Michael addition desulfurative

The monographs (8,9) also present clear expositions of methods of synthesis. A recent communication addressing a short approach to both symmetrical and unsymmetrical tetrahydrofurofuran lignans is outlined in Scheme 32 (149). Michael addition of the sodium salt of the silyl monoprotected diol (155) to the a-sulfonylcinnamate (156) gave the ether (157) which on desulfurization and hydrolysis gave the hydroxy acid (158). Lactonization of (158) by the Mukaiyama method... 

A simple and straightforward application was outlined in the synthesis of hydrohydrastinine as depicted in Scheme 10. Michael addition of 3,4-methyle-nedioxyphenylmethyl amine to vinyl sulfoxide 36 took place smoothly in refluxing methanol. Pummerer rearrangement in acetic anhydride afforded acetoxysulfide 37 in 90% yield and this was then cyclized to 38 with BF3 etherate in 93 % yield. Sulfide 38, which was rather unstable, was desulfurized with Raney nickel in 80 % yield. Hydrolysis of the acetyl group followed by reductive methy-lation afforded hydrohydrastinine (39) in good yield [24]. 

Early in the 1990s, Kumar and co-workers described an asymmetric synthesis of (5)-naproxen by means of a thia-Michael addition of thiophenol to acrylate 115 (Scheme 31.39). Desulfurization followed by acid cleavage... 

A novel desulfurative Michael addition of ArSOH to enones, catalysed by bipyPd(OAc)2 (5mol%) in the presence of lequiv of 50% H2SO4, has been developed. The reaction proceeds at 90 °C in MeOH and affords the / -aryl ketones. ESI-MS/MS was used to identify the aryl Pd -sulfinic intermediate, aryl-Pd , and C=0-Pd complexes... 

Similarly, the magnesium enolate of t-butyl (/ )-(p-tolylsulfmyl)acetate adds to aldehydes and ketones. The subsequent reductive desulfurization yields the corresponding optically active -hydroxy esters (Scheme 27). This process can be utiliz for preparation of a synthetic intermediate (95) of maytan-sine with a selectivity of 93 7 (equation 23). Michael- q)e addition of r-butyl (/7)-(p-tolylsulfinyl)ace-tate to crotonic ester with NaH in DMF has also been reported, but the enantiomeric excess of the desulfurized product is very low (12%). ... 

The synthetic utility of this reaction was further demonstrated by a three-step asymmetric synthesis of (S)-naproxen 22 an anti-inflammatory agent [16]. The thiol addition/asymmetric protonation on acrylate 19c resulted in the Michael adduct (S)-21c in 46% ee followed by a Raney nickel mediated desulfurization and acid hydrolysis. (S)-Naproxen 22 was isolated in 85% ee after a single crystallization (Scheme 7.12). 

In a similar strategy, the organocatalyzed addition of p-keto BT-sulfones to JV-Boc-protected imines, followed by reduction or desulfurization of the resulting adducts, affords optically active trans-allylic amines 65 or p-aminoketones f Scheme 19.291. This reaction was extended to iV-aryl imines and BT-sulfones bearing an ester, an amide, or a ketone at the p-position to give the corresponding Michael acceptor 66 in good to excellent yields. 

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