Oxazolidine-2-thione

Oxazolidine, cis-4-methyl-5-phenyl- C NMR, S, 20 (79MI40100) Oxazolidine-2-thione IR, S, 26 (63PMH(2)161)... 

These examples and those in Scheme 2.6 illustrate the key variables that determine the stereochemical outcome of aldol addition reactions using chiral auxiliaries. The first element that has to be taken into account is the configuration of the ring system that is used to establish steric differentiation. Then the nature of the TS, whether it is acyclic, cyclic, or chelated must be considered. Generally for boron enolates, reaction proceeds through a cyclic but nonchelated TS. With boron enolates, excess Lewis acid can favor an acyclic TS by coordination with the carbonyl electrophile. Titanium enolates appear to be somewhat variable but can be shifted to chelated TSs by use of excess reagent and by auxiliaries such as oxazolidine-2-thiones that enhance the tendency to chelation. Ultimately, all of the factors play a role in determining which TS is favored. 

Figure 13.1 Degradation of glucosinolates. Hydrolysis is catalyzed by myrosinases and gives rise to different degradation products dependent on the structure of the glucosinolate side chain and the hydrolysis conditions. (I) isothiocyanates, the major product at pH >7 (II) nitriles, the major product at pH <4 (ID) thiocyanates, produced from 2-propenyl-, benzyl-, and 4-methylthiobutylglucosinolates (IV) oxazolidine-2-thiones, produced from glucosinolates with P-hydroxylated side chains, (V) epithionitriles, produced in the presence of epithiospecifier proteins.

From a structural point view, the most explored thionocarbamates in carbohydrate chemistry are five-membered l,3-oxazolidine-2-thiones.27 29 With respect to the synthesis of aromatic analogues of OZTs-1,3 oxazoline-2-thiones (OXTs), only two acyclic D-fructose-derived OXTs were recently reported by Rollin and co-workers.30... 

The differences in reactivity between the nitrogen and the sulfur atom in OZTs reveal that most reactions can be interpreted with reference to Pearson s HSAB theory.56 In the case of l,3-oxazolidine-2-thiones, one may consider the nitrogen atom as a harder basic center than the softer sulfur atom. 

Among chiral auxiliaries, l,3-oxazolidine-2-thiones (OZTs) have attracted much interest for their various applications in different synthetic transformations.2 Such simple structures, directly related to far better known chiral oxazolidinones,11,12,57 have been explored in asymmetric Diels-Alder reactions and asymmetric alkylations, but mainly in condensation of their /V-acyl derivatives with aldehydes. Chiral OZTs have shown interesting characteristics in anti-selective aldol reactions58 or combined asymmetric addition. 

To increase the yields of the ring closure reactions, a new method was developed that was successfully applied for the synthesis of alicyclic fused systems of both the parent oxazolidine-2-thione and tetrahydro-1,3-oxazine-2-thione (85S1149). As an example, the synthesis of 2-thioxoperhydro-l,3-benzoxazine 103 is described. The dithiocarbamate 101, prepared from the amino alcohol 100, carbon disulfide and triethylamine, was treated with ethyl chloroformate in the presence of triethylamine, to give the thioxo derivative 103 via the transition state 102 (85S1149). In this way, the fused-skeleton thioxooxazines (91, X = S, 92) can be prepared with considerably higher yields (50-70%) than by the earlier methods (85S1149). 

Acyl-l,3-oxazolidine-2-thiones, chiral (1). Nagao and co-workers1 have prepared the chiral 3-acetyl-l,3-oxazolidine-2-thiones (la and lb) and used them to effect diastereoselective aldol reactions. The two chiral auxiliaries show, as expected, opposite diastereoselectivities, but contrast with the diastereoselectivities observed with chiral 4-alkyl-2-oxazolidones (11, 379-381). This aldol reaction has been used to prepare the chiral azetidinone 4 (equation I) and (-I- )-Prelog-Djerassi lactone. 

Chiral thiazolidine-2-thiones and oxazolidine-2-thiones. E. Fujita and Y. Nagao, Adv. Heterocycl. Chem., 45, 1 (1989). 

Reaction of the carbohydrate-based cyclic sulfites with NaSCN was used for the synthesis of f -l, 2-liised oxazolidine-2-thiones (Table 4) <1995TL5347>. Seleno and oxo derivatives were obtained with KSeCN or NaOCN, respectively <2000MI397>. The stereochemistry of products can be explained by the intermediate isomerization of /3-thiocyanates into cr-isothiocyanates (Scheme 10) <1995TL5347, 2000MI397>. 

Few studies have directly compared the effects of different hydrolysis products derived from the same glucosinolate. Such comparative studies with insects are listed in Tables 5.1-3, and comparative studies with other organisms in Table 5.4. In many cases, isothiocyanates seem to have greater biological activity than nitriles, thiocyanates, and oxazolidine-2-thiones. However, comparisons are complicated by differences among the hydrolysis products in physico-chemical properties, such as volatility. If two hydrolysis products differ significantly in volatility, for example,... 

Vinyl oxazolidine-2-thione Brassica okracea (Brussels sprouts), anti-insect, insect repellent] Bitter [affects insect... 

Silva S, Tardy S, Routier S et al (2008) 1, 3-Oxazoline- and 1, 3-oxazolidine-2-thiones as substrates in direct modified Stille and Suzuki cross-coupling. Tetrahedron Lett 49 5583-5586... 

The 2-aryloxazolines (v) have been synthesized under microwave activation by the direct Stille and Suzuki cross coupling reactions of l,3-oxazolidine-2-thiones (OZT) (iv) using (vi) as the coupling agent [14]. 

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