Thioketals amines

The reduction of a carbonyl group to an olefin has been accomplished by the Shapiro modification5 of the Bamford-Stevens reaction and by the hydride reduction of the corresponding enol ether,6 enol acetate,7 or en-amine.8 The nickel reduction of the thioketal has also been used successfully.9... 

The use of diphenylcyanomethylphosphine oxide is effective for the synthesis of ( )-a,3-unsaturated nitriles. ° Phosphine oxides can bis used to synthesize a variety of functionalized alkenes, including vinyl ethers (215 equation 51), ° vinyl sulfides (217 equation 52), ° allylic amines (219) and amides (equation 53), " ketene acetals (221 equation 54) and ketene thioketals (223 equation In the examples of a-thio substitution, the alkenes are formed directly. 

For synthesis of the trans N-Boc enantiomer 70, use was made of the chiral ketone 66, which is readily available by enzymatic resolution [91]. The ketone moiety was protected as the thioketal, and selective monohydrolysis then gave the monoacid 68. Curtius rearrangement of 68 with diphenylphosphorylazide (DPPA) and triethylamine (TEA) in tert-butanol gave the Boc-protected amine. Desulfurization with Raney nickel furnished the methyl ester 70 (Scheme 10). The (15,25) trans enantiomer was prepared analogously, starting from the enantiomer of ketone 66 [91]. 

DMP with high purity by the original procedure therefore, a few modifications have been suggested. In addition, DMP has been successfully used in the syntheses of polycyclic heterocyclesand in the removal of thioketals and thioacetals. It should be mentioned that other hypervalent iodine compounds can be used as oxidants as well, especially for the o-iodoxybenzoic acid (IBX), the precursor to DMP, which can oxidize tertiary cyclic allyl alcohol into O, y0-unsaturated cyclic ketones and secondary amines into imines and can convert epoxides or aziridines into corresponding of-hydroxy ketones or Q -amino ketones. 

Ar. ketals and thioketals, ar. and aliphatic epoxides, and ar. aziridines can be rapidly and conveniently reduced by alkali metals in liq. NHg. - E A soln. of 5 equivalents Na in liq. NHg added to a soln. of benzophenone ethylene ketal in ether, and the product isolated after 3 hrs. diphenylmethane. Y 94%. F. e., also alcohols from oxido comps., and amines from aziridines, as well as an anomalous aziridine reduction, s. E. M. Kaiser et al., J. Org. Chem. 36, 330 (1971). 

The nitroketone 118 (see Section IV,B,1) was treated with hydrogen chloride in ethanedithiol to afford the thioketal 119. Reduction of 119 with zinc and acetic acid and further treatment with Raney nickel in ethanol furnished lactam 120. Hydrolysis of 120 in aqueous methanol containing K2C03 gave 121, which on LAH reduction horded the amine 122. On treatment with sodium methoxide, the iV-chloro derivative of 122 gave verazine (123) (215). 

This transformation includes formation of cyclic acetals and ketals and, if R SH is used, thioacetals or thioketals. The R and R groups can be alkyl, hydrogen, or aryl. Imines are available from primary amines and enamines from secondary amines. Similarly, R and R can be hydrogen, alkyl, or aryl R is usually allyl or aryl. 

Carbonimidodithioates 1080, which can be regarded as thioketals of isocyanates, are easily prepared by reaction of primary amines or amino acid esters with CS2, followed by methylation with Mel. These compounds are converted into S-methyl-thiocarbamates 1081 in good yields upon treatment with ZnCh in MeCN/H20 (3 1) at 60 °C for 6-10 h. S-Methylthiocarbamates 1081 can also be conveniently prepared from 5,S-dimethyldithiocarbonate (DMDTC) 786, as described in Section 4.3.2 Carbamates . 

---