1.3- dithian-5-one

In the unsaturated series, ab initio calculations have been performed on 1,3-dithiin <90H(3i)70i>, and MM2 force field calculations have been applied to the 1,3-dioxin molecule <89JA6920>. The origins of stereoelectronic control in the carbonyl group reduction of l,3-dioxan-5-one and 1,3-dithian-5-one have been explored <92AG(E)1019>. 

A few studies of metal hydride additions are also available. Houk et al. briefly reported location of the transition-state structure for LiH addition to acetone (3-2IG) [145, 151]. Subsequently, alternative transition-state structures for addition of LiH to cyclohexanone, 3-fluorocyclohexanone, l,3-dioxan-5-one and 1,3-dithian-5-one were reported [147, 152, 153]. The general features of these cyclic transition states are similar to those of the analogous structures reviewed earlier. 

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. 

Methylenedithiol was used to construct cyclic meat flavor compounds, such as l,3-dithian-5-one 217 <1998FFJ177>. The reaction of the geminal dithiol with a 1,3-dibromide proceeds with pyridine as base in 44% yield (Equation 81). 

Photolysis of l,3-dithian-5-ones, for example, 360, and 3-methyl-5-thiacyclo-hex-2-ene-l-one, 361, gives 3-thietanones. A 3-thietanone intermediate was suggested in the photolysis of 3-thiatetralone. Photolysis of 8-thiabicyclo-[3.2.1.]-3-octene-2,6-dione gives a 3-thietanone, 8-thiabicyclo[4.1.1]-4-octene-3,7-dione. Thermolysis of the a-diazoketone 362 gives the 2-exomethylene derivative 363. ... 

Comparison of the O-C-O with the S-C-S anomeric interaction has been effected (2, 4 ) as shown in Scheme 2. In this case one can tell, unequivocally, that the O-C-O anomeric effect is the larger, for the overall AG° in the two systems is nearly the same and from the known conformational energies of 2-alkyl-l,3-dioxanes and -1,3-dithianes (5) it is obvious that the countervailing... 

The reaction of propargylic esters with aldehydes and hydrogen sulfide in the presence of boron trifluoride etherate leads to 1,3-dithiins (86) (Equation (56)) <71T5753>. Dieckmann cyclization of suitably substituted acyclic 1,3-dithioacetals gives rise to l,3-dithian-5-ones (87) (Equation (57)) <59LA(624)79, 63LA(661)84>. 

In contrast to 2-phenyl-l,3-dioxan-5-one, where nucleophiles add, regardless of their size, from the axial side of the carbonyl group, the same nucleophiles add to 2-phenyl-l,3-dithian-5-one exclusively from the equatorial side, to yield (165). A ring-expansion reaction has been observed when 2-methy 1-2-ethyl-1,3-dithiolan was brominated, giving the dithiin (166). ... 

Methoxytrimethylsilane, 123 Methyl acetoacetate, 92 Methyl bromoacetate, 107 Methyl 11-hydroxyundecanoate, 58 Methyl lithium, 27,28 Methyl 10-undecenoate, 58 2-Methyl-l, 3-dithiane, 81 (fl/ ,5 )-Methyl-3-phenyldiniethyl-silyl-3-phenylpropionic acid, 53-4 2-Methyl-3-Phenylprop-2-cnal, 111 2-Methyl 2-lrimethylsilyl-1,3-dithiane, 81 2-Methyl-l-(trimcthylsilyloxy)cyclo-hex-l-ene, 100,109 2-Melhyl-l-lrimethylsilyloxy)cyclo-hcx-6-enc, 100 2-Methyl-2-trimethylsilyloxy-pentan-3-one, 132 2-Methylacetophenone, 42-3 2-Methylbutyraldehyde, 85 2-Methylcyclohexanone, 99,100 2-Methylcyclohexanone, 131 4-Methyldec-4-ene, 67-8 Methylenation, 63 2-Methylpropen-l-ol, 131 Methyltriphenylphosphonium bromide, 27 Michael addition, 85 Monohydridosilanes, 128 Monohydroalumination, 29... 

