Dipyrromethenes chlorids

With the catalysis of strong Lewis acids, such as tin(IV) chloride, dipyrromethenes may aiso be alkylated. A very successful porphyrin synthesis involves 5-bromo-S -bromomethyl and 5 -unsubstituted 5-methyl-dipyrromethenes. In the first alkylation step a tetrapyrrolic intermediate is formed which cyclizes to produce the porphyrin in DMSO in the presence of pyridine. This reaction sequence is useful for the synthesis of completely unsymmetrical porphyrins (K.M. Smith, 1975). 

Figure 10 Time-dependent efflux of chloride ions from 200 nm vesicles loaded with a solution of NaCl (500 mM) and suspended in a solution of NaNOs (500 mM) and triethylsilane (5mM), adjusted to pH 7.4. Prodigiosins are indicated by filled markers (16 , 19 I, 20 ) dipyrromethenes are indicated by open markers (17 , 18 0).

A highly eleetrophilic carboxylie aeid derivative (aeid anhydride, acyl chloride or aldehyde) is usually used to generate the dipyrromethene precursor with two pyrrole units (Scheme 7.1). The synthetie proeedure introduces the... 

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