NONIONIC SUPERBASE-PROMOTED SYNTHESIS OF OXAZOLES AND PYRROLES - FACILE SYNTHESIS OF PORPHYRINS AND ALPHA-C-ACYL AMINO-ACID ESTERS

The reaction of acyl chlorides or acid anhydrides with isocyanoacetates in the presence of the superior strong nonionic base P(MeNCH(2)CH(2))(3)N (1) gave oxazoles in 98-99% yield. Treatment of the oxazoles with HCl-MeOH gave alpha-C-acyl amino acid esters in 81-82% yield. The reaction of beta-acetoxy-alpha-nitroalkanes or nitroalkenes with isocyanoacetates in the presence of 1 gave pyrroles in 100% yield. The conjugate acid of 1 can be treated with KO-t-Bu to regenerate 1. Treatment of the pyrroles with LiAlH4, followed by PTSA-CH2(OMe)(2) and oxidation gave porphyrins in 65-69% yield. LiCl, which functions both as a strong nucleophile in the S(N)2 demethylation of the 5,5'-bis(methoxycarbonyl)-3,3',4,4'-tetramethyldipyrromethane 22a and as a Lewis acid in the electrophilic substitution cyclization of paraformaldehyde at dipyrromethane, facilitates the combination of four reactions into a one-pot synthesis of octaethylporphyrin in 67% yield from 22a.