Publication Date:
2011-05-11
Description:
The SnCl 4 -catalyzed reaction of (−)-thiofenchone (=1,3,3-trimethylbicyclo[2.2.1]heptane-2-thione; 10 ) with ( R )-2-phenyloxirane (( R )- 11 ) in anhydrous CH 2 Cl 2 at −60° led to two spirocyclic, stereoisomeric 4-phenyl-1,3-oxathiolanes 12 and 13 via a regioselective ring enlargement, in accordance with previously reported reactions of oxiranes with thioketones ( Scheme 3 ). The structure and configuration of the major isomer 12 were determined by X-ray crystallography. On the other hand, the reaction of 1-methylpyrrolidine-2-thione ( 14a ) with ( R )- 11 yielded stereoselectively ( S )-2-phenylthiirane (( S )- 15 ) in 56% yield and 87–93% ee, together with 1-methylpyrrolidin-2-one ( 14b ). This transformation occurs via an S N 2-type attack of the S-atom at C(2) of the aryl-substituted oxirane and, therefore, with inversion of the configuration ( Scheme 4 ). The analogous reaction of 14a with ( R )-2-{[(triphenylmethyl)oxy]methyl}oxirane (( R )- 16b ) led to the corresponding ( R )-configured thiirane ( R )- 17b ( Scheme 5 ); its structure and configuration were also determined by X-ray crystallography. A mechanism via initial ring opening by attack at C(3) of the alkyl-substituted oxirane, with retention of the configuration, and subsequent decomposition of the formed 1,3-oxathiolane with inversion of the configuration is proposed ( Scheme 5 ).
Print ISSN:
0018-019X
Electronic ISSN:
1522-2675
Topics:
Chemistry and Pharmacology
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