Lithiated allylic sulfoximines

In contrast to allylic phosphine oxides, phosphonates, sulfones and sulfoxides, the chemistry of lithiated allylic sulfoximines has been less extensively developed25 27. The reaction of lithiated racemic A-phenyl-A -(4-rnethylphenyl)-S -(2-propenyl)sulfoximine with either 2-cy-clopentenone or 2-cyclohexenone gave a complicated mixture with 1,4-oc-ad ducts being slightly favored over the 1,4-7-adducts. The yields of these adducts were poor25. In contrast, lithiated racemic Ar-tert-butyldiphenylsilyl-5-phenyl-5,-(2-propenyl)sulfoximine gives mainly 1,4-y-ad-ducts on reaction with the same enones26. 

The lithiation of the T-configured acyclic allyl sulfoximines T-13 with n-BuLi gave the corresponding lithiated allyl sulfoximines -15 [15] which upon treatment with 1.1 equiv ofClTi(OiPr)3 at-78 to 0 °C in THF furnished the bis (allyl) titanium complexes -16, admixed with equimolar amounts of Ti(OiPr)4, in practically quantitative yields (Scheme 1.3.5) [14, 16]. Surprisingly the bis (allyl) titanium complexes -16 together with Ti(OiPr)4 and not the corresponding mono (allyl) titanium complexes were formed. 

The treatment of the cyclic allyl sulfoximines 14 with n-BuLi gave the corresponding lithiated allyl sulfoximines 17, which upon reaction with ClTi(OiPr)3 afforded the cyclic bis (allyl) titanium complexes 18 and equimolar amounts of Ti(OiPr)4 in practically quantitative yields [14]. The hydroxyalkylation of the cyclic complexes 18 with saturated and unsaturated aldehydes also proceeded with >98% regioselectivity and >98% diastereoselectivity at the y-position and gave the corresponding Z-onti-configured homoallyl alcohols 5 in good yields [14]. 

The treatment of the lithiated allyl sulfoximines E-15 with 1.1-1.2 equiv of ClTi(NEt2)3 at -78 to 0°C in THF or ether afforded the corresponding mono (allyl) titanium complexes E-19 in practically quantitative yields (Scheme 1.3.7) [14, 16]. Similarly the Z-configured complexes Z-19 were obtained from the Z-configured allyl sulfoximines Z-15. Reaction of the titanium complexes E-19 with aldehydes at -78 °C took place at the a-position and gave the corresponding homoallyl alcohols 6 with >98% diastereoselectivity in medium to good yields (Scheme 1.3.8) [14, 16]. 

The crystal structures of three lithiated allylic sulfoximines have been reported.44,82 The X-ray crystal structure of lithiated 116/12-crown-4 complex showed solvent-separated contact ion-pairs of [Li(12-crown-4)2]+ and the allylic sulfonimidoyl anion.82 The anion adopts a conformation in which the p orbital at... 

The alkylation of the lithiated allylic sulfoximine 118 (R=Ph or CH2Ph) is completely regioselective and gives only a-alkylation products 119.75 The products were formed as mixtures of diastereoisomers, but the diastereomeric ratios were not reported. 

Lithiation and then methylation of the optically active allylic sulfoximine 120 gave the a-alkylation products 122 as a single diastereoisomer.79 The stereochemistry of this compound was deduced by its transformation to a compound of known stereochemistry. The stereochemical outcome of this reaction was rationalized as arising from methylation of the lithiated species 121 in which the p orbital at Ca is gauche to both the oxygen and nitrogen substituents of the sulfur atom. Methylation of 121 would be expected to occur syn to lithium and anti to the S-Ph group. 

The reaction of lithiated 123 with benzaldehyde gave a 5.3 1 mixture of the a-adduct 124 and the y-adduct 125, while a similar reaction with pivaldehyde produced only the a-adduct 124.75 These products were formed as mixtures of diastereoisomers, but the diastereomeric ratios were not reported. In related examples, a-adducts were exclusively obtained from the reaction of lithiated N-tert-butyldiphenylsilyl81 and N-methyl83 allylic sulfoximines with aldehydes. Again, these products were mixtures of diastereoisomers. 

Lithiation of racemic N-tosyl allylic sulfoximine 126 followed by quenching the reaction at -78 °C with benzaldehyde or isobutyraldehyde gave the a-adducts 130a and 130b, respectively, as mixtures of diastereoisomers.84 Interestingly, when these reactions were performed with an excess of the aldehyde (2 molar equiv) and... 

A combination of resolution and diastereofacial cyclopropanation has been used to prepare a variety of cyclopropyl ketones with high optical purity77. Optically active lithiated (S)-N,S-dimethyl-S-phenylsulfoximine (17) is added to prostereogenic enones such as 16, and the resulting diastereomeric allylic alcohols 18 are separated by column chromatography. Hydroxyl-directed Simmons-Smith cyclopropanation (see Section 1.6.1.5.1.2.) provides intermediates which are thermally decomposed to release the optically pure cyclopropyl ketones 20 and the sulfoximine 19. 

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