Selective Methylation of the Ninhydrin-Phenol Adducts with I_2 in MeOH

摘要

The formation of ninhydrin-phenol adducts and chemical transformations of them have been studied by us and other groups.The adducts can be easily prepared from ninhydrin(1)and phenols 2 in acetic acid in good yields.The structure of the ninhydrin-phenol adduct 3 is benzo[b]-indeno[2,l-d]furanone skeleton in CDCl_3.However,the adduct 3 existed in equilibrium with its ring-opened form 3' in DMSO-d_6(Scheme 1).The structure can be easily confirmed from the ~1H NMR spectrum.For the cyclic form 3a,as an example,the protons at the ninhydrin moiety appeared as t,d,t,and d at around 7.49-8.02 ppm in CDCl_3(a in Figure 1).Whereas,3a and 3a' existed in a ratio of 65 :35 in the ~1H NMR spectrum in DMSO-d_6(b in Figure 1).The four protons of the ninhydrin moiety of 3a' appeared as a singlet apparently at 8.00 ppm due to the symmetric nature of the compound of 3a'(Figure 1).The characteristic peaks of 3a(t,d,t,d)remained in about 65% with slightly different chemical shifts.