Complex glycans are directly involved in essential life processes, but it is challenging to precisely assemble them in sufficient quantities with high homogeneity. One major hurdle is that the stereoselectivity in glycosylation often varies with substrates, thus it is difficult to develop an exquisitely selective glycosylation method that is also broadly effective. In particular, searching for a general solution for stereoselective assembly of 1,2-cis-glycosidic bonds is an unsolved challenge.