond forming process, which generates two vicinal stereogenic centers. Any of the four possible stereoisomers can be selectively synthesized by appropriate combination of the chiral catalyst Rh2(DOSP)4 and the chiral alcohol.

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Copper bottomed: The application of a previously described process of dynamic kinetic asymmetric transformation to acyclic substrates allowed the identification of a relevant kinetic process in the title reaction (see scheme; CuTC= copper(I) thiophencarboxylate, Naphth= naphthyl). The optimization of the reaction conditions and generality of the method, as well as mechanistic considerations are disclosed.

This manuscript describes the extension of Stille's palladium-catalyzed olefin dicarbonylation reaction to chiral allylic alcohols with chirality transfer to afford the corresponding chiral alcohol functionalized with bis-carbomethoxy esters, containing three contiguous chiral centers, in good to excellent diastereoselectivities (78-98%).

Chemical equation presented Allylic sulfamides undergo aerobic oxidative cyclization at room temperature, mediated by a Pd(O 2CCF3)2/DMSO catalyst system in tetrahydrofuran. The cyclic sulfamide products are readily converted into 1,2-diamines, and substrates derived from chiral allylic amines cyclize with very high diastereoselectivity.

Making chairs: A kinetic resolution of allylic imidates by planar chiral palladacycles is described which is the result of high face selectivity for olefin coordination to the catalyst and inherent substrate selectivity. These studies confirm that planar chiral palladacycles mainly operate via (half)chair-like transition states/intermediates.

Application of an in situ generated bulky palladium(II) hydride catalyst obtained from a 1:1:1 mixture of Pd(dba)2, P(tBu)3, and isobutyryl chloride provides an efficient protocol for the isomerization and migration of a variety of olefins. In addition to the isomerization of (Z)- to (E)-olefins, the conjugative migration of allylbenzenes, allyl ethers, and amines was effectively achieved in near-quantitative yields and with excellent functional group tolerance. Catalyst loadings in the range of 0.5-1.0 mol % were typically applied, but even loadings as low as 0.25 mol % could be achieved when the reactions were performed under neat conditions. More interestingly, the investigated catalyst proved to be selective for converting terminal alkenes to 2-alkenes. This one-carbon migration process for monosubstituted olefins provides an alternative catalyst, which bridges the gap between the allylation and propenylation/vinylation protocols. Several substrates, including homoallylic alcohols and amines, were selectively transformed into their corresponding 2-alkenes, and examples using enantiomerically enriched substrates provided products without epimerization at the allylic stereogenic carbon centers. Finally, some mechanistic investigations were undertaken to understand the nature of the active in situ generated Pd-H catalyst. These studies revealed that the catalytic system is highly dependent on the large steric demand of the P(tBu)3 ligand. The use of an alternative ligand, cataCXium PinCy, also proved effective for generating an active catalyst, and it was demonstrated in some cases to display better selectivity for the one-carbon shifts of terminal olefins. A possible intermediate involved in the preparation of the active catalyst was characterized by its single-crystal X-ray structure, which revealed a monomeric tricoordinated palladium(II) acyl complex, bearing a chloride ligand.

High regioselectivity for allylic substitution of the cyclopentenyl picolinate 5 with benzylcopper reagent was attained with ZnBr2, and the finding was applied to the p-BrC6H4CH2 reagent. The cyclopentene moiety in the product was reduced to the cyclopentane, and the p-BrC6H4 was converted to the "Cu"C6H4 for the second allylic substitution with picolinate 8 to furnish the title compound after oxidative cleavage of the resulting olefin moiety.

(Chemical Equation Presented) A facile and efficient synthesis of pyrroles from readily available amino acids is described. The key step in the method is an aza-Wacker oxidative cyclization catalyzed by palladium(II)/Cu(OTf) 2. A series of pyrroles were obtained by this method under mild conditions.

