From 1,3-Dithianes

To a solution of 2-methyl-l,3-dithiane (34.1 mmol) in THF (150 ml), cooled to — 30 °C, was added n-BuLi (34.1 mmol, 1.5 m in hexane) dropwise (3-5 ml/min). The resulting solution was stirred at —30 to — 20 °C for 1.5 h, and then TMSC1 (37.1 mmol) was added dropwise. After 2.5 h at — 25 °C, water (15 ml) was added, then most of the THF was removed in vacuo. Water and pentane were added, the layers were separated, and the aqueous layer was extracted thoroughly with pentane. The combined organic layers were washed with water, aqueous KOH (10%) and water, and dried. Concentration and distillation gave 2-methyl-2-trimethylsilyl-l,3-dithiane (26.8 mmol, 78%), b.p. 102°C/9.5mmHg. 

All of the following operations were carried out with the exclusion of light. 

A mixture of 2-methyl-2-trimethylsilyl-l,3-dithiane (121 mmol), mercury(n) chloride (266mmol), and mercury(n) oxide (181 mmol) in methanol (225 ml) and water (25 ml) was stirred vigorously and heated under reflux for 2 h. It was then cooled and filtered, and the precipitate was 

Higher hydrolysis yields can be attained using aqueous DMSO and mercury(u) chloride and cadmium carbonate (J). 

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Intermediate 10 must now be molded into a form suitable for coupling with the anion derived from dithiane 9. To this end, a che-moselective reduction of the benzyl ester grouping in 10 with excess sodium borohydride in methanol takes place smoothly and provides primary alcohol 14. Treatment of 14 with methanesulfonyl chloride and triethylamine affords a primary mesylate which is subsequently converted into iodide 15 with sodium iodide in acetone. Exposure of 15 to tert-butyldimethylsilyl chloride and triethylamine accomplishes protection of the /Mactam nitrogen and leads to the formation of 8. Starting from L-aspartic acid (12), the overall yield of 8 is approximately 50%, and it is noteworthy that this reaction sequence can be performed on a molar scale. 

The lithium salt of the stabilized anion derived from dithiane also provides displacement of halogen at phosphorus for the generation of species readily converted into additional functionalized organo-phosphorus compounds.69 The resultant materials are suitable for a wide range of applications, both as final products and as reagents for additional transformations. 

In connection with carbohydrates, (1,5,3,5,5W)-1,3-dimcthyl-2,9-dioxabicyclo 3.3.11 nonane has been prepared from dithiane and D-glucose263. An epoxide derived from D-xylose 195 has been opened regioselectively by means of compound 161 at the 4-position in 90% yield264. In the case of the methyl 2,3-anhydro-a-D-lyxofuranoside 196 the ring... 

The anions derived from dithianes react with alkyl halides to give the corresponding alkylated dithianes. Their treatment with HgCl2-HgO regenerates aldehydes or ketones, respectively, as depicted below. 

Acyl-lithiums and their Equivalents. Details have appeared of the preparation of di-isopropylcarbamoyl-lithium (LiCONPr a) by reaction of di-isopropylformamide with t-butyl-lithium. Lithiated dithioacetals, particularly those derived from dithians, continue to be popular. Alkylations of such species have been important reactions in syntheses of 25-hydroxycholesterol, pyrenophorin and vermiculin," and several chain-elongated sugars. 2-(3,3-Dialkoxypropyl)-l,3-dithians may be converted via their lithiated derivatives into protected 2-hydroxycycIobutanone derivatives (Scheme 1), themselves potential synthons for 1,4-diketones and cyclopentenones. ... 

Over the last two decades, 1,3-dithianes have become ubiquitous as acyl anion equivalents in organic synthesis, with thioacetal chemistry having already been well established [107]. It is therefore somewhat surprising to find that 2-acyl-l,3-dithianes, which may easily be prepared in excellent yield from dithiane 2-anions, have received relatively little attention [108]. The development of 2-acyl-l,3-... 

Keten dithioacetals are versatile intermediates for ketone synthesis. Their preparation by the condensation of ketones with the lithium derivatives of bis(phenylthio)methylboronates (25) and from dithians have been reported... 

A synthesis of A- -cyclopentenones from 1,3-dienes has been developed by Corey" (Scheme 11). This is exemplified by Diels-Alder type addition of isoprene to (315) (from dithian and trityl fluoroborate) to give adduct (316) in 95% yield. On treatment with 1 equivalent of n-butyl-lithium at — 78°C in THF, (316) formed ylide (317) which, following attainment of room temperature and evaporative distillation at 80 °C, gave the rearranged product (318) in a yield of 96%. This vinylcyclopropane underwent rearrangement at 200 °C in benzene for 4 h to give (319), in 97 % yield the thioketal was readily converted into (320). The same reaction sequence was successfully applied to prepare both (321) and (322). 

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