Amine-catalyzed addition of azide ion to alpha,beta-unsaturated carbonyl compounds

[formula: see text] A new protocol for the beta-azidation of alpha,beta-unsaturated carbonyl compounds is described. The method employs tertiary amines as catalysts for azide addition. The azide source is a 1:1 mixture of TMSN3 and AcOH. Tertiary amines, either in solution or bound to a solid support, are efficient catalysts for the reaction.     

Enhanced pi ... pi interactions in alpha,beta-unsaturated carbonyls

High level ab initio calculations on complexes of benzene with acrolein and ethene reveal that pi ... pi interactions to electron deficient acrolein are remarkably similar to those found in the benzene dimer.     

Asymmetric 1,4-hydrosilylations of alpha,beta-unsaturated esters

Complexing catalytic amounts of CuH with a nonracemic JOSIPHOS or SEGPHOS ligand, together with stoichiometric PMHS, leads to exceedingly efficient and highly enantioselective 1,4-reductions of beta,beta-disubstituted enoates and lactones. An unprecedented substrate-to-ligand ratio of 7700:1 for this type of reaction is documented.     

Regiocontrolled, palladium-catalyzed bisfunctionalization of allenyl esters. Multicomponent coupling approaches to highly substituted alpha,beta-unsaturated delta-lactones

A palladium-catalyzed regioselective bisfunctionalization of allenyl esters with boronic acids (nucleophiles) and aldehydes (electrophiles) was demonstrated. The three-component coupling afforded alpha,beta-unsaturated delta-lactones under mild conditions and with excellent chemo-, regio-, and diastereoselectivity. Aromatic, heteroaromatic and vinylic boronic acids (R1B(OH)2) reacted with ethyl 2,3-butadienoate and benzaldehyde to afford the corresponding 4-R(1),6-Ph-disubstituted alpha,beta-unsaturated delta-lactones in 62-78% yields. Lactones derived from aromatic, heteroaromatic, and vinylic aldehydes were isolated in 51-58% yields, while aliphatic aldehydes were less reactive. The regiochemistry of bisfunctionalization of allenyl ester homologues remained controlled by the ester substituent, and the reactions afforded cis-4,5,6-trisubstituted alpha,beta-unsaturated delta-lactones and esters of (Z)-syn-3,4,5-trisubstituted-5-hydroxy-2-pentenoic acids in combined 47-65% yields. The superior performance of a pi-allylpalladium(II) dimer catalyst featuring an auxiliary allyl ligand derived from beta-pinene, among diverse palladium(II) catalysts, was demonstrated. A catalytic cycle involving an unsymmetrical bis-pi-allylpalladium complex as the key intermediate was proposed, and the communication highlights the synthetic potential of such intermediates. However, the efficiency of asymmetry transfer remained low (<20%).     

A titanium-catalyzed three-component coupling to generate alpha,beta-unsaturated beta-iminoamines

The three-component coupling of an amine, alkyne, and isonitrile is facilitated by a titanium complex bearing the N,N-di(pyrrolyl-alpha-methyl)-N-methylamine (dpma) ligand. From this methodology, alpha,beta-unsaturated beta-iminoamines are generated regioselectively with many substrates and are available on multigram scales.     

Palladium-catalyzed carbonylation of yne esters leading to gamma-alkylidene alpha,beta-unsaturated gamma-lactones

[reaction: see text] The reaction of yne esters with carbon monoxide (1 atm) in the presence of palladium complexes gives bicyclic unsaturated lactone derivatives in good to high yields. The 2-pyridinyloxy group is a good leaving group among leaving groups examined.     

The intramolecular,stereoselective addition of sulfoximine carbanions to alpha,beta-unsaturated esters

ortho-Bromocinnamates can be coupled with methyl phenylsulfoximine to afford N-arylsulfoximines in excellent yield. Treatment of these products with an amide base results in a completely stereoselective cyclization to afford enantiomerically pure benzothiazines. This reaction is stereospecific.     

Highly stereoselective intermolecular oxy-michael addition reaction to alpha,beta-unsaturated malonate esters

[reaction: see text] The highly diastereoselective oxy-Michael addition of the "naked" anion of (6S)-methyl delta lactol to alkylidiene-, arylidene-, and heteroarylidenemalonate derivatives leading to the direct formation of THP-protected beta-hydroxy ester derivatives is described. Subsequent acid-mediated deprotection affords the enantioenriched aldol products in quantitative yields.     

On the synthesis of Z-gamma-amino-alpha,beta-unsaturated esters via Ru-catalyzed coupling

[formula: see text] A synthesis of gamma-amino acids and their cyclic derivatives, 3-pyrrolinones, from alpha-amino acids employs a ruthenium-catalyzed Alder ene reaction as a key step in the sequence. Cyclopentadienylruthenium (1,4-cyclooctadiene) chloride catalyzes the addition of gamma-amido-alpha,beta-alkynoate esters with monosubstituted alkenes. The major product arises from C-C bond formation at the alpha-carbon of the alkynoate. The reaction exhibits high chemoselectivity. The ruthenium-catalyzed addition occurs in preference to a Diels-Alder reaction. The two new double bonds are created with complete geometrical control. The initial gamma-amido-alpha,beta-unsaturated ester can be cyclized to the pyrrolinones with a tin catalyst.     

