The synthesis of the porphyrins (2c-j) has been achieved by the oxidative cyclization of appropriately substituted biladienes-ac. The availability of authentic material has allowed the finalization of the structure of a series of aetiotype fossil porphyrins which vary in substitution pattern at positions 3 and 13. All
combinations of H, Me and Et at these positions have now been isolated from natural sources. This points to a common precursor, possibly a divinylporphyrin, and strengthens the belief that the chlorophylls are the prime source of the petroporphyrins. A vinyl group, or a close derivative, is found at position 3 of all chlorophylls while fragmentation of the ubiquitous isocyclic ring of the chlorophylls could yield the vinyl group at position 13.
The intramolecular cyclization of porphyrins substituted with an acetic acid side chain has been studied under a range of conditions but the yield of product bearing a fused five- membered ketonic ring system was disappointingly low. Deoxophylloerythroaetioporphyrin (DPEP) derivatives with hydroxy groups at either C 13′ or C 15′ have been prepared by reduction of the corresponding ketones. 1H n.m.r . data for the latter alcohol matches well that reported for a porphyrin obtained from Marl Slate and which is probably derived from DPEP, by oxidation, during the extraction process.
The preparation of a series of porphyrins substituted with butyric acid side chains is described and efforts to achieve the intramolecular cyclization of this substituent are discussed. Attempts to prepare a stable spiro ketone by cyclization onto a β- pyrrolic carbon have not met with success but the synthesis of a seven- membered ring ketone by cyclization onto a meso -carbon has been completed. Reduction of this ketone has led to the synthesis of the petroporphyrin (1d). Some comments are offered concerning the origin of the isomeric petroporphyrin (19a) which bears a methylated six- membered ring sytem fused to the porphyrin macrocycle.
The synthesis of the petroporphyrins (3e) and (4e) has been completed, and their presence as the nickel complexes (3a) and (4a) in the Julia Creek shale oil deposits has been confirmed. While the derivation of (4e) from a chlorophyll c is generally accepted, it is proposed that (3e) may also originate from this group of pigments, thus highlighting the importance of these photosynthetic pigments as a source for fossil porphyrins.
Several approaches to the synthesis of porphyrins bearing fused six- membered ring systems were explored with the aim of obtaining the petroporphyrin (4a). This was ultimately achieved by an intramolecular cyclization of a porphyrin with a propanoyl chloride side chain in the presence of stannic chloride. Methylation of the intermediate ketone with CH3Li and reduction of the resultant alcohol with NaBH3CN/Znl2 furnished (4a).
A new demethyl analogue of DPEP, present as a nickel(II) complex in the Julia Creek oil shale deposit of North Queensland, has been shown by ring synthesis to lack a methyl group in ring A. This is now the third demethyl analogue of DPEP to be identified.
ChemInform Abstract The title compound (V) is synthesized by a strategy involving formation of the porphyrin macrocycle (III), followed by cyclization of a propanoyl chloride side chain in the presence of SnCl4. The macrocycles fused with a six-membered ring system are of interest in connection with the question, if petroporphyrins found in petroleum and similar deposits in general have their origin in chlorophylls which were part of living systems of past geological ages (yields in g).
A new synthesis of the 13′-methyl (1a) analogue of dpep is described commencing with the methylation of phylloerythroetioporphyrin (1d) with subsequent reduction of the derived tertiary alcohol. The availability of this synthetic material has allowed the presence of this petroporphyrin as its nickel complex to be confirmed in the Julia Creek oil shales. The presence of an isomer of this petroporphyrin has been noted in the same deposit, and the structure of this novel fossil porphyrin has been confirmed as the 15′-methyl analogue (1b) of dpep by a synthesis commencing from the 15′-oxoporphyrin (1e). In addition, the 15′- and 13′-methyl analogues of dpep have been synthesized by cylization of appropriately substituted propenyl- and isopropenyl-porphyrins respectively. The origin of these two petroporphyrins is discussed.
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