A new series of mono- and diphenylsubstituted silatranes and boratranes N(CH 2CH 2O) 2(CHR 3CR 1R 2O)MZ (M = Si, Z = CH 2Cl, C CPh, H, OMenth, R 1, R 2, R 3 = H, Ph; M = B, Z = nothing, R 1, R 2, R 3 = H, Ph) have been synthesized. Both transalkoxylation and stepwise modification of a preformed metallatrane skeleton were used. The chloromethyl derivatives N(CH 2CH 2O) 2(CHRCHRO)SiCH 2Cl (R = H, Ph) react with tert-BuOK under intramolecular cycle expansion to give 1- tert-butoxy-2-carba-3-oxahomosilatranes N(CH 2CH 2O)(CH 2CH 2OCH 2)(CHRCHRO)SiO t Bu (R = H, Ph). The treatment of boratranes N(CH 2CH 2O) 2(CH 2CR 1R 2O)B (R 1,R 2 = H, Ph) with triflic acid and trimethylsilyl triflate results in the products of electrophilic attack at the nitrogen atom. The molecular structures of four silatranes and one boratrane bearing phenyl groups in the atrane skeleton were determined by the X-ray structure analysis.