Activation of aryl ethers and aryl sulfides by the Fe(eta(5)-C5H5)(+) group for the synthesis of phenol dendrons and arene-centered poly-olefin dendrimers

Organo-iron mediated syntheses of dendrons and dendrimers are described. Th e reaction of [FeCp(eta(6)-p-EtOC6H4Me)][PF6], 1, with (BuOK)-O-t or KOH an d allyl bromide in THF gives both the triallylation of the acidic Me substi tuent and the heterolytic cleavage of the O-Me bond, which leads to the tri allyl oxocyclohexadienyl complex FeCp[eta(5)-p-(allyl)(3)CC6H4=O]. 2. If ex cess (BuOK)-O-t is added, the major compound obtained in this one-pot, eigh t-step reaction is the iron-free phenol derivative p-(allyl)(3)CC6H4OH, 3, in 50% yield. Surprisingly, the analogous aryl sulfide complexes [FeCp(eta( 6)-p-RSC6H4Me)][PF6], 4a (R = Me) and 4b (R = Et), also give 3 [together wi th (allyl)(3)CC6H4SR, 5] by reaction with (BuOK)-O-t and allyl bromide. The dendron 3 reacts with 1,3,5-C6H3[C(CH2CH2CH2X)(3)](3), 6, giving the 27-al lyl dendrimer 7 (first generation) whose purity, monitored by MALDI-TOF mas s spectroscopy, is not as good when the reaction is performed with X = I (6 a) as with X = mesylate (6b). Iteration of this divergent synthesis gives t he 81-allyl dendrimer 10 (second generation) and ultimately the dendrimer 1 3 (third generation) with a theoretical number of 243 allyl groups. Protect ion and functionalization of 3 also allows to carry out convergent dendriti c syntheses: reaction of 3 with the protected functional dendron C2H5C(O)OC 6H4C(CH2CH2CH2I)(3), 17, followed by deprotection gives the phenol nona-all yl dendron OHC6H4C[CH2CH2CH2O-p-C6H4C(CH2CH=CH2)(3)](3), 18. Compound 18 re acts with the 1,3,5-C6Me3(CH2Br)(3) and C-6(CH2Br)(6) cores to cleanly give the corresponding arene-centered 27-allyl and 54-allyl dendrimers 20 and 2 1, as shown by the dominant molecular peaks in the MALDI-TOF mass spectra. Reaction of 17 with 18 followed by deprotection does not give the expected 27-allyl dendron, but (very selectively) a 19-allyl dendron 19 resulting fr om selective double branching and single dehydroiodation, which shows the l imits of the convergent strategy.