Synthetic work toward the total synthesis of nitiol has culminated in the construction of two epimeric hydroxylated derivatives, the 1,22- dihydroxynitianes. Key stereodefining steps in the construction of the A-ring fragment (13) were the use of a siloxy-epoxide rearrangement reaction, a Pauson-Khand reaction, a Norrish 1 photochemical cleavage reaction, and a highly regio- and stereoselective hydrostannylation reaction of an ynoate. The stereochemistry of the synthetically challenging C-ring fragment (20) was established using an Ireland-Claisen reaction and a Grubbs ring-closing metathesis process as key steps. The 12-membered B-ring of the nitiane skeleton was constructed using a copper-promoted Stille cross-coupling and a Kishi-Hiyama-Nozaki carbonyl addition reaction. Unfortunately, the carbonyl addition reaction produced hydroxyl functionality that could not be selectively removed. Consequently, a synthesis of epimeric 1,22-dihydroxynitianes, which are compounds that are structural hybrids of two natural products, nitiol and variculanol, was completed.

Described is the asymmetric synthesis of the allylic alcohols 11 (85% ee), 15 (99% ee), 17 (93% ee), 19 (61% ee), and 21 (69% ee) through a Pd-catalyzed reaction of the unsymmetrical carbonates rac-10, rac-12, rac-14, rac-16, rac-18, and rac-20, respectively, with KHCO3 and H2O in the presence of bisphosphane 6. Similarly the allylic alcohols 23 (99% ee) and 25 (97% ee) have been obtained from the symmetrical carbonates rac-22 and rac-24, respectively. Reaction of the meso-biscarbonate 26 with H2O and Pd(0)/6 afforded alcohol 27 (96% ee), which was converted to the PG building block 32. The unsaturated bisphosphane 33 showed in the synthesis of alcohols 36, 37, and 39 a similar high selectivity as 6. The formation of alcohols 11, 15, and 17 involves an efficient dynamic kinetic resolution.

As an efficient alcohol protecting group, picolinates (Pic), prepared from the corresponding alcohols using commercial picolinoyl chloride, are readily cleaved by Zn(OAc)2 or Cu(OAc)2, even in the presence of other common alcohol protecting groups. Moreover, the picolinyl group at C-2 position in carbohydrates can be selectively cleaved to give methyl 4,6-O-benzylidene-3-O-picolinyl-α-d-glucopyranoside and 3-O-picolinyl methyl-4,6-O-benzylidene-α-d-galactopyranoside in good yields.

The liquid-phase reduction of α,β-unsaturated ketones [trans,4-phenyl,3-buten,2-one (benzalacetone C6H5CHCHCOCH3), 4 -methyl,3-penten,2-one (CH3) 2CCHCOCH3, and 3-penten,2-one CH3CHCHCOCH 3] to the corresponding α,β-unsaturated alcohols has been investigated on gold-supported catalysts. Au/Fe2O3 and Au/Al2O3 have been prepared by coprecipitation and deposition-precipitation. The catalytic behavior of a Au/Fe2O 3 "reference" catalyst supplied by the World Gold Council has been also investigated. In the hydrogenation of benzalacetone and 4-methyl,3-penten,2-one on the "homemade" Au/Fe2O 3 catalysts the unsaturated alcohol is the main reaction product. Chemoselectivity higher than 60% was achieved. On Au/Al2O 3, the selectivity is 10%. It is noteworthy that within the gold supported on iron oxide samples, the reference catalyst shows the lowest selectivity toward the formation of the unsaturated alcohol. In the hydrogenation of 3-penten,-2-one on the homemade Au/Fe2O 3, the saturated ketone is the main reaction product and the selectivity toward the formation of the unsaturated alcohol is 15% at conversion 90%. It is likely that the absence of bulky substituents on the conjugated CC double bond favors its adsorption on the catalytic sites, leading to the formation of the saturated carbonyl compounds as the main reaction product. A detailed characterization of the investigated catalysts by TEM and XRD is also reported.

(Chemical Equation Presented) The first example of a kinetic resolution process promoted by electrophilic selenium reagents is reported. Racemic allylic alcohols react with half equivalents of a selenenylating agent in methanol leading to the regiospecific formation of the corresponding addition products with a very high level of facial selectivity (from 95:5 to 98:2 dr). The unreacted alcohols can be recovered in an optically enriched form (from 90 to 94% ee).

A new route is outlined for preparation of vinyl 1,2-diketones via a three-step sequence. First, allylic alcohols are photooxidized by 1O2 to hydroperoxides, which are reduced to vinyl 1,2-diols. These vinyl 1,2-diols are oxidized to vinyl 1,2-diketones with oxoammonium salts, which are prepared in situ from organic nitroxyl radicals. The new route is short, avoids the use of protecting groups, and is generally applicable to obtain aliphatic or aromatic vinyl 1,2-diketones.

