Pyridinesulfonyl Chloride

In the reaction of the tin(II) enolate derived from (1) with aldehydes, enantioselectivities are disappointingly low, while good diastereoselectivities are observed. Highly diastereo- and enan-tioselective aldol reactions of propionate derivatives with aldehydes have been achieved by using the ketene silyl thioacetal (7) instead of the tin(II) enolate. The complex (8) produced by mixing tin(n) triflate and the chiral diamine (6) works as an efficient chiral Lewis acid. The reaction of (7) with various aldehydes proceeds smoothly in the presence of (8) and dibutyltin diacetate in dichloromethane to afford the syn aldol adducts in high yields with almost perfect stereochemical control (eq 9).  

While stoichiometric amounts of tin(II) trifiate, (6), and the tin(rV) compound are necessary in the reaction shown in eq 9, the truly catalytic asymmetric aldol reaction of (7) with aldehydes is realized by using (8) as a Lewis acid catalyst (eq 10). The reaction is carried out in propionitrile hy slow addition of the substrates to the catalyst. 

Related Reagents. 3-(2-Benzyloxyacetyl)thiazolidine-2-thione 2,6-Dimethylphenyl Propionate 2-Methyl-2-(trimethyl-silyloxy)-3-pentanone l,3-Thiazolidine-2-thione Tin(II) Tri-fluoromethanesulfonate. 

Shu Kobayashi Science University of Tokyo, Tokyo, Japan 

A list of General Abbreviations appears on the front Endpapers 

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Isothiazolo[5,4-6]pyridine-l, 1-dioxides (513) have been prepared by a direct synthesis (Equation 46) (90M281). 3-Carboethoxy-4,6-diphenylpyridine-2-sulfonamide (512) cyclizes in butanol at reflux temperature to give 3-oxo-2,3-dihydro-4,6-diphenylisothiazolo[5,4-6]pyridine-l,1-dioxide (513) (50%). Similarly, the reaction of 3-cyano- and 3-acetyl-4,6-diphenyl-2-pyridinesulfonyl chlorides (514) with ammonia afforded the corresponding 3-amino- and 3-methylisothiazolo[5,4-6]pyridine-1,1-dioxides (515) (Equation 47). 

Target compound 238 is synthesized in 15 steps from readily available starting materials in 25% overall yield by utilizing Pd- and Mo-catalyzed asymmetric reactions to control the quaternary and tertiary stereogenic centers, respectively. The fluorine containing part is introduced at the final stage by the reaction of a ketone 239 with 5-(trifluoromethyl)-2-pyridinesulfonyl chloride 240" (Scheme 12.57). 

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