2 -2-thio-4-oxazolidinones

Diels-Alder Cycloaddition Reactions. Catalysts 1 and 2 facilitate asymmetric Diels-Alder cycloaddition reactions between propenyl oxazolidinones (and thio-oxazolidinones) and dienes such as cyclopentadiene (eq 2). Both 1 and 2 display sim-... 

Scheme 6.130 Proposed mechanism of the 121-catalyzed enantioselective thio-Michael-aldol tandem reaction of 2-mercaptobenzaldehydes with a,P-unsaturated oxazolidinones bifunctional activation through thiourea 121.

Scheme 6.131 Typical thiochromanes obtained from the 121-catalyzed asymmetric thio-Michael-aldol tandem reaction between various 2-mercaptobenzaldehydes and a, 3-unsaturated oxazolidinones.

In search for control of absolute stereochemistry, the reaction of thio-chalcones was investigated with unsaturated amides bearing an Evans chiral oxazolidinone [223] and dimenthyl fumarate [224, 225]. For the first time with thiocarbonyl compounds, the efficiency of Lewis acid addition was demonstrated, and reactions could be conducted at room temperature. With EtAlCl2 (Table 4, entry 2) or A1C13 (entry 3), levels of induction up to 92% were attained for the endo isomer. Yb(OTf)3 in DMSO also caused the acceleration of the reaction with chiral acrylamides with p-facial selectivity [226]. This group has also reported [227] an intramolecular hetero Diels-Alder reaction with divinyl thioketones and the double bond of an allyloxy group (Table 4, entry 4). 

The use of hydroxy-ester 5.231 as a template required its conversion to phenyl-thio amino derivative 5.232. This carbamate was converted to oxazolidinone 5.233. and replacement of the phenylthio group with allyl (see 5.234) was followed by ring opening to give 5.235. As in the two previous examples, the alkenyl moiety was converted to the acid via oxidative cleavage, giving 4R-(N-Boc-N-methyl-amino)-5S-methyl-3R-methoxyheptanoic acid, 5.236. ... 

Fukuyama and coworkers have utilized Ir in the U-4CR to synthesize Af-acyl thio esters. The U-4CR product 146 can be converted to the corresponding Af-acyl oxazolidinone 147 by treating with BuOK in anhydrous THF in the presence of 4A molecular sieves. Unlike alkyl alkoxides (e.g., methoxide), phenoxide anion does not attack the Al-acyl oxazolidinone 147 because of weak nucleophilicity (pK = 10). Molecular sieves play a critical role in preventing hydrolysis of the starting... 

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