Whole lyophilised cells of Rhodococcus ruber DSM 44541 were employed for the oxidative kinetic resolution of sec-alcohols using acetone as hydrogen acceptor. The enantioselectivity of this process could be controlled effectively by introducing C-C multiple bonds into substrates, which were inefficiently recognised, in particular short-chain (ω-1)-alcohols and (ω-2)-analogs. Thus, the enantioselectivities of rac-2-pentanol (E=16.8) and rac-3-octanol (E=13.3) were significantly improved by introducing a C=C bond adjacent to the alcohol moiety to give racemic (E)-pent-3-en-2-ol and 4-(E)-octen-3-ol, which were resolved with excellent selectivities (E >100 and 50, respectively). In addition, it was found that high stereodifferentiation between the E- and Z-configured double bonds occurred, as the corresponding (Z)-isomers were not converted. Similar selectivity-enhancing effects were observed with acetylenic analogs.

The palladium-catalyzed deracemization of racemic cyclic and acyclic allylic methyl carbonates in water in the presence of N,N′-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphophino)benzamide] proceeds with high enantioselectivities to give the corresponding allylic alcohols in high yields. This deracemization involves a palladium-catalyzed allylic substitution with the in-situ-formed hydrogen carbonate ion and an irreversible decomposition of the intermediate allylic hydrogen carbonates, with formation of the corresponding allylic alcohols. The palladium-catalyzed reaction of racemic cyclic allylic acetates with potassium hydrogen carbonate in water in the presence of the chiral bisphosphane proceeds with a highly selective kinetic resolution to give the corresponding allylic alcohols and allylic acetates. Copyright

Equilibrium constants (Kde) are reported for the dehydration of hydrates of benzene, naphthalene, phenanthrene, and anthracene. Free energies of formation of the hydrates (ΔG°f(aq)) are derived by combining free energies of formation of the parent (dihydroaromatic) hydrocarbon with estimates of the increment in free energy (ΔGOH) accompanying replacement of a hydrogen atom of the hydrocarbon by a hydroxyl group. Combining these in turn with free energies of formation of H2O and of the aromatic hydrocarbon products furnishes the desired equilibrium constants, The method depends on the availability of thermodynamic data (i) for the hydrocarbons from which the hydrates are derived by hydroxyl substitution and (ii) for a sufficient range of alcohols to assess the structural dependence of ΔGOH. The data comprise chiefly heats of formation and standard entropies in the gas phase and free energies of transfer from the gas phase to aqueous solution (the latter being derived from vapor pressures and solubilities). They also include experimental measurements of equilibrium constants for dehydration of alcohols, especially cyclic, allylic, and benzylic alcohols. In general ΔGOH depends on whether the alcohol is (a) primary, secondary, or tertiary; (b) allylic or benzylic; and (c) open chain or cyclic. Differences in geminal interactions of the hydroxyl group of the alcohol with α-alkyl and vinyl or phenyl groups account for variations in ΔGOH of 5 kcal mol-1. Weaker variations which arise from β-vinyl/OH or β-phenyl/OH interactions present in the aromatic hydrates but not in experimentally studied analogues are estimated as 1.0 kcal mol-1. Equilibrium constants for dehydration may be expressed as their negative logs (pKde). Reactions yielding the following aliphatic, aromatic, and antiaromatic unsaturated products then have pKde values: +4.8, ethene; +15.0, ethyne; +22.1, cyclopropene; +28.4 cyclobutadiene; -22.2, benzene; -14.6, naphthalene; -9.2, phenanthrene; -7.4, anthracene. Large positive values are associated with formation of strained or antiaromatic double bonds and large negative values with aromatic double bonds. Trends in pKde parallel those of heats of hydrogenation. The results illustrate the usefulness of a substituent treatment for extending the range of currently available free energies of formation. In addition to hydroxyl substituent effects, ΔGOH, values of ΔGπ for substitution of a π-bond in a hydrocarbon are reported.

Succinoylamino hydroxyethylamino sulfonyl urea derivatives of the formula: wherein the substituents are as defined in the specification, are effective as retroviral protease inhibitors, and in particular as inhibitors of HIV protease.

