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Life existed on Earth under anaerobic conditions long before the blue-green algae started to make oxygen.

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Nitroalkenes, or their fi-acetoxynitro precursors, react with a-isocyanoacetate esters in the presence of base to give high yields of 5-unsubstituted pyrroles; some important pyrroles are easily synthesised by this method.We have recently reported1 a convenient method for the synthesis of pyrroles from nitroketones using diphenyl disulphide-tributylphosphine as reductant. We now report another new route to pyrroles unsubstituted in position 5 and, therefore, particularly relevant to the porphyrin field. Central to this method is the ability of the nitro group to depart as nitrite under certain conditions.2 Thus base-catalysed Michael addition of an a-isocyanoacetate (1) to a nitroalkene (2) followed by cyclisation of the nitronate anion (4) onto the isocyano group would lead to the pyrroline ( 5 ) (Scheme 1). Similar isonitrile cyclisations have been used extensively by Schollkopf, Van Leusen, and others for the preparation of various heterocycles.3 Base-catalysed expulsion of nitrite from the pyrroline and double bond rearrangement would finally give the pyrrole (6) (Scheme 1).This conception was easily reduced to practice. Thus, addition of the P-nitrostyrene derivative (2a) to a mixture of t-butyl a-isocyanoacetate (la) and the guanidine base (7)4 in tetrahydrofuran-propan-2-01 at room temperature resulted in a smooth reaction to give the expected pyrrole (6a) in 90%

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