title: Highly diastereoselective 1,3-dipolar cycloaddition reactions of trans-2-methylene-1,3-dithiolane 1,3-dioxide with 3-oxidopyridinium and 3-oxidopyrylium betaines: a route to the tropane skeleton.
abstract: The C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide, was found to react with a range of 3-oxidopyridinium betaines (bearing different substituents on nitrogen) in high yield and with total diastereoselectivity. A 2.3:1 mixture of regioisomers was formed with all of the 3-oxidopyridinium betaines but the ratio was found to change over prolonged periods of time due to reversibility of the minor regioisomer. 3-Oxidopyridinium betaines bearing methyl substituents at either the 2- or 6-position were also tested in the cycloaddition process. Improved regioselectivity (8:1) and again high diastereoselectivity were observed with the betaine having an additional substituent at the 2-position, but with betaines having a substituent in the 6-position although high regioselectivity was observed (9.9:1), the major isomer was formed with low diastereoselectivity (5.5:4.4). The origin of the regio- and diastereo-selectivity with all the betaines is discussed. Finally, the C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide was reacted with an oxidopyrylium betaine in moderate yield. Good regioselectivity and moderate diastereoselectivity were observed.
authors.affiliation: School of Chemistry, Bristol University, Cantock's Close, Bristol, UK BS8 1TS.
authors.forename: Varinder K
authors.initials: VK
authors.lastname: Aggarwal
authors.forename: Richard S
authors.initials: RS
authors.lastname: Grainger
authors.forename: Gary K
authors.initials: GK
authors.lastname: Newton
authors.forename: Peter L
authors.initials: PL
authors.lastname: Spargo
authors.forename: Adrian D
authors.initials: AD
authors.lastname: Hobson
authors.forename: Harry
authors.initials: H
authors.lastname: Adams
mesh_terms: D001622:Betaine / Q000737:chemistry*; D003500:Cyclization; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D011726:Pyridinium Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013454:Sulfoxides / Q000737:chemistry*; D014320:Triphenylmethyl Compounds / Q000737:chemistry; D014326:Tropanes / Q000138:chemical synthesis* / Q000737:chemistry; D014753:Vinyl Compounds / Q000737:chemistry
chemical_list: C410432:3-oxidopyridinium betaine; D011726:Pyridinium Compounds; D013454:Sulfoxides; D014320:Triphenylmethyl Compounds; D014326:Tropanes; D014753:Vinyl Compounds; D001622:Betaine