Cyclopropanone dithioketals

A variety of cyclopropanone dithioketals have been prepared by the dehydrohalogenation of 3-halo dithioketals. 21,40,41) This method was... 

Table 6. Cyclopropanone dithioketals from base catalyzed cyclization of 3-halo-alkyl dithioketals...

Reductive Uthiation of dithioketah. Cyclopropanone dithioketals (1) are reduced by lithium naphthalenide to the sulfur-stabilized cyclopropyl anions 2 in quantitative yield. Lithium in HMPT is less effective. ... 

Cyclopropanone dithioketals. Methyllithium (1 equiv.) in combination with TMEDA (2 equiv.) is an excellent reagent for elimination of thiophenoxide from a l,l,3-tris(phenylthio)alkane to form cyclopropanone dithioketals (equation I). 

As mentioned above, one major drawback of the Trost methodology is its restriction to the parent compound. It was the Cohen group who found an alternative approach to phenylthiocyclopropyl lithium chemistry by using a reductive lithiation of readily accessible cyclopropanone dithioketals which also works for alkyl-substituted cyclopropanes. The anions obtained by reduction with two equivalents of lithium naphthalene or preferably lithium l-(dimethylamino)naphthalene (LDMAN) can effectively be trapped by apt electrophiles (equation 112). 

An allylidene cyclopropane synthesized via phenylthiocyclopropyl lithium has served as a potent diene in a Diels-Alder reaction. Earlier, several methods for ring-opening of cyclopropanone dithioketals—one leading to ketones (equation 115)—had been reported ... 

TABLE 18. Cyclopropanone dithioketals from l,l,3-tris(thiophenyl) alkanes and methyl lithium ... 

Tishchenko and coworkers obtained dihydrofuran derivatives when 2-benzoyl-1,1-dichlorocyclopropane (102) was treated with alkoxides (Scheme 40) . Product (107) is highly reminiscent of butenolide (70) obtained by the addition of chloromethoxycarbene to acrolein as discussed earlier (Scheme 29) and may result from ring-opening of cyclopropanone ketal (104). Perhaps a more likely mechanism involves addition of alkoxide to intermediate 103 followed by cyclization 106 - 107. When treated with thiophenoxide, 102 gave cyclopropanone dithioketal (108). A similar result has been obtained by Ban well (Scheme 41) . Treatment of 109 with thiophenoxide gave dithioketal 110 in 98 % yield. In contrast to the results of Tishchenko, however, keto ester products (112) were obtained from 2,2-dichloro-l-acylcyclopropanes (111) and alkoxides (Scheme 42) ... 

Lithium naphthalenide (2 equiv.) is a superior reagent for reductive lithiation of cyclopropanone dithioketals. The reaction is complete in THF at — 70° in less than 15 minutes. ... 

Cyclopropanation, 40, 172 Cyclopropanes, 420-421,453-454 Cyclopropanone dithioketals, 306 Cyclopropenation, 434-435 Cyclopropylacetic acid, 377 Cyclopropyl alcohols, 445 Cyclopropyl bromides, 291 Cyclopropylidenetriphenylphosphoiane, 339... 

Treatment of trithiane (73) with potassium amide (Table 17) gives spiro compound 74 in good yield Other dithioketal examples are shown. Cyclopropanone diselenoketals, i.e. 

When certain jS-keto-dithioesters (87) are treated with Grignard reagents, thiophilic addition occurs and 2-hydroxycyclopropanone dithioketals (88) are produced (Scheme 35) Only one isomer is obtained and a concerted cis-homo-l,4-addition has been proposed to account for the stereospecificity observed. Along somewhat similar lines, Giusti and coworkers have synthesized several cyclopropanone ketals by treating l,3-dibromo-2-propanone ketals with active metals (Table 20). Allenes are a byproduct in this reaction. Dihaloketals may also be cyclized electrolytically (Table 21). ... 

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