Enantio- and diastereoselective, stereospecific mannich-type reactions in water

Catalytic asymmetric Mannich-type reactions in water proceeded in high yields and selectivities using a combination of ZnF2 and a chiral diamine that has the methoxy groups on the aromatic rings. In these reactions, either syn- or anti-Mannich adducts were stereospecifically obtained from (E)- or (Z)-silicon enolate, in contrast with most asymmetric Mannich-type reactions.     

Electrophilic aromatic substitution reactions of 1,2-dihydro-1,2-azaborines

The aromatic boron-nitrogen heterocycle 1,2-dihydro-1,2-azaborine undergoes classical electrophilic substitution. These reactions allow easy functionalization to provide a variety of 3- and 5-substituted derivatives. [reaction: see text].     

The synthesis of homoallylic amines utilizing a cuprate-based 1,2-metalate rearrangement.

Lithiation of the N-2,4,6-triisopropylbenzenesulfonyl-2-pyrroline (16) and treatment of the resulting cyclic vinyllithium reagent with R2CuCNLi2 produced an acyclic vinyl organometallic species that, when treated with an electrophile (H2O or RX), gave the homoallylic sulfonamides 18a-k in 37-93% yields and in > 95% diastereoselectivity. The deprotection of a representative homoallylic sulfonamide 18d was achieved in 83% yield by sonication in the presence of lithium wire and catalytic 4,4'-di-tert-butylbiphenyl (DBB). The efficacy of this general procedure for the production of homoallylic amine derivatives is demonstrated by the preparation of the diene amine 25, a key intermediate in the synthesis of a squalene synthetase inhibitor.     

Electrophilic fluorination of cationic Pt-aryl complexes

The electrophilic fluorination of several (triphos)Pt-aryl(+) establishes the first example of aryl-F coupling from a Pt center.     

Synthesis of (+)-manoalide via a copper(I)-mediated 1,2-metalate rearrangement

An enantiospecific synthesis of the phospholipase A(2) inhibitor (+)-(4R)-manoalide is reported in which all 25 carbons of the sesterterpenoid skeleton are constructed from 3-furaldehyde, trimethylalane, oxirane, CO, beta-ionone, and propargyl bromide. The overall yield for the longest linear sequence (12 steps) is 12%. Key steps include (a) a zirconium-catalyzed carboalumination reaction to construct the C10-C11 trisubstituted alkene, (b) a Cu(I)-mediated 1,2-metalate rearrangement to construct the C6-C7 trisubstituted alkene, (c) a Sharpless kinetic resolution to secure the (4R)-stereochemistry, (d) generation of a 5-stannyl-2,3-dihydrofuran by Mo-catalyzed cycloisomerization of a homopropargylic alcohol, and (e) construction of the hydroxyfuranone ring by photooxidation of a silylfuran.     

Highly diastereoselective synthesis of propargylic 1,2-anti-diol derivatives using alpha-alkoxypropargylstannanes

Propargylic 1,2-anti-diol derivatives 2 and 10 are prepared in high yield and excellent diastereoselectivity by addition of alpha-alkoxypropargylstannanes 4a and 4b to aldehydes in the presence of BuSnCl(3). We also introduce the use of KF on Celite as a convenient and mild reagent for removal of the organotin waste products of these reactions. Reaction: see text.     

Verification of stereospecific dyotropic racemisation of enantiopure d and l-1,2-dibromo-1,2-diphenylethane in non-polar media

The first example of a dyotropic rearrangement of an enantiomerically pure, conformationally unconstrained, vicinal dibromide confirms theoretical predictions: d and l-1,2-dibromo-1,2-diphenylethane racemise stereospecifically in refluxing benzene without crossover to the meso-isomer. An orbital analysis of this six-electron pericyclic process is presented.     

A novel stereospecific synthesis of glycosyl cyanides from 1,2-O-sulfinyl derivatives

[reaction: see text] An efficient synthesis of 1,2-trans-glycosyl cyanides via 1,2-O-sulfinyl monosaccharides is described. Such S(N)2-type displacements at the anomeric center are stereospecific and are best performed with sodium cyanide in the presence of ytterbium triflate. Significantly, the resulting 1,2-trans-glycosyl cyanides have a free hydroxyl group at C-2 ready for further modification.     

