Construction of azaspirocyclic skeletons mediated by the carbonyl of Weinreb amide: formal total synthesis of (±)-cephalotaxine

Facile stevens rearrangement of the Weinreb amide and the subsequent key steps mediated by the carbonyl of Weinreb amide led to the construction of azaspirocyclic skeletons of some typical alkaloids....

Racemic and Meso Crystal Structures of an Axial-Chiral Spirobi-(dinaphthoazepin)ium Salt: Emergence of an S4-Symmetric Molecule

To date, only a few instances of S4-symmetric organic molecules exist. In principle, spirobi-(dinaphthoazepin)ium cations can achieve this highly symmetric point group. Heating racemic 2,2′-bis(bromomethyl)-1,1′binaphthyl with aqueous ammonia afforded a mixture of rac- and meso-3,3′,5,5′-tetrahydro-4,4′-spirobi[dinaphtho[2,1-c:1′,2′-e]azepin]-4-ium bromide which was separated by fractional crystallisation. Both stereoisomers were characterised spectroscopically, and their crystal structures were determined and compared. The rac crystal structure differs significantly from the known enantiopure one. The meso molecules display a near-perfect S4 symmetry. Upon treatment with KOtBu, both isomers undergo Stevens rearrangement.

On the Mechanism of the Stevens Rearrangement

The reaction mechanism for the Stevens rearrangement is one of the most controversial reaction mechanisms in organic chemistry. This account will address that controversy reviewing the experimental as well as some computational results.1 Introduction2 Evolution of the Mechanistic Knowledge2.1 Stevens (1928)2.2 Stevens (1930)2.3 Stevens (1932)2.4 Campbell (1946)2.5 Hauser (1951)2.6 Kline (1952)2.7 Lepley (1969)2.8 Baldwin (1970)3 Computational Investigations4 [2,3]-Stevens Rearrangement?5 Conclusion