Further Synthetic Attempts towards Calicene

First synthetic attempts towards the so‐far‐unknown calicene (=5‐(cycloprop‐2‐en‐1‐ylidene)cyclopenta‐1,3‐diene) precursors 3‐(cyclopenta‐2,4‐dien‐1‐ylidene)tricyclo[3.2.2.2^2,4]nona‐6,8‐diene ( 4 ; Scheme 1), 1,4‐di(cyclopenta‐2,4‐dien‐1‐ylidene)cyclohexa‐2,5‐diene ( 5 ; Scheme 2), and (2‐bromocycloprop‐1‐en‐1‐yl)cyclopentadiene ( 6 ; X=Br; Scheme 5) are reported, which would represent very attractive compounds for gas‐phase pyrolysis ( 4 ), matrix photolysis ( 5 ), and low‐temperature HBr eliminations in solution ( 5 ).     

Synthesis of Aristotelia‐Type Alkaloids,Part XVI

Two independent total syntheses of the Aristotelia alkaloid (−)‐serratenone ((−)‐ 1 ) are disclosed, one starting with (−)‐α‐pinene, the other one with (S)‐α‐terpineol. These correlations led to a revision of the originally proposed absolute configuration of the natural product. In the course of systematic investigations of the behavior of the indole alkaloids (+)‐makomakine ((+)‐ 18 ) and (−)‐hobartine ((−)‐ 22 ) towards oxidizing reagents, it was found that treatment with I₂ leads to no less than five different products. Depending on the exact reaction conditions, each of them can be obtained as the major component in yields between 40 and 60%. One of these compounds was shown to be identical with the natural product (+)‐11,12‐didehydromakonin‐10‐one ((+)‐ 28 ).     

Film flow over strongly undulated bottom profiles at low Reynolds numbers – Experimental study

We study gravity driven films of a Newtonian fluid flowing down sinusoidal bottom profiles. We give experimental evidence of vortices in the film flow under creeping flow conditions down to Reynolds numbers of the order of 10^–5. The vortices are created in the valleys of the undulated bottom profile. They are visualized employing a particle image velocimeter with fluorescent tracers. It turns out that the vortices are generated beyond a critical film thickness.