A cryptophycin compound is provided having the structure: Further provided are methods of producing cryptophycins by total synthesis and methods of using cryptophycins in pharmaceuticals. It is a further object of this invention to use cryptophycins to inhibit the proliferation of mammalian cells. Moreover, methods of using cryptophycins to treat neoplasia is also provided.

The synthesis of unit A of the cryptophycins from (S)-trans-3-penten-2- ol and from (S)-trans-4-hexen-3-ol has been completed. The key stereodetermining step is a [2,3]-Wittig rearrangement of a propargyl ether. Elaboration of the rearrangement product was accomplished by means of a selective hydroboration-oxidation of a terminal alkyne, Horner-Emmons homologation of the derived aldehyde, followed by selective ozonolytic cleavage and Wittig olefination. This synthesis provides easy access to the series of cryptophycin analogues that incorporate a modified aromatic ring in unit A.

At high [Cl ] (> 2.0 M), PdCl42- catalyzes the exchange of chiral allylic alcohols with hydroxy, methoxy, and phenyl to give chiral allyl-substituted olefins. With unsymmetrical olefins, isomerization occurs along with exchange. The hydroxyl exchange occurs in aqueous solution while the other exchanges are carried out in methanol solution. At low [Cl-] (0.1 M) oxidation to the corresponding β-hydroxy-, methoxy-, and phenyl-substituted carbonyl compounds occurred. The absolute configurations of the oxidation and exchange products should be the same if the same mode of addition to the Pd(II)-β-complex is operative. The absolute configurations of the oxidation and exchange products for the phenylation reaction were the same, while for hydroxy and methoxy they were different. This result indicates methanol and water must have different stereochemistries of addition at high and low [Cl-]. Thus, previous studies showing anti hydroxypalladation at high [Cl-] are not valid indicators of the stereochemistry at low [Cl-]. If anti addition occurs at high [Cl-], the addition must be syn at low [Cl-].

Piperylene hydration in the presence of KU-23 cation exchanger was studied at 95 and 105°C. The following main products of the reaction were identified using GLC and independent synthesis: 3-penten-2-ol; unsaturated C10 alcohols (6-methyl-3,7-nonadien-2-ol and 6-methyl-2,7-nonadien-4-ol); and linear and cyclic piperylene dimers, trimers, and tetramers. The effect of certain factors such as molar excess of water, catalyst concentration, and process duration on the reaction was examined. Formation rate curves of the products were taken Linear piperylene oligomers were found to dominate in the reaction mixture. Concentrations of unsaturated C10 alcohols and 3-penten-2-ol in the hydrocarbon phase were no higher than 4.5 and 1.5 mass %, respectively. A scheme of piperylene transformations in the course of the reaction was considered.

Rate constants and products for solvolyses of chlorodiphenylmethane (Ph2CHCl) and p-methoxybenzyl chloride in 2,2,2-trifluoroethanol (TFE)/water and TFE/ethanol are reported, along with additional kinetic data for solvolyses of tert-butyl and other alkyl halides (RX) in 97% w/w TFE/water and in 97% w/w hexafluoropropan-2-ol/water (HFIP). Results are discussed in terms of the solvent ionizing power (Y) and the solvent nucleophilicity (N), and contributions from other solvation effects are considered. Comparisons with other SN1 solvolyses show that solvolyses of Ph2CHCl in TFE mixtures are unexpectedly fast, but product ratios are unexceptional. An additional solvation effect influences solvolyses leading to delocalized cations, and a delocalized cationic transition state for concerted elimination may explain the recent results of Takeuchi et al., (J. Org. Chem. 1997, 62, 4904) without the need to postulate additional specific solvation effects for adamantyl systems, such as Bronsted-base solvation of α- and β-hydrogen atoms; concerted elimination may occur because simple tertiary alkyl cations are too unstable to form in predominantly aqueous media. Iodide/bromide and bromide/chloride rate ratios are very similar for 1-adamantyl halides and corresponding solvolyses of tert-butyl halides; these ratios decrease in the order aq EtOH > TFE > HFIP, as expected for an electrophilic solvation effect (this effect can readily be incorporated into Y values). From kinetic data for a series of tertiary alkyl chlorides in 97% TFE/water, it is shown that the susceptibility of rates of solvolyses of RCl to N decreases with an increase in steric hindrance or with an increase in charge stabilization. Also, the small kinetic solvent isotope effects for typical solvolyses (e.g., methyl tosylate) indicate that nucleophilic attack lags behind heterolysis of the C-X bond.

