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 ).     

Dislocation theory as a 3‐dimensional translation gauge theory

We consider the static elastoplastic theory of dislocations in an elastoplastic material. We use a Yang‐Mills type Lagrangian (the teleparallel equivalent of Hilbert‐Einstein Lagrangian) and some Lagrangians with anisotropic constitutive laws. The translational part of the generalized affine connection is utilized to describe the theory of elastoplasticity in the framework of a translation gauge theory. We obtain a system of Yang‐Mills field equations which express the balance of force and moment.     

Die Aminopentadienal-Umlagerung

Contrary to the rearrangement of 3-amino-3-X-propenals, which easily gives 3-X-propenamides at low temperature, the postulated rearrangement (Scheme 1) of the vinylogous 5-amino-5-X-pentadienals 2 normally stops at the level of (2H-pyran-2-ylidene)ammonium salts 4 . The main reason is that salts of type 4 are highly delocalized low-energy, charged species which makes addition 4 → 5 of weak nucleophiles difficult. In this paper, the first examples of the so-called `aminopentadienal' rearrangement are reported. Ring-opening 4 → 6 is facilitated by nucleophilic counter ions like X=PhO (see Scheme 4) or by adding an excess of `nucleophilic auxiliaries' such as Et₃N or EtOH (see Scheme 2). In a quite interesting sequence of steps, 5-phenoxy-5-(pyrrol-1-yl)penta-2,4-dienal ( 2g ; X=PhO) is easily transformed into 5H-pyrrolo[1,2-a]azepin-5-one ( 9 ) (Scheme 5).