A phosphine-catalyzed tandem cyclization reaction has been developed to provide a series of chromeno [4,3-b]pyrrole derivatives, which contain three consecutive asymmetric centers. The reaction has a good yield, excellent stereoselectivity, and Z/E selectivity. The new method is simple, requires only mild conditions, and shows tolerance for various functional groups. Similarly, this reaction can be catalyzed by a chiral phosphine catalyst to achieve asymmetric synthesis. cascade cycloaddition strategy for facily synthesizing chromenopyrrole derivatives from aldimine esters and δ-acetoxy allenoates. In particular, a wide range of products have been afforded in generally good yields with excellent diastereoselectivities. In addition, by using a chiral phosphine catalyst, the cycloaddition reaction can also initially realize the asymmetric synthesis of chromeno [4,3-b]pyrrole. This protocol can be expected to find wide synthetic application because of its simple operation, mild reaction conditions, high efficiency, and high chemo-and enantioselectivity.

Comprehensive Summary Group B Streptococcus (GBS) is the major pathogen that causes invasive infectious diseases in neonates and infants. The development of preventive and therapeutic strategies against GBS infection has been becoming the most pressing subject worldwide. Group B carbohydrate (GBC), the group B‐specific polysaccharide that distinguishes GBS with other streptococci species, has been identified as an attractive antigen for diagnosis and vaccine development because of its highly conservative tetra‐antennary structure. In this paper, a highly convergent [3 + 5] glycosylation strategy for efficient synthesis of an octasaccharide derivative related to GBC oligosaccharide unit II has been developed. In this synthesis, each glycosylation reaction was efficiently constructed with glycosyl imidates, especially trifluoroacetimidate, as donors, and each glycosidic bond was stereoselectively controlled via the neighboring group participation effect of acyl group on the 2‐O‐position of imidate donors or the solvent effect of Et2O. Furthermore, the aminoethylphosphate group was smoothly installed on the 6‐O‐position of d‐glucitol residue using the phosphoramidite method. After global deprotection, the target octasaccharide was successfully obtained from d‐glucitol in 29 steps with an overall yield of 1.37%. The free amino group installed on the aminoethylphosphate spacer of the target molecule enables its modification with functionalized biomolecules for further biological studies.

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