Josep Castells

Oxidative benzoin reactions

Abstract A one-pot synthesis (yields over 50%) of methyl and ethyl esters from aldehydes (and the corresponding alcohol), using aromatic nitrocompounds as oxidizing agents under the catalytic action of cyanide ion or of a conjugate base of a thiazolium ion, is described. A variety of by-products (α-hydroxybenzylidenaniline) ( 16 ), α-methoxybenzylidenaniline ( 21 ), α-cyanobenzylidenaniline ( 27 ), N 1 -hydroxy-N 1 ,N 2 -diphenylbenzamidine ( 28 ), and others) have been identified.

The formoin reaction

Abstract The formoin reaction, i.e. , the autocondensation of formaldehyde in an aprotic solvent catalysed by the conjugate base of a thiazolium ion, has been studied in detail. Glucose, galactose, dihydroxyacetone dimer, xylose, and arabinose have been identified as products. The influence of catalysts, temperature, basicity, and reaction time is documented. N , N -Dimethylformamide is a more convenient solvent than ether, benzene, or diglyme. Ethyldi-isopropylamine affords better yields of carbohydrate material thant riethylamine. At ≤60°, aldol condensations are reduced to a minimum. After 1–2 h of reaction (depending on the conditions), the yields begin to decrease and become zero after ∼24 h.

Synthetic applications of 2-(1,3-Dithian-2-yl)indoles V.1 asymmetric synthesis of dasycarpidone-type indole alkaloids

Chiral tetracyclic dasycarpidone-type compounds (αR, 1S, 5R)-4 and (αR, 1R, 5S)-16 have been synthesized from 2-(1,3-dithian-2-yl)indole 6 and (αR)-N-(β-hydroxy-α-phenylethyl)-Δ3-piperidein-2-one8 in three steps, following the methodology that we described recently.

Synthetic applications of 2-(1,3-dithian-2-yl)indoles. IV: New synthesis of the tetracyclic ABED ring system of Strychnos alkaloids

Abstract A new and versatile synthesis of tetracyclic compounds 10, 22 and 24 presenting the ABED ring system of Strychnos alkaloids is described by closure of the C1C11b bond in the key step. The intermediate tetrahydropyridinium salts 2 have been obtained from 2-(1,3-dithian-2-yl)indole (3) and either 2-cyano-3-ethyl-1-methyl-1,2,3,6-tetrahydropyridine (4a) or N-substituted Δ3-piperidein-2-ones (5).

New evidence supporting bis(thiazolin-2-ylidene)s as the actual catalytic species in the benzoin condensation.

Abstract Polymethylene-bridged (n= 2-8) thiazolium and benzothiazolium salts (plus bases) are used as catalysts for the benzoin condensation and it is found that catalytic activity depends strongly on the methylene bridge length. This result supports a previous postulation that bis (thiazolin-2-ylidene)s, and not thiazolin-2-ylidenes, are the catalytic species in the benzoin condensation catalyzed by thiazolium salts plus base.

Synthesis and reactivity of 2-(1,3-dithian-2-yl)indoles. III: Influence of the indole protective N-phenylsulfonyl group

Formation of the anion of 2-(1,3-dithian-2-yl)indoles was shown to be possible when the indole nitrogen is protected by a p-methoxyphenylsulfonyl group

1-ALKOXYCARBONYLALKYLIDENETRIPHENYLARSORANES : PREPARATION AND REACTIONS

Abstract The higher homologues of the well-studied alkoxycarbonylmethylenetriphenylarsonium ylide (3, R=H) can be easily obtained through the sequence: a), preparation of alkyl 2-triloxyalkanoates (1); b), reaction between these trifloxyderivatives and triphenylphosphine to give 1-alkoxycarbonylalkyltriphenylarsonium triflates (2); and c), basic treatment of the triphenylarsonium triflates (2) with alumina-supported potassium fluoride to give 1-alkoxycarbonylalkyledenetriphenylarsonium ylides (3). These higher homologues of (3, R=H) react with aromatic aldehydes in good to excellent yields, and give rise to synthetically interesting “coupling” and cyclopropanation reactions.

8-aryl-2-azabicyclo[3.3.1]nonan-7-ones. Synthesis and retro-michael ring opening

Abstract The synthesis of 8-aryl-2-azabicyclo[3.3.1]nonan-7-ones ( 7 ) by acid cyclization of 4-(3-aryl-2-oxopropyl)-2-piperidinecarbonitriles ( 5 ) is reported. Bicyclic α-aril-β-amino ketones 7 easily undergo a retro-Michael ring opening to give the corresponding 2-arylcyclohexenones 8 .

Synthesis and reactivity of 2-(1,3-dithian-2-yl)indoles. IV. Influence of the N,N-diethylcarbamoyl indole protecting group

Abstract The effect of the N.N-diethylcarbamoyl indole protecting group on the reactivity of 2-(1,3-dithian-2-yl)indole 7 in front of a series of electrophiles, as well as the potential synthetic usefulness of the resulting 2,2-disubstituted dithianes is reported.

Synthesis of chiral 2-aryl-4-piperidones

The synthesis of chiral 2-(2-indolyl)- and 2-(3-indolyl)-4-piperidones by reaction of N,N-dimethyl-4-oxo-2-[1-(phenylsulfonyl)-indolyl] piperidinium iodide and (R)-(-)-phenylglycinol is reported