Syntheses of homochiral 1,2-ferrocene-functionalized Lewis acids and acid/base pairs

We report a facile approach for the synthesis of homochiral 1,2-disubstituted ferrocene-functionalized Lewis acids and acid/base pairs. The synthesis is based on chiral induction facilitated by the ortho sulfinyl subsitutent in S-Fc{S(O)p-tol}, S-1, to obtain the key intermediate S,Sp-1,2-fc{S(O)p-tol}(BMes2), S,Sp-2a (p-tol = C6H4Me-4, Mes = C6H2Me3-2,4,6). Subsequent substitution of the –S(O)p-tol substituent in S,Sp-2a gives access to a range of enantiomerically pure Sp-1,2-ferrocene-functionalized Lewis acids and acid/base pairs including the first homochiral 1-phosphino-2-borylferrocene. Enantiomeric excesses (e.e.s) of >95% have typically been achieved using this methodology.

A synthetically versatile method is presented to generate a class of homochiral bifunctional Lewis acids and acid/base pairs of the type Sp-1,2-fc(BMes2)(E) {E = PPh2, −P(O)Ph2, −B(OH)2, −B((+)-pinandiolate)} with enantiomeric excesses of >95%.Figure optionsDownload as PowerPoint slideHighlights
► Improved, atom-efficient synthesis of S,Sp-1,2-fc{S(O)p-tol}(BMes2).
► Substitution of the −S(O)p-tol group in S,Sp-1,2-fc{S(O)p-tol}(BMes2) offers access to a range of homochiral Lewis acids and acid/base pairs.
► Determination of the chirality of the resulting 1,2-difunctionalized ferrocenes reveals high enantiomeric excesses (>95%).