Aldehydes 1.3- dithiane dioxide reactions

Aggarwal has discovered that the anion derived from 1,3-dithiane dioxide undergoes rapid reaction with a range of aldehydes leading to the formation of diastereoisomeric mixtures in good yield (Scheme 20).76b... 

Halo-1,3-dithiane trans-l,3-dioxides (80 X = Cl, Br) act as diastereoselective carbonyl anion equivalents in reactions with aldehydes.117 The scope of the reaction has been explored by varying the temperature, the aldehyde, and the metal used as counterion. Similarly, metal 1,3-dithianides (81 M = Li, Cu1) can be added diastereoselec-tively to chiral aldehydes subsequent hydrolysis yields an a-hydroxyaldehydc.118... 

The scope and limitations of the metal anions of 2-halo-l,3-dithiane trans-1,3-dioxide as diastereoselective carbonyl anion equivalents has been explored with regard to reaction with aldehydes.79 Reactions of metallated trans-, 3-dithiolanc 1,3-dioxide (five-membered ring) with aldehydes under kinetic and thermodynamic control have also been studied and contrasted with those of the metallated monooxide, parent sulfide, and 1,3-dithiane 1,3-dioxide (six-membered ring).80... 

Lithiated 2-chloro- 1,3-dithiane- 1,3-dioxide undergoes an analogous addition reaction with aldehydes to give product mixtures displaying high diastereoselec-tivities (Scheme 21)77... 

Enantioselective synthesis ofa-hydroxy acid derivatives. Recently, Aggarwal has reported an enantioselective approach to the synthesis of a-hydroxy acid derivatives using trans- 1,3-dithiane- 1,3-dioxide. For example, reaction of trans-1,3-dithiane-1,3-dioxide with an aromatic aldehyde liberates the alcohol which is protected as the tetrahydropyranyl (THP) ether the resulting product may then be subjected to a Pummerer reaction, using trifluoroacetic anhydride, to give a thiolester. Transthiolesterification of this product using LiSEt gives the... 

Dropwise addition of butyllithium to a solution of ( )-l,3-dithiane 5,5 -dioxide (110) in pyridine-THF (1.5 1) generates an anion (111), which reacts with an aldehyde to give an adduct (112) as a 1 1 diastereomeric mixture. The reaction is extremely rapid at -78 °C, but the kinetic selectivity is moderate. In the reaction with benzaldehyde or pivalaldehyde, equilibration is attained at 0 C to give predominantly a single diastereomer in good yield (Scheme 31). ... 

Although chlorohydrins are obtained in good yield and with high diastereoselectivity by the reaction of the anion derived from 2-chloro-1,3-dithiane 1,3-dioxide with aromatic aldehydes, subsequent ring closure to the epoxide is prevented by a competing retro-aldol reaction <97JCS(P1)11>. 

Anionic Additions to Aldehydes. The /dCa of trans-, >-dithiolane 1,3-dioxide has been determined by Bordwell and disclosed by Aggarwal to be 19.1, a surprisingly low value compared to Trans-1,3-dithiane 1,3-dioxide (24.9). While the deprotonation of 1,3-dithiolane and 1,3-dithiolane 1-oxide leads to unstable carbanions that cleave, the anion of Trans-1,3-dithiolane 1,3-dioxide has shown sufBcient stability to undergo addition reactions with aldehydes. Moreover, because of the Cj-symmetry incorporated into a five-membered ring, its potential to serve as a chiral acyl anion equivalent has been tested. 

Eor solubility reasons, a dual solvent system, i.e., THF/pyridine has to be used. Through variations in the metal counterion, reaction temperature, and the aldehyde used, it was shown that, contrary to Trans-1,3-dithiane 1,3-dioxide, best reactivities were obtained at low temperatures (—78 °C) with a lithium ion. Even at that temperature with a sodium ion, as demonstrated by scrambling experiments with aldehydes, equilibration begins to occur with a slow reverse reaction. Upon heating, the equilibration erodes the good initial kinetic ratio and diminishes the yield. To completely circumvent this, the authors used 2.4 equiv of LiHMDS at —78°C. This results in the formation of a bis-sulfinyl... 

---