Dithianes, oxidation

In the reaction of 1,3-dithiane oxide anions with iV-acylimidazoles the optimum procedure involved a sodium hexamethyldisilazide/butyllithium mixture as base [101]... 

There are no examples of reactions of substituents attatched to ring oxygen atoms. In the 1,3-dithiane-oxide series, however, Pummerer rearrangement of the sulfoxide moiety has been observed in both the mono- and disulfoxide systems (Equations (42)-(44)) <94CC1653,95S73>. 

Rearrangement of the bridgehead carbanion generated from a tied-back 1,2,4-trithiolane oxide has been shown to proceed via ring opening-ring closure, with formation of bicyclic 1,3-dithiane oxides in the presence of RI. ... 

The same preferences have been calculated315 and observed319 in the 1,2-dithiane oxide system. Although the chair forms are also more stable than the twist or boat in 1,3-, 1,4-dithianes and 1,3,5-trithianes, the preference of the oxygen is highly variable, depending on steric and electronic interactions. 

ABSTRACT Zeolite Y modified with chiral sulfoxides has been foimd catal rtically to dehydrate racemic butan-2-ol enantioselectively depending on the chiral modifier used. Zeolite Y modified with R-l,3-dithiane-1-oxide shows a higher selectivity towards conversion of S-butan-2-ol and the zeolite modified with S-2-phenyl-3-dithiane-1-oxide reacts preferentially with R-butan-2-ol. Zeolite Y modified with dithiane oxide demonstrates a significantly higher catalsdic activity when compared to the unmodified zeolite. Computational simulations are described and a model for the catalytic site is discussed. 

Reactivity of racemic hutan-2-ol over zeolite Y modified hy homochiral dithiane oxides. 

Fig. 2 Calculated low energy conformation of the protonated dithiane oxide cation (R=H) in zeohte Y (Si/Al = 1). The bottom view shows a view through the twelve ring containing e deprotonated framework oxygen, the top view is perpendicular to this. For clarity the zeolite framework is shown using a stick model and the adsorbed molecule is drawn in space filled form represented by tlie Van der Waals radii for the atoms being in the order S>0>C>H.

Fig. 3 Calculated low energy conformation of the protonated dithiane oxide cation (R=phenyl) in zeolite Y (Si/Al = 1). The views and presentational details are as for figure 2.

Figure 4 Calcxilated low energy conformations for enantiomers of < - — s butan-2-ol in dithiane oxide (R=H)...

Diethyl-3,5-octadiene 174 Dithiane oxides alkylation of 84 carbanions of 84 Dithianes alkylation of 76,79 as acyl anion equivalents 75 carbanions of 76,79 cleavage of 14-18.76,79 desulfurization of 78 oxidation of 23... 

Variation of 2-alkyl substituent exerted an effect upon diastereoselectivity. The best diastereoselection was obtained when incorporating a 2-ethyl substituent for acyl dithiane oxides (Table 3.6). The diastereoselectivity and the sense of induced stereochemistry can be rationalized on the basis of a simple chelation control model. 

As with our other acyl dithiane oxide systems, the thioacetal moiety can be readily removed by hydrolysis, in this case without affecting the dihydroisoxazoline ring (Scheme 11). 

While zeolites are themselves rarely chiral, adsorption of chiral inductors can enable enantioselective or diastereoselective reactions. For instance, Y zeolites have been modified with chiral dithiane oxides (47) Ramamurthy and his group have... 

Butyl-2-phenyl-l,3-dithianes and dithiane oxides have been synthesized with C, F, and labeling to act as probes of the GABA receptor complex <95JMC2663>. 

Alkylation and acylation of dithiane oxides are highly stereoselective processes. In such transformations, it is noticed that the anti substrate leads to the syn acyldithiane oxide (Scheme 4.55), with the choice of base being pivotal in the process. The use of butyllithium for acylation and sodium t-butoxide/butyllithium mixtures for alkylation with aldehydes tends to give the cleanest and most efficient reactions. Of late, simple 2-substituted dithiane oxides have been prepared with very high enantioselectivity, and such compounds have become the preferred starting materials for the various systems under scrutiny. 

Grignard reagents add efficiently to acyldithiane oxides to furnish tertiary alcohols in excellent yields and without loss of the dithiane oxide unit by nucleophihc displacement (Scheme 4.59) [112]. 

One-pot stereocontrolled cycloalkanone synthesis using dithiane oxides... 

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