1.3- Dithianes addition reactions

The trimeric platinum(O) complex [Pt3(CNBu )6] undergoes a double oxidative addition reaction with 2,2-bis(disilanyl)dithiane to give tetrakis(organosilyl)bis(/-butylisocyanide)platinum(IV) complexes.53 The Si—Ge bonds in bis(silylgermyl)dithiane are also cleaved by [Pt3(CNBu )6] giving analogous platinum(IV) complexes with Pt—Si and Pt—Ge bonds.53... 

Nenajdenko et al. described the first example of addition of a 1,2-dication to C-C mutiple bonds. The only S-S dication found to participate in this reaction was the highly strained dication 115 derived from 1,4-dithiane. The reaction with alkenes 119 proceeded under mild conditions and led to derivatives of dithioniabicyclo[2.2.2]octane 120 as shown in Equation (33) and Table 21 <1998JOC2168>. This reaction was sensitive to steric factors and proceeded only with mono and 1,2-disubstituted ethylenes. Only alkenes conjugated with aromatic or cyclopropane moieties underwent this reaction. For the 1,2-disubstituted alkenes used in this study, the relative configuration of substitutents at the double bond was preserved and only one diastereomer was formed (see entries 2 and 3). 

Sulfonyl carbanions react readily with oxiranes, usually on the less hindered site With 2,3-disubstituted oxiranes, harsher conditions have to be used ° the addition of HMPA and/or BF3 Et20 can enhance the rate and the yield of the reaction, as in the case of lithiated dithianes. The reaction has been widely employed in organic... 

The diastereoselectivities in the nucleophilic addition reactions of l,3-dioxane-5-ones 37 and l,3-dithiane-5-ones 38 were studied by employing two newly available theoretical tools, the exterior frontier orbital electron (EFOE) density of the 7tc=o -orbitals and the 7t-plane-divided accessible space (PDAS) as quantitative measures of the 7t-facial steric effects <1999CRV1243, 1999CC621, 1999CL1161, 2000H(52)1435, 2001HAC358>. The two parameters predict correctly the experimentally observed stereochemical reversal of 37 and 38 (R = Ph see Table 1) in particular, the PDAS values for both substrates clearly show the opposite steric environment about the carbonyl carbon atom of these heterocyclic ketones and prove sizeable ground-state conformational differences to be responsible for the observed reversed facial stereoselection. 

CEJ1358> and the ruthenium mediated isomerization of double bonds (cf. Scheme 89, Section 8.11.7) <2007TL137> are recent examples of transition metal catalyzed manipulations at the side chain carbon atoms of 1,3-heterocycles. A novel side-chain addition reaction of aldehydes to 6-alkylidene-l,3-dioxin-4-ones was used for the construction of intermediates of lophotoxin <2006CJC1226>. An acid-catalyzed intramolecular cycloaddition of a hydroxy group to an alkene has been effected by the presence of an adjacent 1,3-dithiane moiety <2006TL4549>. 

Routes to benzo-fused derivatives of 1,4-dioxanes, 1,4-oxathianes and 1,4-dithianes make use of anions or dianions of the appropriate 1,2-disubstituted benzene. An alternative approach to the synthesis of 1,4-benzodioxanes involves Diels-Alder addition reactions of alkenes across the quinone function of 1,2-benzoquinones, e.g. (352) — (353). 

Stereoselective intramolecular conjugate addition reactions (Scheme 4) of dithiane anions tethered to an a,/ -unsaturated nitrile have been developed to advantage for the synthesis of axially substituted indolizidines and quinolizidines.81 The control of axial nitrile orientation by a peg-in-a-pocket template effect has been discussed. 

While such transition-state models have helped us to rationalize the patterns of selectivity observed in other reactions of 2-acyl- 1,3-dithiane 1-oxide substrates, such clear trends are not found in conjugate addition reactions (Table 3). One simple explanation for the poorer levels of stereoselectivity may be bond rotation within the acyl substituent, allowing the enone moiety to attain conformations other than those shown in 17 and 18. 

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... 

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. 

Acylsilanes. The reaction of anion (1) with alkyl halides generates a functionalized dithiane which, when hydrolyzed under mild conditions, provides the corresponding acylsilane (eq 16). More highly substituted acylsilanes have been accessed by initial formation of the dithiane from the aldehyde, followed by deprotonation and silylation with TMSCl (eq 17). Acylsilanes have been used as sterically hindered aldehyde equivalents forre-giocontrol in addition reactions (eq 18) and also as precursors for silyl-substituted vinyl triflates (eq 19). ... 

Some further studies on the preparation of antileukaemic lignans, e.g. ste-ganone, podorhizon, etc., have appeared. A simple one-pot route to these compounds involves a Michael addition reaction between aryl dithians and... 

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