Stereoselective enol tosylation: preparation of trisubstituted alpha,beta-unsaturated esters

[Reaction: see text] The stereoselective preparation of (E)- or (Z)-trisubstituted alpha,beta-unsaturated esters in three steps from N-protected glycine is presented. The key step in the synthesis is the highly selective enol tosylation of gamma-amino beta-keto esters. The enol tosylates are stable, crystalline compounds that undergo smooth and effective Suzuki-Miyaura coupling reaction with a variety of aryl boronic acids.     

Highly enantioselective epoxidation of alpha,beta-unsaturated esters by chiral dioxirane

This paper describes a highly enantioselective epoxidation of alpha,beta-unsaturated esters using the fructose-derived ketone 2 as catalyst and Oxone as oxidant. High ee's have been obtained for a number of trans and trisubstituted substrates (82-98% ee). The results described show that it is feasible for dioxiranes to effectively epoxidize electron-deficient olefins with high ee's.     

Calcium-catalyzed diastereo- and enantioselective 1,4-addition of glycine derivatives to alpha,beta-unsaturated esters

The first highly diastereo- and enantioselective catalytic asymmetric 1,4-addition reactions of a glycine Schiff base to beta-substituted alpha,beta-unsaturated esters have been developed. The reaction pathway was successfully controlled, and the desired 1,4-addition products were exclusively obtained with high enantioselectivities. The product obtained was converted to a 3-substituted glutamic acid derivative by acid hydrolysis.     

Kinetics and mechanism of the addition of nucleophiles to alpha,beta-unsaturated thiol esters

Compounds containing the UV-absorbing chromophores p-methoxycinnamate, p-methoxycinnamide, or anthranilate and an alpha,beta- or alpha,beta,gamma,delta-unsaturated thiol ester (crotonyl or sorboyl) have been prepared. These compounds are subject to nucleophilic attack at the C=C conjugated to the thiol ester carbonyl group. The kinetics of the reactions of these thiol esters with N-acetyl-l-cysteine (NAC), N-acetylcysteamine, and N(2)-acetyl-L-lysine (NAL) have been studied, and the thiol addition products have been identified. The reaction rates increased at higher pH, and the reaction of NAC thiolate with a crotonyl thiol ester in 1:1 (v/v) acetonitrile/aqueous HEPES exhibited buffer catalysis as a result of protonation of the enolate intermediate. At the same concentration, NAC underwent approximately 300-fold more reaction than NAL with a crotonyl thiol ester at pH 9.8. Additionally, a crotonyl thiol ester was found to be 7.9 times more reactive than a sorboyl thiol ester toward NAC addition. These unsaturated thiol esters may serve as a means of covalently binding UVA and UVB sunscreens to the outer layer of skin to provide long-lasting protection.     

Intramolecular Pauson-Khand reactions of alpha,beta-unsaturated esters and related electron-deficient olefins

The intramolecular Pauson-Khand (PK) reaction of a variety of electron-poor enynes having an ester, cyano, or phosphonate group at the olefin terminus is described. Depending on the reaction conditions and substitution at the enyne, their dicobalthexacarbonyl complexes led preferentially to the exocyclic 1,3-diene or to the PK cyclopentenone product. In general, the 1,3-diene was obtained as the major product under N-oxide-promoted conditions, while the PK product was selectively formed in refluxing acetonitrile.     

Catalytic asymmetric epoxidation of alpha,beta-unsaturated esters using an yttrium-biphenyldiol complex

We succeeded in a catalytic asymmetric epoxidation reaction of alpha,beta-unsaturated esters via a conjugate addition of an oxidant using 2-10 mol % of the yttirium-chiral biphenyldiol catalyst. A variety of substrates with beta-aryl and beta-alkyl substituents were epoxidized efficiently, yielding the corresponding alpha,beta-epoxy esters in up to 97% yield and 99% ee.     

Single-isomer tetrasubstituted olefins from regioselective and stereospecific palladium-catalyzed coupling of beta-chloro-alpha-iodo-alpha,beta-unsaturated esters

The efficient regioselective and stereospecific synthesis of tetrasubstituted olefins using a mild and convenient method is disclosed. 2-Alkynyl esters are selectively converted to E-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters by exposure to Bu4NI in refluxing dichloroethane. These products are produced cleanly, regio- and stereoselectively, and in high yields. Single-isomer tetrasubstituted olefins bearing four different carbon substituents are then synthesized by sequential palladium-catalyzed coupling reactions. Selectivity results from reactivity differences in the intermediate substrates.     

Contribution to the synthesis of chiral allenic esters

A phosphorus ylide bearing a 10-phenylsulfonylisoborneol unit reacted with ketenes, generated in situ from acid chlorides and triethylamine, to give allenic compounds. The reaction with methylketene led to asymmetric induction with the selective synthesis of an allene with axial chirality corresponding to an S configuration. The structure of the chiral allene 10-phenylsulfonylisobornyl penta-2,3-dienoate was determined by X-ray crystallography. Chirooptical studies of the chiral allene derivatives were done.