Unimolecular and collision induced fragmentations of cis- and trans-1-acetyl-2-methylcyclopropanes, complexed to bare Fe+ cations, were examined by means of tandem mass spectrometry. Stereoselective isotopic labeling data as well as comparative studies with acylic isomers reveal that two reaction pathways are in competition with each other. On the one hand, dehydrogenation, loss of ethene, and loss of acetaldehyde proceed via a common intermediate which is formed via ring cleavage of 1-acetyl-2-methylcyclopropane/Fe+ to yield the corresponding 3-hexen-2-one/Fe+ complexes; these undergo subsequently CH- and CC-bond activation via the remote functionalization mechanism. These ring cleavages are associated with a complete loss of stereochemical features for the cis and trans isomers. In contrast, unimolecular decarbonylation occurs stereoselectively and is favored for the trans isomers; this is rationalized via a stereoselective formation of cis- and trans-η3-allyl complexes in the course of the electrocyclic ring-opening process. Furthermore, interconversion reactions, thermodynamic and kinetic aspects, and isotope effects of the CH- and CC-bond activation processes are discussed.

The Claisen rearrangement of precursors bearing a stereogenic centre adjacent to carbon 1 of the pericyclic nucleus has been investigated in the sulfur series.Dithioesters having a methyl and various alkyl or alkenyls groups on the β-carbon were deprotonated by LDA.The resulting enethiolates were allylated on sulfur to give S-allyl ketenedithioacetals.The thio-Claisen transposition of the latter compounds was achieved either at room temperature or at 101 deg C to afford good yield of allylated dithioesters.Diastereomeric selectivities up to 95:5 have been observed.These results have been explained by a steric effect and correlated to allylic strain values.

The effect of adjacent unsaturation on the enzyme-catalyzed kinetic resolution of secondary alcohols is studied for a series of allylic, homoallylic, propargylic, homopropargylic, and phenyl-substituted 2-alkanols, using porcine pancreatic lipase (PPL) in anhydrous Et2O.Excellent enantioselectivity (high E value) was observed for α-phenethyl alcohol (3), propargylic alcohols (8 and 11), and (E)-allylic alcohols (9 and 12), but (Z)-allylic alcohols (10 and 13) showed poor selectivity.Enantioselectivity was also low for both (E)- and (Z)-homoallylic alcohols (15 and 16), homopropargylic alcohol (14), 1-phenyl-2-propanol (6), and 4-phenyl- 2-butanol (7).The enhanced enantioselectivity observed for (E)-allylic alcohols was exploited in the synthesis of the enantiomers of both components of the aggregation pheromone of the lesser grain borer, Rhyzopertha dominica (F.).The magnitude of the enantiomeric ratio (E value) can be dramatically affected by the accuracy of the values of ees and eep used in the calculation, especially when E is large.Variation in the value of E with the optical purity of the chiral derivatizing agent used to determine ees and eep is illustrated.

Primary and secondary allylic acetates and benzoates react with the dimethyl(phenyl)silyl-cuprate reagent to give allylsilanes, provided that the THF in which the cuprate is prepared is diluted with ether before addition of the allylic ester.The reaction is reasonably regioselective in some cases: (i) when the allylic system is more-substituted at one end than the other, as in the reactions 4->5 and 9->10; (ii) when the steric hindrance at one end is neopentyl-like, as in the reactions 15->16; and (iii) when the disubstituted double bond has the Z configuration, as in th e reactions Z-19->E-21 or, better, because the silyl group is becoming attached to the less-sterically hindered end of the allylic system, Z-20->E-22.The regioselectivity is better if a phenyl carbamate is used in place of the ester, and a three-step protocol assembling the mixed cuprate on the leaving group is used, as in the reactions 23->24 and E- or Z-29->E-21, or, best of all, because the silyl group is again becoming attached to the less-sterically hindered end of the allylic system, E- or Z-30->E-22.This sequence works well to move the silyl group onto the more substituted end of an allyl system, but only when the move is from a secondary allylic carbamate to a tertiary allylsilane, as in the reaction 38->39.Allyl(trimethyl)silanes can be made using alkyl- or aryl-cuprates on trimethylsilyl-containing allylic esters and carbamates, as in the reactions 40->41, and 43->44.The reaction of the silyl-cuprate with allylic esters and the three-step sequence with the allylic carbamates are stereochemically complementary, the former being stereospecifically anti and the latter stereospecifically syn.Homochiral allylsilanes can be ma de by these methods with high levels of stereospecificity, as shown by the synthesis of the allylsilanes 54, 58 and 59.