In this chapter, the structures and chemistries of 1,3-dioxins, 1,3-oxathiins, and 1,3-dithiins are described, including both their fully saturated forms (1, 7, and 13) as well as their benzo analogs (6, 11, 12, and 17). The formally fully unsaturated monocyclic structures (4, 9, 10, and 16) contain only one endocyclic double bond with further unsaturation being accomodated by exocyclic double bonds (2, 3, 5, 8, 14, and 15), for example, by the introduction of a carbonyl group. Well known and intensively studied are the Meldrum s acid derivatives 18 and 19. In addition, 1,3-dioxane, 1,3-oxathiane, and 1,3-dithiane moieties can be part of spiro structures as well as hi- and tricyclic analogs. And finally, both the structures and chemistries of the corresponding sulfoxides and sulfones are also reported. 

Chemical shift trends for the remaining protons in the 1,3-series and related compounds can be deduced from the representative data given in Table 6. The rules outlined above also satisfactorily accommodate the data for methylene groups adjacent to just one heteroatom in the 1,3-dithiane the opposing effects of the j3 C—C and C—S bonds cancel whereas in the 1,3-dioxane the effect of the C—C and C—O bonds reinforce. At the C-5 methylene group, the axial proton is to lower field of the equatorial proton in the 1,3-dioxane and 1,3-oxathiane but to higher field in the 1,3-dithiane. +... 

Organotin 1,2-dithiolate complexes were featured in many studies the ligands used include aliphatic derivatives, e.g. ethane-1,2-dithiolate -SCH2CH2S-(EDT), -SCH2CHMeS-, alkenyl derivatives, e.g. -SCH=CHS-, maleonitriledithiolate (MNT), aryl derivatives, 1,2--SC6H4S (BDT) and toluene-3,4-dithiolate (TDT), as well as heterocyclic derivatives, l,3-dithiane-2-one-4,5-dithiolate (DMIO) and l,3-dithiane-2-thione-4,5-dithiolate (DMIT)191. 

The second synthesis of lasubine II (6) by Narasaka et al. utilizes stereoselective reduction of a /3-hydroxy ketone O-benzyl oxime with lithium aluminum hydride, yielding the corresponding syn-/3-amino alcohol (Scheme 5) 17, 18). The 1,3-dithiane derivative 45 of 3,4-dimethoxybenzaldehyde was converted to 46 in 64% yield via alkylation with 2-bromo-l,l-dimethoxyethane followed by acid hydrolysis. Treatment of the aldol, obtained from condensation of 46 with the kinetic lithium enolate of 5-hexen-2-one, with O-benzylhydroxylamine hy-... 

In our initial investigations,4,22 syn and anti 2-butyry 1-2-alkyl-1,3-dithiane 1-oxides were prepared by our standard means and were enolized using a suitable nonnucleophilic base (LHMDS) in THF at low temperature. The resulting enolate was subjected to alkylation with iodomethane, and the diastereoselectivities were determined by H NMR analysis of the crude product mixture. Our results are summarized in Scheme 5 and Table 4. Interestingly, the enolates were trapped as the corresponding silyl enol ethers, and NMR analysis revealed exclusive formation of one geometrical isomer, presumed to be the thermodynamically more favorable Z isomer.23... 

Although many workers have reported studies with 1,3-dithiane,3 7 no satisfactory description of its preparation has been published. Generally, 1,3-propanedithiol and formalde-hyde3,5,7 have been used as components in one instance, 1,3-dibromopropane was treated with sodium thiosulfate to form a precursor of the dithiol which was used as such with formalin.4 The formation of linear condensation products is a serious side reaction under such conditions. 

Unlike the carbanions from 1,3-dithians (see Chapter 3, p. 31 and Chapter 6, p. 90), the sulfinyl carbanions have the ability to undergo Michael additions (conjugate or 1,4-additions) with a,p-unsaturated carbonyl compounds. For instance, the secondary carbanion (44) from the ethyl ethylthiomethyl sulfoxide (45) may be sucessively reacted with ethyl iodide and 3-butene-2-one to give heptan-2,5-dione (46) via the tertiary carbanion (47), as shown in Scheme 23. The carbanion (47) may also be condensed with propyl bromide, and hydrolysis of the product yields ethyl propyl ketone (48) (Scheme 23). 

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