Sulfonimidoyl-Substituted Bis allyl titanium Complexes

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]. 

Reaction of the bis(allyl) titanium complexes 16 and 18 with aldehydes occurs in a step-wise fashion with intermediate formation of the corresponding mono (allyl) titanium complex containing the alcoholate derived from 4 and 5 as a ligand at the Ti atom. Then the mono(allyl)titanium complexes combine with a second molecule of the aldehyde. Both the bis (allyl) titanium complexes and the mixed mono(allyl)titanium complexes react with the aldehydes at low temperatures with high regio- and diastereoselectivities. Interestingly, control experiments revealed that for the reaction of the bis (allyl) titanium complexes with the aldehyde to occur the presence of Ti(OiPr)4 is required, and for that of the intermediate mono(allyl)titanium complexes the addition of ClTi(OiPr)3 is mandatory (vide infra). 

2 Sulfonimidoyl-Substituted Mono(allyl)tris(diethylamino)titanium Complexes 

However, a more detailed study of the reaction of the mono(allyl)titanium complexes -19 carrying different alkyl groups at the double bond with different aldehydes revealed in some cases the highly diastereoselective ( 98%) formation of significant amounts of the isomeric homoallyl alcohols 4 besides 6 (Table 1.3.1). 

The structure of the sulfonimidoyl-substituted homoallyl alcohols 4-7 in solution and in the crystal is characterized by an intramoleculare hydrogen bond between the OH group and the N atom of the sulfonimidoyl group. 

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Scheme 1.3.5 Synthesis of cyclic and acyclic chiral sulfonimidoyl-substituted bis(allyl)titanium complexes.

Fig. 1.3.4 Structure of the sulfonimidoyl-substituted bis(allyl)titanium complex 28 in the crystal. Selected bond lengths Ti—C 244 and 229 pm, Ti—N 209 and 221 pm.

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