A fresh look at natural tropolonoids

Development and status of MINDO/3 and MNDO

Abstract1. Biology IN 1925 A.P. Dustin1 reported that certain chemical agents which he called “poisons caryoclasiques” were able to exert a toxic action on cell nuclei without apparently injuring the cytoplasm. It has since wide variety of compounds can act in this way(see, for example, reviews by Dustin2 and Astaldi et al.3), and, since they appear to be active only on dividing cells, they have sometimes been called mitotic poisons.

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New evidence on the mode of action of mitotic poisons.

Conjugated cyclic trienes without nonbenzenoid aromatic characteristic were successfully employed as fine-tunable dipolarophiles in the Cu(I)-catalyzed asymmetric azomethine ylide-involved 1,3-dipolar [3 + 6] cycloaddition for the first time, affording a variety of bridged heterocycles bearing piperidine moiety in good yield with exclusive regioselectivity and excellent stereoselectivity. 2-Acyl group is the key factor that determines the annulation preferentially through [3 + 6]-pathway, while 2-ester group modulates the annulation through [3 + 2]-pathway.

Catalytic Asymmetric 1,3-Dipolar [3 + 6] Cycloaddition of Azomethine Ylides with 2-Acyl Cycloheptatrienes: Efficient Construction of Bridged Heterocycles Bearing Piperidine Moiety

A novel protocol for the annulation of tropone to enals involving nucleophilic heterocyclic carbene (NHC) catalyzed homoenolate formation has been developed. Interestingly, the reaction led to bicyclic δ-lactones instead of the expected γ-spirolactones, presumably by the uncommon [8 + 3] annulation pathway. The strategy works well with a variety of enals.

An N-heterocyclic carbene-catalyzed [8 + 3] annulation of tropone and enals via homoenolate.

IN view of the remarkable physiological properties of colchicine its chemical nature is of some interest. Until recently, the structure (I) proposed by Windaus1 has been generally accepted, although the stability of colchicine did not suggest a 9-amino-9: 10-dihydrophenanthrene system, and although the salicylaldehyde enol structure of ring C appeared fantastic. Cohen, Cook and Roe2 have now provided evidence that ring B must be 7-membered, but the exact location of the acetamido group remains uncertain; the isolation by Windaus of 4-methoxyphthalimide from the oxidation product of acetylcolchinol methyl ether suggested that the group was adjacent to ring C, but Lettre and Fernholz3 have found that only β-anisylethylamine derivatives act as mitosis poisons.

M. J. S. Dewar

Papers

Structure of Colchicine