By the reaction with three N,N-dialkylamidosulfenyl chlorides 2 bearing representative sizes for the R groups on the nitrogen atom, several substituted secondary E or Z allylic alcohols (1a-h) have been converted into the corresponding pairs of diastereoisomeric allylic sulfinamides (3+-3′a-v), whose ratios have been determined by 1H NMR spectroscopy. Five cases of entirely diastereoselective [2,3]-sigmatropic rearrangement have been observed. The stereochemistry of one pure diastereoisomer 3′m has been determined by single crystal X-Ray analysis. When treated with 4-morpholinesulfenyl chloride, cyclohex-2-en-1-ol is stereoselectively converted to one diastereoisomer of the sulfinamide 5b which, by unambiguous procedures, led to the sane p.tolylsulfoxide 5a already obtained by treatment of cyclohex-2-en-1-ol with toluene-p-sulfenyl chloride.

Diastereoselective and regioselective transformations of cycloadducts to enantiomerically pure cyclopentadienes are reported.Retro-Diels-Alder processes finally give rise to pure enantiomers in high yield.

Aldehydes and ketones of the general formula I STR1 where R1 is hydrogen or an organic radical of 1 to n carbon atoms and R2 is a non-aromatic organic radical of 1 to m carbon atoms, (m+n) ranging from 2 to 24 and R1 and R2 being combinable to form a 4- to 12-membered ring, are prepared in a continuous manner by oxidizing an alcohol of the general formula II STR2 with oxygen or an oxygen-containing gas at elevated temperatures in the gas phase in the presence of a catalyst, by effecting the oxidation by means of a supported catalyst composed of an inert carrier having a smooth surface and from 0.1 to 20% by weight, based on the amount of carrier, of an active layer of copper, silver and/or gold in a tubular reactor or tube bundle reactor where the internal diameter D of the tube or tubes ranges from 10 to 50 mm and the largest diameter d of the coated supported catalysts is subject to the relationship d=from 0.1 to 0.2 D.

Chiral ferrocenylphosphine ligands, represented by (R)-N-methyl-N--1-ethylamine ((R)-(S)-1a), which have a pendant side chain bearing a hydroxy group at the terminal position, were designed and used successfully for palladium-catalyzed asymmetric allylic amination of allylic substrates containing a 1,3-disubstituted propenyl structure (RCH=CHCH(X)R: R = Ph, Me, n-Pr, i-Pr; X = OCOOEt, OCOMe, OP(O)Ph2, etc.).Reaction of the allylic substrates with benzylamine in the presence of a palladium catalyst prepared in situ from Pd2(dba)3 and (R)-(S)-1a gave high yields of amination products (RCH=CHC*H(NHCH2Ph)R: >97percent ee (R) for R = Ph, 73percent ee (S) for R = Me, 82percent ee (S) for R = n-Pr, and 97percent ee (S) for R = i-Pr).The allylamines were converted into optically active amino acids and their derivatives.The high stereoselectivity of the ferrocenylphosphine ligand is expected to be caused by an attractive interaction between the terminal hydroxy group on the ligand and the incoming amine, which directs the nucleophilic attack on one of the ?-allyl carbons.The key role of the hydroxy group was supported by an X-ray structure analysis of a ?-allylpalladium complex and (31)P NMR studies.It was demonstrated that the pendant side chain on the ferrocenylphosphine ligand is directed toward the reaction site on palladium and the terminal hydroxy group is located at the position close to one of the ?-allyl carbon atoms and that ?-allyl group on the palladium coordinated with the ferrocenylphosphine 1a adopts one of the two possible conformational isomers with high selectivity (20/1) in an equilibrium state.

