Asymmetric synthesis of [3](1,1′)- and [3](1,1′)[3](3,3′)-ferrocenophanes

(R)alpha-Ferrocenyl alcohols underwent conversion to their corresponding methyl ethers on treatment with MeOH/AcOH, which were in turn converted to ethyl 3-ferrocenylpropanoates when combined with 1-ethoxy-1-(trimethylsilyloxy)ethene and BF3.OEt2. After ester hydrolysis, the resulting acids (92-96% ee) underwent heteroannular Friedel-Crafts cyclization to give singly bridged ferrocenophanes of high enantiomeric purity. The methanolysis and silyl ketene acetal addition sequence was also applied to (R,R)-1,1'-bis(phenylhydroxymethyl)-ferrocene, and to (R,R-)-1,1'-bis((4-bromophenyl)hydroxymethyl)ferrocene, to give the corresponding diacids (94% ee) after ester hydrolysis. On Friedel-Crafts cyclization, the first of these diacids gave a 7:37:56 ratio of singly bridged ferrocenophanes after conversion of the remaining acid functionalities to methyl esters. The least abundant product was identified as (R-p)-1,1'-(R)-(1-oxo-3-phenyl-1,3 -propanediyl)-2-(R)-(3-methoxy-3-oxo-1-phenylpropyl)ferrocene by an X-ray crystal structure analysis. After separation, the most abundant isomer was converted in four steps to the novel doubly bridged C-2-symmetric ferrocenophane (R,R,S-p,S-p)-1,1'-(1-phenyl-1,3-propaned characterized by an X-ray crystal structure analysis. The remaining isomer was converted to the corresponding 1,1',3,3'-(R,R,R-p,R-p)-ferrocenophane. Also synthesized by this method was (R,R,S-p,S-p)-1,1'-(1-(4-bromophenyl)-1,3-propanediyl)-3,3'-(3-(4-bromophenyl)-1,3-propanediyl)ferrocene, which after bromine-lithium exchange was converted to the corresponding dicarboxylic acid. (R,R,S-p,S-p)-1,1'-(1-Phenyl-1,3-propanediyl)-3,3'-(3-phenyl-1,3-propanediyl)- ferrocenium tetrafluoroborate catalyzed the reaction between methacrolein and cyclopentadiene, although no enantioselectivity was observed in the resulting Diels-Alder adducts.