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.
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.
Aggarwal
Varinder K
VK
School of Chemistry, Bristol University, Cantock's Close, Bristol, UK BS8 1TS.
Grainger
Richard S
RS
Newton
Gary K
GK
Spargo
Peter L
PL
Hobson
Adrian D
AD
Adams
Harry
H
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
C410432:3-oxidopyridinium betaine; D011726:Pyridinium Compounds; D013454:Sulfoxides; D014320:Triphenylmethyl Compounds; D014326:Tropanes; D014753:Vinyl Compounds; D001622:Betaine