Potassium triphenylborohydride is an excellent 1,4-reducing agent for acyclic enones and β-unsubstituted cyclohexenones, and shows a greater tendency for 1,4-reduction than K-Selectride for β-substituted cyclohexenones and aromatic enones.

Group IVA metallocene complexes such as bis(η5-cyclopentadienyl)zirconium dihydrides, Cp2ZrH2 (1), and hafnium dihydrides, Cp2HfH2 (8), catalyze the chemoselective reduction of polycarbonyl compounds to hydroxy carbonyl compounds.For instance, the reduction of keto aldehydes 3-ketobutanal (2g) and 2-phenyl-2-ketoethanal (2h) proceeded selectively at aldehyde group to provide the corresponding hydroxy ketones 3g and 3h in 91percent and 93percent yields, respectively.Under similar conditions, however, cyclohexanediones were easily aromatized to benzenediols.On the other hand, 1 and 8 also catalyze the selective 1,2-reduction of various types of α,β-unsaturated carbonyl compounds, giving the corresponding allylic alcohols in good to excellent yields.Thus, steroidal dicarbonyl compounds, having an enone framework in their molecules Δ4-androstene-3,17-dione (11a) and Δ4-progestene-3,20-dione (11b) were reduced by 1 to 17-hydroxy-Δ4-androsten-3-one (12a) and 20-hydroxy-Δ4-progest-3-one (12b), which are essential human hormones, in 80percent and 67percent yields, respectively.

Chiral allylic β-hydroxysulfoxides 2 have been hydroxylated by the osmium tetroxide catalyzed reaction.The reaction can be highly stereoselective depending on the nature of the substituent linked to the double bond and the configurations of the sulfoxide and hydroxylic groups.The diastereoselectivity can be as high as 90 percent.This methodology was applied to the asymmetric synthesis of L-arabinitol.

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The transformations of unsaturated alcohols (2-hexen-3-ol, 1-penten-4-ol, 1-penten-4-ol and 2-methylenecyclohexanol) were studied under identical experimental conditions in the presence of various Rh and Ru complexes (RhCl(PPh3)3, RhH(PPh3)4, RhCl3*3H2O, RhCl3*3H2O + PPh3, Rh(COD)Cl2, Rh(COD)Cl2 + PPh3, RhCl2(PPh3)3 and RuH2(PPh3)4).Several aspects of both the unsaturated alcohol and the complex exertconsiderable effects on the extent of the main reactions; isomerization to ketone and double-bond migration.

The selective reducing characteristics of sodium borohydride in a mixed tetrahydrofuran-methanol solvent system toward α,β-unsaturated ketones were investigated; allylic alcohols are procuced in good yield under mild conditions.

Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH4)2*1.5DMF.Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature.Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH4- unit is utilized and not four.Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and α,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones.It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones.An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.

Optically active threo-(2S,4S)-4-mercapto-2-pentanol, eryhtro-(2R,4S)-4-mercapto-2-pentanol and threo-(2S,4S)-pentanedithiol, were prepared from threo-(2R,4R)-pentanediol.The mechanism of thier formation discussed.The molecular optical rotation D of these compounds, of trans-(4S,6S)-, cis-(4S,6R)-dimethyl-1,3-oxathiane and of trans-(4S,6S)-dimethyl-1,3-dithiane, was determined and was related to the composition of the conformational mixture using Brewster's conformational rotatory power model.A complete conformational analysis of the six 2-(X)-4(Y)-substituted pentanes (X, Y = OH, SH) was obtained from their 1H NMR spectra in combination with their chiroptical properties.The threo compounds favour the aa conformation, whereas the ag-/g+a forms are preferred in the erythro isomers, expect for the 2,4-diols where the intramolecular hydrogen bonded form is predominant.

The effect of an "inside" allylic asymmetric center on the course of the intramolecular nitrile oxide cycloaddition reaction has been studied.

The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide (1/16 mol) were studied.Relationships were found between the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism.The ether formation observed with certain alcohols proceeds via a carbenium cation.The reaction conditions applied were found suitable for including water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination).From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield.Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism.The effect of DMSO is excerted directly, and proton-catalysis occurs simultaneously.