Intramolecular nitrone dipolar cycloadditions: control of regioselectivity and synthesis of naturally-occurring spirocyclic alkaloids.
The intramolecular nitrone dipolar cycloaddition of in situ-generated nitrones such as compound 26 has been used for the synthesis of cyclic isoxazolidines 27 and 29. The regioselectivity of the intramolecular cycloaddition depends on the nature of the terminal substituent on the dipolarophile. The influence of the substituent on the regioselectivity of the cycloaddition has been examined using several model systems and two methods of nitrone formation. These studies demonstrated that the cyano-substituent plays a special role in favouring the formation of the 6,6,5-ring fused adduct 27 under thermodynamically controlled conditions. The utility of the cyclo-adduct 57 (see Scheme 12) as a precursor for the naturally occurring histrionicotoxins is illustrated by the synthesis of three "unsymmetrical" (i.e. with each side chain bearing different functional groups) members of the histrionicotoxin family HTX-259A, HTX-285C and HTX-285E (2, 3 and 4 respectively).
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
Alastair J
AJ
Hodges
Joseph P
JP
Adams
Andrew D
AD
Bond
Andrew B
AB
Holmes
Neil J
NJ
Press
Stephen D
SD
Roughley
John H
JH
Ryan
Simon
S
Saubern
Catherine J
CJ
Smith
Michael D
MD
Turnbull
Annabella F
AF
Newton
D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry*; D000664:Amphibian Venoms / Q000138:chemical synthesis* / Q000737:chemistry*; D001688:Biological Products / Q000138:chemical synthesis* / Q000737:chemistry; D061565:Cycloaddition Reaction; D009589:Nitrogen Oxides / Q000737:chemistry*; D013141:Spiro Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013379:Substrate Specificity
D000470:Alkaloids; D000664:Amphibian Venoms; D001688:Biological Products; D009589:Nitrogen Oxides; D013141:Spiro Compounds; C015388:nitrones; C007948:histrionicotoxin