Synthesis Simpkins

PAULMIER Selenium Reagents Intermediates in Organic Synthesis PERLMUTTER Conjugate Addition Reactions in Organic Synthesis SIMPKINS Sulphones in Organic Synthesis WONG WHITESIDES Enzymes in Synthetic Organic Chemistry... 

N. S. Simpkins, Sulphones in Organic Synthesis [Tetrahedron Organic Chemistry], (J. E. Baldwin and R D. Magnus, eds.), Pergamon Press, Oxford, 1993. 

Giblin, G.M.P., Jones, C.D., Simpkins, N.S. (1997) A Concise Stereoselective Synthesis of Epi-batidine Employing Conjugate Addition to an Alkenyl Sulfone Intermediate as the Key Step. Syniett, 589-590. 

N. S. Simpkins, Sulphones in Organic Synthesis. Pergamon Press, Oxford, 1993. 

Simpkins et al. used an intramolecular variation of this allylsilane addition to oxonium cations for the synthesis of eight-membered rings [14]. Allylsilane 22, containing the oxonium ion precursor (acetal function) is transformed upon treatment with EtAlCl2 into the medium-sized ring 23 in moderate yield and stereoselectivity (Scheme 13.10). 

Synthetic interest in (—)-alloasamizoline has risen steadily ever since its structure was first announced in the mid-1980s. Trost and Van Vranken2 were the first to report a racemic synthesis, in 1990, and there later followed two enantiospecific syntheses by Kuzuhara et al and Simpkins and Stokes4 in 1991 and 1992, respectively. 

Mechanistic analysis of some key steps in the Simpkins (—)-allosamizoline synthesis... 

Sulphoxides, sulphates and sulphonyl compounds have also been used as substrates in stannane-mediated reductions. Gethin and Simpkins reported the Bu3SnH-mediated removal of the tosyl group in substrate (79) in their preparation of protected thymine polyoxin C (equation 53)293. Similarly, Xu and Lu described the removal of the tosyl group in 80 under similar conditions during their synthesis of pentabromopseudilin (equation 54)294. Padwa and his associates utilised B SnH to remove the sulphone moiety in cyclopentenone (81) (equation 55)295, while Wnuk and coworkers discuss... 

Simpkins, N. S. Sulphones in organic synthesis Oxford [England] New York Pergamon, 1993. 

The potassium enolate generated from 23 is regarded as an enantiomeric atropisomer. Recently non-biaryl atropisomers have been receiving more attention in asymmetric synthesis.19 Most of them employ atropisomers that are configurationally stable at room temperature, while attention in this chapter is focused on asymmetric reactions that proceed via chiral nonracemic enolate intermediates that can exist only in a limited time. An application of configurationally stable atropisomeric amide to a chiral auxiliary for stereoselective alkylation has been reported by Simpkins and co-workers (Scheme 3.10).20... 

Simpkins and co-workers were the first to use an asymmetric catalytic process in (-)-anatoxin-a synthesis (Newcombe and Simpkins, 1995) instead of resorting to the chiral pool strategy. Their total synthesis of (-)-anatoxin-a relied on an enantioselective enolisation reaction of a readily available ( )-3-tropinone (33), by a chiral lithium amide base (34) (Bunn et al. 1993a, 1993b) and subsequent cyclopropanation/ring expansion reaction giving the ketone 37 (Scheme 7.8). 

Newcombe, N.J., and Simpkins, N.S. 1995. A concise asymmetric synthesis of (—)-anatoxin-a using an enantioselective enolisation strategy. J Chem Soc Chem Commun 831-832. 

SCHEME 13.102 Simpkins s synthesis of methyl 3,6-anhydro-2-deoxy-L-a//o-heptonate. 

Cox, P J, Simpkins, N S, An enantioselective deprotonation route to a versatile intermediate for C-nucleoside synthesis, Synlett, 321-323, 1991. 

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