Addition of Lithium Anion of (Acetylmethylene)triphenylphosphorane to Nonracemic Sulfinimines: Total Synthesis of (+)-241D and Formal Total Synthesis of (+)-Preussin.

The addition of lithium anion of (acetylmethylene)triphenylphosphorane to nonracemic sulfinimines was investigated. It was found that the addition proceeded with good diastereoselectivity and further reaction of the formed sulfinimidophosphorane with several aldehydes afforded the ß-sulfinamido substituted enones in good yields. The resultant enones were elaborated to the synthesis of alkaloid (+)-241D, to the formal total synthesis of (+)-preussin, and to the synthesis of aminocyclopentenol.

Stereoselective Synthesis of ß-Amino Ynones by the Addition of Alkynones to Nonracemic Sulfinimines: Formal Total Synthesis of l-Xylo and l-Arabino Phytosphingosines.

The addition of silyl enol ethers obtained from ynones to sulfinimines furnished the corresponding ß-sulfinamido ynones in a very good yield and diastereoselectivity. The formed ynones serve as precursors amenable for the synthesis of bioactive compounds. This has been illustrated in the synthesis of l-xylo and l-arabino phytosphingosines.

Enantioselective Synthesis of ß-Allenoates via Phosphine-Catalyzed and ZnI2-Promoted Preparation of Oxazolidines and Propargylamines Using Chiral Amines, 1-Alkynes, and Propiolates.

Diphenylphosphinoethane (DPPE)-catalyzed and ZnI2-promoted in situ formation of oxazolidine, alkynyl zinc, and propargylamine intermediates from 1-alkynes, chiral (S)-diphenyl(pyrrolidin-2-yl)methanol, and propiolates gave the corresponding chiral (R)-ß-allenoates in 40-72% yield with up to >99% ee. The intermediate propargylamine was isolated in 50% yield and converted to give the ß-allenoate 10aa in 68% yield and 96% ee upon reaction with ZnI2. The results are discussed considering a mechanism involving oxazolidine and iminium ions formed in situ followed by addition of alkynyl zinc complex to produce the propargylamine that gives the corresponding allenoate via a 1,5-hydrogen shift in the presence of ZnI2.

Synthetic Transformations Using Molecular Oxygen-Doped Carbon Materials.

Carbon materials like activated carbon (AC) undergo chemisorption with O2 to give species with electron deficiency in the carbon skeleton and negative charge at the oxygen end that upon reaction with PPh3 and benzoic acid afford Ph3P═O. Whereas amine donors react with O2-chemisorbed AC and nucleophiles to give dehydrogenatively coupled products in 67-89% yields via the corresponding radical cation and iminium ion intermediates, the reactions using ß-naphthoxide derivatives give the corresponding oxidatively coupled bi-2-naphthol products in 68-95% yields.

Synthesis of ß-Amino-Substituted Enones by Addition of Substituted Methyl Enones to Sulfinimines: Application to the Total Synthesis of Alkaloids (+)-Lasubine II and (+)-241D and the Formal Total Synthesis of (-)-Lasubine I.

Addition of silyl enol ethers obtained from substituted methyl enones to chiral sulfinimines afforded the ß-amino-substituted enones with excellent selectivity. Utility of the obtained N-sulfinyl ß-amino ketones possessing α,ß-unsaturation is exemplified in the total synthesis of the quinolizidine alkaloid natural products (-)-lasubine I, (+)-lasubine II, and substituted piperidine alkaloid (+)-241-D.

Diastereoselective Synthesis of Tetrasubstituted Propargylamines via Hydroamination and Metalation of 1-Alkynes and Their Enantioselective Conversion to Trisubstituted Chiral Allenes.

Reaction of cyclic secondary amines with 1-alkynes and copper(I) chloride at 110-120 °C gives the corresponding alkynylcopper complex, which adds to the iminium ion intermediate formed in situ by hydroamination of 1-alkynes to give the corresponding propargylamine derivatives in up to 94% yield and 99% regioselectivity. The diastereomerically pure chiral propargylamines were obtained in 23-89% yield using optically active 2-benzyl morpholine and N-methyl camphanyl piperazine. These chiral propargylamines are readily converted to the corresponding trisubstitued chiral allenes in 71-89% yields with up to 99% ee upon reaction with ZnBr2 at 120 °C. The results are discussed considering mechanisms involving diastereoselective addition of alkynylcopper complex formed in situ to iminium ions formed in situ regioselectively to produce the corresponding propargylamines, which in turn give the chiral allenes with very high enantioselectivity via an intramolecular 1,5-hydrogen shift in the presence of zinc bromide.

Synthesis of chiral 2,3-disubstituted 1,4-diazabicyclo[2.2.2]octane derivatives.

Racemic 2,3-diaryl-1,4-diazabicyclo[2.2.2]octane (DABCO) derivatives are synthesized from the readily accessible piperazines in 50-64% yield by cyclization using ethylene bromide, triethylamine, and KI at 80 °C. The enantiomerically enriched 2,3-diphenylpiperazine and the 2,3-bis(1-naphthyl)piperazine derivatives are prepared by a resolution method using commercially available optically active acids, yielding the corresponding DABCO derivatives in 51-64% yield with up to 99% ee. This mild cyclization can also be applied to enantiopure camphanyldiamine derivatives, and the products are obtained in 72-86% yields.

Convenient methods for the synthesis of chiral amino alcohols and amines.

Simple, convenient methods have been developed using readily available, easy-to-handle reagents to access a variety of chiral amino alcohols and amines, which have considerable potential for applications in asymmetric organic transformations. Scholars from this laboratory in India have made significant contributions to this field, which is the subject of the current review.

Highly enantioselective synthesis of chiral allenes by sequential creation of stereogenic center and chirality transfer in a single pot operation.

Chiral allenes are readily accessed in a single pot operation in the reaction of terminal alkynes, aldehydes, chiral secondary amines, and zinc halides in good yields (up to 77% yield) and excellent enantioselectivities (up to 99% ee) in toluene at 120 °C. The reaction proceeds through initial formation of chiral propargylamine intermediates with creation of a new stereogenic center and subsequent chirality transfer via an intramolecular hydride shift to produce chiral allenes with high enantiomeric purities.