Electrophilic oxidant produced in the photodeoxygenation of 1,2-benzodiphenylene sulfoxide.

We report that the photodeoxygenation of 1,2-benzodiphenylene sulfoxide, 1, generates an intermediate capable of oxidizing the solvent benzene to phenol. The reactivity of the intermediate was probed with various substrates (2-methylbutane, chloride ion, and para-substituted aryl sulfides). The intermediate produced in the sulfoxide photodeoxygenation displays an electrophilic oxidation chemistry. Our data on 1 contrast with the behavior of hydroxyl radical but resemble the chemistry observed for gas-phase atomic oxygen [O((3)P)] and for solution-phase photodeoxygenations of dibenzothiophene sulfoxide, 3, and pyridine N-oxide, 5. Correlations are made between the ionization potential of the acceptor molecules and the logarithm of the relative rate constants in order to advance the idea that the oxidizing agent of the title reaction may be solution-phase O((3)P).     

Highly diastereoselective generation of various 3,3-disubstituted allyl boronates for the stereospecific construction of quaternary centers

Single isomer trisubstituted olefins were converted into allyl boron nucleophiles that were condensed with aldehydes to give products containing quaternary centers. The products were obtained in extremely high diastereomeric ratios, a reflection of the stereochemical integrity of the starting materials.     

Rhodium-catalyzed diastereoselective 1,2-addition of arylboronic acids to chiral trifluoroethyl imine

Rhodium-catalyzed 1,2-addition of arylboronic acids 4a-j to chiral trifluoroethyl imine 3 afforded diastereomerically enriched sulfinamides 5a-j. The chiral auxiliary of the sulfinamide products was readily removed under acidic methanolysis to provide the corresponding trifluoroethylamine analogs 6a-j.     

Stereodivergent catalytic doubly diastereoselective nitroaldol reactions using heterobimetallic complexes

Stereodivergent construction of three contiguous stereocenters in catalytic doubly diastereoselective nitroaldol reactions of alpha-chiral aldehydes with nitroacetaldehyde dimethyl acetal using two types of heterobimetallic catalysts is described. A La-Li-BINOL (LLB) catalyst afforded anti,syn-nitroaldol products in >20:1-14:1 selectivity, and a Pd/La/Schiff base catalyst afforded complimentary syn,syn-nitroaldol products in 10:1-5:1 selectivity.     

A simplified procedure for the stereospecific transformation of 1,2-diols into epoxides

A simple, ‘one-pot’ procedure for the conversion of vicinal diols into epoxides via halohydrin ester intermediates has been developed. This method tolerates a wide range of functionality including acid sensitive functional groups. The transformation proceeds via a, usually highly regioselective, nucleophilic opening of a cyclic acetoxonium intermediate, generated from a cyclic orthoacetate and Me₃SiCl, acetyl bromide or acetyl chloride/NaI to form 1-acetoxy-2-chloride, 1-acetoxy-2-bromide or 1-acetoxy-2-iodide intermediates, respectively. No epimerization occurs, even with benzylic substrates. Subsequent base mediated methanolysis furnishes epoxides in excellent overall yield. Application of this method led to an efficient formal synthesis of the leukotriene antagonist SKF 104353, commencing with the highly enantioselective cis-dihydroxylation of methyl 3-[2-(8-phenyloctyl)phenyl]propenoate.     

Regio- and diastereoselective cyclization reactions of free and masked 1,3-dicarbonyl dianions with 1,2-dielectrophiles

Despite their simplicity and synthetic usefulness, cyclisation reactions of 1,3-dicarbonyl dianions with 1,2-dielectrophiles are problematic, since both dianions and 1,2-dielectrophiles are highly reactive compounds (low reactivity matching). In addition, 1,2-dielectrophiles are often rather labile, and reactions with nucleophiles can result in polymerisation, decomposition, formation of open-chained products, elimination or SET-reactions. These intrinsic limitations can be overcome by a proper reactivity tuning and by the use of electroneutral dianion equivalents (masked dianions) in Lewis acid catalysed reactions. The cyclisations reported herein allow for an efficient, regio- and stereoselective one-pot synthesis of biologically relevant ring systems.