Total synthesis of sativene and copacamphene via a free radical cyclization

Abstract

ferent time intervals aliquots (4 ml) were withdrawn (under argon) and the resin separated immediately by suction filtration, washed thoroughly with DMF, CH2CI2, and MeOH, and then subjected to amino acid analysis. The rate of decrease in amino acid content was taken as the rate of photolysis of the -methylphenacyl ester anchoring bond. Exactly the same experiments were performed on tetrapeptide resins VII and VIII to determine the rate of photolytic cleavage of the o-nitrobenzyl and benzyl ester linkages. The results are summarized in Figure 1. For the studies of the rates of acidolysis or hydrazinolysis of the resins III, VII, and VIII, 0.5 g each of the samples were stirred individually in 20 volumes each of TFA-CH2CI2 (1:1) or 10% H2NNH2 (DMF) in six separate flasks. Aliquots (1 ml) from each reaction were taken at different times and treated as described above for the photolysis experiments. The results are also shown in Figure 1.

Free-Radical Rearrangements

“…The generation of 93 from 92 involves two successive 1,6 ring closures (257), and the formation of 95 by cyclization of 94 constitutes a key step in the synthesis of sativene and copacamphene (256). Thus, 89 generated by cyclization of 62 undergoes further 1,6 and 1,7 ring closure to afford 90 and 91 (795).…”

Organic Synthesis: New Vistas in the Brazilian Landscape

“…The gram-scale endpoint is a highly (Martins et al 1995). -1970- 's (Brocksom et al 1974 (Figure 49), and the pioneer total synthesis of sativene and copacamphene via a radical cyclization by Bakuzis (Bakuzis et al 1976) (Figure 50), the area of synthetic methodology in Brazil has grown steadly over the last five decades. Petragnani and Comasseto have enlarged the field of organoselenium and organotellurium chemistry and have trained generations of organic chemistry dedicated to this area, some of them already mentioned in previous sections (Comasseto et al 1997).…”

Química Orgânica no Brasil: sua contribuição na síntese total de produtos naturais desde a fundação da SBQ

“…A síntese total de moléculas no Brasil está intimamente ligada ao desenvolvimento do acordo CNPq/NAS e à fundação da SBQ e da revista Química Nova em 1978. Apesar de haver exemplos de sínteses anteriores, como a do sativeno e do copacanfeno via ciclizações radicalares 5 , já em 1978, no segundo número do periódico, há o primeiro relato de um trabalho de investigação sobre uma síntese total 6 . A síntese da β-metileno-χ-spirolactona foi fruto das investigações iniciais na área de química orgânica do acordo binacional, e permitiu posteriormente a síntese total da bakkenolida A 7 (Figura 1).…”