The oxazaborolidine (g)-catalyzed reduction of acetylporphyrins (4) led to enantiomerically pure hydroxyethylporphyrins (5), which were transformed into optically active chlorin derivatives (7 and 8 ) upon reaction by N,N-dimethylacetamide dimethyl acetal followed by hydrogenation. The absolute configuration of the synthesized chlorins was elucidated by means of their CD spectra.
Factor I (2)[2,3] and sirohydrochlorin 3a are porphinoid One of the main difficulties in model and total synthepigments with a chlorin and an isobacteriochlorin structure, ses"] of these structure types is the construction of the respectively. Their reduced derivatives occur as key inter-geminally dialkylated moiety in the pyrrole rings A or A mediates in the biosynthesis of vitamin B$]. Iron-contain-and B. In a former investigation we showed that this moiety ing sirohydrochlorin 3b, moreover, functions as the pros-can be easily constructed by starting from readily accessible thetic group of sulfite and nitrite reductases of bacteria hydroxyalkylporphyrins by Claisen rearrangement with and p l a n t ~[ ~, ~] .
N,N-dimethylacetamide dimethyl acetal['~sal. Apart from