Search results for "Rearrangement"

Asymmetric Tandem Reactions: New Strategies and Applications

2013

Abstract The application of allylic sulphoxides and, particularly, the chiral amine reagent tert-butanesulphinamide has been extended to three different tandem processes. The condensation of (R)-(+)-allyl p-tolyl sulphoxide, fluorinated nitriles and alkyl propiolates led to a new family of enantiomerically pure fluorine-containing 1,4- dihydropyridines. A diastereoselective nucleophilic addition of fluorinated nucleophiles onto (R)-(tert-butanesulphinyl) imines, followed by an intramolecular aza-Michael reaction gave rise to either fluorinated isoindolines or 3-substituted indanones in a stereoselective manner.

Anaerobic Palladium-Catalyzed Chemoselective Oxidation of Allylic and Benzylic Alcohols with α-Bromo Sulfoxide as a Co-Oxidant.

2007

A chemoselective palladium-catalyzed anaerobic oxidation of allylic and benzylic alcohols using an α-bromo sulfoxide as a co-oxidant is described for the first time. The catalyst system is simple and has a long life because of the allowance of phosphane ligands under the non-aerobic conditions. The advantages of the described method include no overoxidation of primary alcohols to carboxylic acids because of the mild conditions applied, the tolerance of oxygen-sensitive functionalities such as a carbon-carbon double bond, an organothio group, or a diorganoamino group and the effective preparation of α,β-unsaturated aldehydes and ketones, resulting from the oxidation of primary and secondary …

A Novel Allylic Anchor for Solid-Phase Synthesis—Synthesis of Protected and Unprotected O-Glycosylated Mucin-Type Glycopeptides

1995

HYCRON, an Allylic Anchor for High-Efficiency Solid Phase Synthesis of Protected Peptides and Glycopeptides

1997

The recently developed allylic HYCRON anchor1 exhibits excellent properties for the solid phase synthesis of protected peptides and glycopeptides. Model reactions with analogous low molecular weight compounds assessed the acid- and base-stability of the polar and flexible HYCRON linkage. The new anchor is available in a two-step synthesis and allows the use of both the Boc- and the Fmoc-strategy, which can even be combined within one synthesis. Protected glycopeptides are released under almost neutral conditions, taking advantage of the Pd(0)-catalyzed allyl transfer to a weakly basic nucleophile such as N-methylaniline. The highly efficient synthesis of O-αGalNAc(TN)-peptides of the MUC-1 …

ChemInform Abstract: Diastereoselective Intramolecular Additions of Allyl- and Propargylsilanes to Iminium Ions: Synthesis of Cyclic and Bicyclic Qua…

2010

Cyclization of the chiral imino lactones with allylic or propargylic groups required acidic conditions to afford spirocyclic (II) or (XII).

Synthesis of Spirovetivane Sesquiterpenes from Santonin. Synthesis of (+)-Anhydro-?-rotunol and All Diastereomers of 6,11-Spirovetivadiene.

2005

The synthesis of the spirovetivane sesquiterpenes (+)-anhydro-beta-rotunol and all the diastereomers of 6,11-spirovetivadiene in enantiomerically pure form has been achieved starting from santonin. The key step is the silicon-guided acid-promoted rearrangement of a 1-trimethylsilyl-4,5-epoxyeudesmane prepared from santonin in several steps involving lactone reductive opening, conjugate addition of TMSLi-CuCN, deoxygenation of a carbonyl group, and epoxidation. Rearrangement of the epoxide gave a spiro[4,5]decanediol which was used as a synthetic intermediate. From this compound, (+)-anhydro-beta-rotunol was prepared after elimination of the primary hydroxyl group in the side chain, followed…

Photochemical versus aluminium chloride-catalyzed fries rearrangement of aryl hydrogen succinates. synthesis of 2(3H)-furanones

1989

The photochemical and aluminium chloride-catalyzed Fries rearrangement of a series of aryl hydrogen succinates3 a–f to the corresponding 4-oxoacids1 a–f are compared. Both approaches are complementary: the photochemical process is more general and becomes the method of choice for the succinoylation of phenols supporting alkoxy or hydroxy substituents, while the classical rearrangement is superior in the presence of alkyl or halogen substituents. These results are applied to the preparation of the 2(3H)-furanones2 a–f.

ChemInform Abstract: A Novel Synthesis of Chain-Extended Amino Sugar Derivatives Through Aza-Cope Rearrangement of N-Galactosyl-N-homoallylamines.

2010

Abstract Chain-extended amino sugars are synthesized via stereocontrolled Lewis acid-catalyzed aza-Cope rearrangement of N-glycosyl homoallylamines in high yield and stereoselectivity.

A novel synthesis of chain-extended amino sugar derivatives through aza-Cope rearrangement of N-galactosyl-N-homoallylamines

1998

Abstract Chain-extended amino sugars are synthesized via stereocontrolled Lewis acid-catalyzed aza-Cope rearrangement of N-glycosyl homoallylamines in high yield and stereoselectivity.

ChemInform Abstract: Solution-, Solid-Phase, and Fluorous Synthesis of β,β-Difluorinated Cyclic Quaternary α-Amino Acid Derivatives: A Comparative St…

2008

The diastereoselective synthesis of cyclic β,β-difluorinated α-amino acid derivatives bearing a quaternary stereocenter is described. The process relies on the chemo- and diastereoselective addition of allylic organometallic reagents to fluorinated α-imino esters and a subsequent ring-closing metathesis reaction (RCM). Complete selectivity in the nucleophilic addition was achieved with (R)-phenylglycinol methyl ether as a chiral auxiliary. The resulting amino acids were introduced into peptide chains, which could facilitate the preparation of potentially bioactive dipeptide derivatives. In addition, the solution synthesis of these cyclic fluorinated α-amino acids was successfully adapted to…