N-methylsulfonimidoyl-substituted (2-alkenyl)titanium complexes: Application to the synthesis of beta- and delta-sulfonimidoyl-substituted chiral homoallylic alcohols, X-ray crystal structure analysis, and fluxional behavior

Enantiopure acyclic (E)- and (Z)-configured allylic sulfoximines have been synthesized from N,S- dimethyl-S-phenylsulfoximine and aldehydes by the add ition-elimination-isomerization route through the intermediate generation o f the corresponding (E)-configured vinylic sulfoximines. Isomerization of t he vinylic sulfoximines with DBU preferentially afforded the corresponding (Z)-configured allylic sulfeximines, which were subsequently isomerized by DBU to preferentially yield the (E)-isomers. Titanation of lithiated (E)-co nfigured allylic sulfoximines with ClTi(OiPr)(3) furnished the correspondin g bis(2-alkenyl)diisopropyloxytitanium(IV) complexes, which reacted with al dehydes in the presence of ClTi(OiPr)(3) with high regio- and diastereosele ctivities at the gamma -position to give the corresponding (Z)-anticonfigur ed delta -N-methylsulfonimidoyl-substituted homoallylic alcohols in good yi elds. In the absence of ClTi(OiPr)(3) at low temperatures, only one allylic moiety of the bis(alkenyl)diisopropyloxytitanium complex is transferred to the aldehyde. In this way, a cyclic lithiated allylic sulfoximine has been converted with high regio- and diastereoselectivity to the corresponding h omoallylic alcohols bearing a vinylic sulfonimidoyl group. Titanation of li thiated (E)- and (Z)-configured allylic sulfoximines with ClTi(NEt2)(3) aff orded the corresponding mono(2-alkenyl)tris (diethylamino)titanium(IV) comp lexes, which reacted with aldehydes with moderate to high regioselectivitie s and high diastereoselectivities preferentially at the alpha -position to give the corresponding syn-configured beta -N-melhylsulfonimidoyl-substitut ed homoallylic alcohols along with the (Z)-anti-configured delta -N-methyls ulfonimidoyl-substituted homoallylic alcohols in good yields. In this way, the cyclic lithiated allylic sulfoximine was converted with high regio- and diastereoselectivity to the corresponding isomeric homoallylic alcohols be aring an allylic sulfonimidoyl group. In the case of mono(alkenyl)tris(diet hylamino)titanium( complexes, the regioselectivity of their reactions with aldehydes has been found to depend on the size of the substituent at the CC double bond and the aldehyde, as well as on the configuration of the doubl e bond, Reaction of racemic Lithiated N-methyl-S-(3,3-diphenyl-2-propenyl)- S-phenylsulfoximine with ClTi(OiPr)(3) afforded the corresponding bis(alken yljdiisopropyloxytitanium(IV) complex. X-ray structure analysis revealed a distorted octahedral cis,cis,cis-configured bis(2-alkenyl) diisopropyloxyti tanium(IV) complex, in which the allylic moieties are coordinated in a bide ntate fashion through C-alpha and the N atom to the Ti atom, both having th e relative configuration RSSC. In solution, the titanium complex shows fIux ional behavior. which is characterized by topomerization of the isopropylox y groups and allylic moieties. The exchange of the latter occurs with reten tion of the configuration at C-alpha.