Asymmetric nucleophilic monofluorobenzylation of allyl and propargyl halides mediated by a remote sulfinyl group: synthesis of homoallylic and homopropargylic fluorides.

Fluorinated 2-(p-tolylsulfinyl)benzyl carbanions react with allyl and propargyl halides in a highly stereoselective way, providing homoallylic and homopropargylic fluorides, respectively, with high optical purity. Theoretical calculations found transition states for these transformations whose relative stabilities are consistent with the experimentally observed stereoselectivity.

Asymmetric nucleophilic monofluorobenzylation of carbonyl compounds: synthesis of enantiopure vic-fluorohydrins and α-fluorobenzylketones.

Asymmetric nucleophilic monofluoroalkylation of a broad range of aldehydes with an α-fluoro-γ-sulfinylbenzyl carbanion takes place with complete control of the facial selectivity at the carbanion and good to high anti-diastereoselectivity to give easily separable mixtures of two optically pure 1,2-fluorohydrin derivatives (up to 24:1 anti/syn). Separation and removal of the p-tolylsulfinyl group with tBuLi provides enantiomerically pure anti-1,2-disubstituted-1,2-fluorohydrins, whereas α-fluorobenzylketones can be obtained by desulfinylation of the mixture followed by pyridinium chlorochromate oxidation (one-pot process).

Synthesis of optically pure vic-sulfanyl amines mediated by a remote sulfinyl group.

Enantiomerically pure syn-1,2-diaryl-1,2-sulfanylamine derivatives can be obtained in a completely stereoselective manner by reaction of the benzylcarbanion Li-(S)-1 with N-phenyl (or PMP)-arylidene aldimines and further desulfinylation with t-BuLi. Theoretical studies at the DFT (mPW1PW91) level with the CPCM model, by using the Gaussian09 program, provide a good explanation for the stereochemical results.

2-(p-Tolylsulfinyl)benzyl halides as efficient precursors of optically pure trans-2,3-disubstituted aziridines.

Aziridination of (R)-N-sulfinylaldimines (aryl, heteroaryl and alkenyl derivatives) with 2-(p-tolyl sulfinyl)benzyl iodide in the presence of sodium hexamethyl disilazide takes place with almost complete control of the stereoselectivity (facial and anti/syn) and with very high yields affording optically pure N-sulfinyl trans-2,3-disubstituted aziridines 7. Simultaneous removal of both C- and N-p-tolylsulfinyl groups with tBuLi provides the corresponding trans-NH aziridines 8 without affecting their optical purity. Some experimental results suggest these processes evolve through benzyl halocarbenoids as intermediates, whereas theoretical calculations support the formation of benzyl carbanions.

Stereoselective control of planar alpha-dimethylsulfonium benzyl carbanions. Synthesis of optically pure trans-aziridines.

(R)-N-sulfinylimine and (S)-N-sulfinylimine react with the ylide derived from (S)-dimethyl-[2-(p-toluenesulfinyl)phenyl]sulfonium salt, affording trans-2,3-disubstituted aziridines. A complete trans selectivity in low facial diastereoselectivity is observed when the configuration at the sulfur atoms of the reagents is the same. Otherwise, when their configurations are different, the reaction evolved with total facial diastereoselectivity and the cis/trans ratio ranged between 1/4.