1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.7 Approaching Polyexocyclic Cycloketo-Porphyrin Systems
By considering the formation of poly-annulated systems, one has to keep in mind that the
formation of a ketone exocycle, like it is present in 53, causes dissymmetry within the
system as the closure process might occur from above or below the porphyrin plane. This is
of less relevance for mono-functional precursors as then enantiomers are formed (e.g.
simplified representable by � and �) having the same chemical and physical properties. By
switching to bis-functional precursors, this fact becomes of vital importance as different
kinds of ring closure can provide compounds of diastereomeric relation with different
chemical and physical characteristics. Additionally, one second aspect concerning
regiochemistry has to be included into considerations, as in mono-functionalized precursors
both pyrrolic units, the ring closure can occur to, are equivalent. If one annulation has taken
place, these units become differentiable providing additional possible products. Thus, from
one bis-functional starting compound, in principle four products can be obtained in one
reaction; pictorially represented by ��, ��, �� and ��, (see Scheme 46) plus
corresponding enantiomers.
Evidently, some control in terms of pre-organization has to be exerted to prevent ending up
in inseparable mixtures. Fortunately, the already introduced building-blocks (Scheme 17)
provide the capability to control at least some regiochemistry since they are accessible as
compounds with defined and stable αα- (48) and αβ-conformation (47). 69 Starting from a
precursor like 46 represents an even simpler alternative as there both functional groups are
situated on the same phenyl ring allowing only one possible ring closure scenario to give
enantiomeric structures.
The following paragraphs will hence concentrate on bis-functional compounds derived from
the abovementioned possible starting materials 46, 47 and 48 whose syntheses have already
been presented in paragraph 3.2.1. A pictorial outline showing the relations between them
and the corresponding bis-cycloketo-porphyrins is included in Scheme 46.
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