Tosylhydrazones cleavage

Titanium silicate molecular sieves not only catalyze the oxidation of C=C double bonds but can be successfully employed for the oxidative cleavage of carbon-nitrogen double bonds as well. Tosylhydrazones and imines are oxidized to their corresponding carbonyl compounds (243) (Scheme 19). Similarly, oximes can be cleaved to their corresponding carbonyl compounds (165). The conversion of cyclic dienes into hydroxyl ketones or lactones is a novel reaction reported by Kumar et al. (165) (Scheme 20). Thus, when cyclopentadienes, 1,3-cyclohexadiene, or furan is treated with aqueous H202 in acetone at reflux temperatures for 6 h in the presence of TS-1, the corresponding hydroxyl ketone or lactone is obtained in moderate to good yields (208). 

The 1,2-carbonyl transposition takes place through the enJo-epoxide 18 easily prepared through the tosylhydrazone 16, followed by regioselective cleavage to the less substituted double bond (17) with 2 equivalents of methyllithium [4] and epoxidation with MCPBA in chloroform from the more accesible convex face of the decalin system. 

A plausible reaction mechanism is that oxidative cleavage of tosylhydrazones is initiated by oxidation of the imino double bond of the tosylhydrazones with 51 to an oxaziri-dine derivative, which may be immediately converted to the carbonyl compound by a fragmentation reaction induced by 02 (equation 81). 

Oxidation of p-toluenesulfonylhydrazones.1 Carbonyl compounds can be regenerated in good yield from the tosylhydrazones by treatment with 1 equivalent of Tl(OAc), in HOAc. Room temperature suffices in the case of aldehydes, whereas reflux temperatures are used for ketones. The other product is T1(0S02C6H4CH3). This method is less useful for oxidative cleavage of semicarbazones long reflux periods are necessary, and acetoxylation is a side reaction. 

Oxidation of silyl tosylhydrazones (35) in an aprotic medium (dichloromethane) also results in the formation of nitriles, but in this case the conversion is apparently a true anodic process41 in which the key difference from the anodic behavior of oximes is the presence of the p-toluensulfonyl group, which facilitates cleavage of the N—N single bond (equation 20). 

Still other epoxide cleavage processes can be nucleophile induced, but without direct attack at a heterocyclic carbon. A good illustration of this phenomenon is seen in the alkylative elimination of epoxy tosylhydrazones (62). Optically pure allyl alcohols have been prepared... 

Scheme VIII/15. Cleavage of tosylhydrazones after N-bromosuccinimide treatment [43] [49].

Cleavage ofkeioximes. Ketoximes can be cleaved by aqueous bromine buffered with NaHCOs. Sodium hypobromite may be the actual reagent. The method can be used for cleavage of tosylhydrazones in this case yields are improved by added HMPT. ... 

Oxidative cleavage of hydrazones. Carbonyl compounds can be regenerated from 2,4-dinitrophenylhydrazones, tosylhydrazones, or N-methyl-N-tosylhydra-zones in 80-95% yield by oxidation with sodium nitrite in TFA or HOAc (0-5°, 1-2 hours). In the case of tosylhydrazones, the other product of cleavage has been identified as tosyl azide, the product of reaction of tosylhydrazine with nitrous acid. 

Direct transition from level 2 to level 0 can be achieved by way of the Wolff-Kishner reaction (treatment of the respective hydrazones with alkali), a classical pathway for the reduction of carbonyl compounds. At the same time, a direct conversion of aldehydes and ketones into alkenes is also feasible via reductive cleavage of their tosylhydrazones under the action of MeLi, the Shapiro reaction (Scheme 2.63). "... 

Cleavage of tosylhydrazones, arylhydrazones, and oximes to their parent ketones simply by exchange in acetone is said to offer a mild and convenient method under non-acidic conditions. Hexadeuterioacetone affords a-deuteriated ketones. Although tosylhydrazones of saturated ketones are reduced by borohydride in methanol to give hydrocarbons, similar treatment of the tosylhydrazone of cholest-4-en-3-one gave a mixture of 3a- and 3/S-methoxycholest-4-enes, apparently through a diazonium alkoxide ion pair. The reduction of tosylhydrazones of... 

Deprotection. Removal of the 2-naphthylmethyl group from 2-NpCH20R and oxidative cleavage of oximes and tosylhydrazones with DDQ proceed under mild conditions. Smooth and selective transformation of RNBn2 to RNHBn at room temperature by DDQ in dichloromethane containing some water is observed. ... 

Conversion of tosylhydrazones to ketones. Ketones can be recovered from the tosylhydrazones in 60-85% yield by treatment in CHCI3 with commercial bleach (5% NaOCl) for 5 min. The reaction gives low yields in the cleavage of tosylhydrazones of aldehydes. 

Cleavage of tosylhydrazones. Tosylhydrazones are cleaved to ketones in 85-95% yield by treatment with TiCls in dioxane and sodium acetate in 50% aqueous acetic acid at room temperature. ... 

The cleavage of an a.jS-epoxy-tosylhydrazone to give an acetylenic ketone has been employed to generate the 5(10)-seco-compound (386) best yields resulted from epoxidation of the tosylhydrazone of the 5(10)-en-6-one (385), rather than from first forming the epoxy-ketone. Aldol condensation of the derived saturated seco-3,10-dione (387) afforded the A-nor-B-homo-enone (388). The hydrazones derived from a, -epoxy-ketones and 2-phenyl- (389) or trans-23-diphenyl-l-aminoaziridines (390) undergo thermal fission (e.g. in refluxing DMF), also giving acetylenic aldehydes or ketones. ... 

Two papers report the synthesis of novel androstane derivatives methylated at C-8a. In the first" (Scheme 8). treatment of the tosylhydrazone of (143) with lithium hydride furnished the diene (144). Reaction with diborane. followed by alkaline hydrogen peroxide, gave the allylic alcohol (145), which was submitted to Simmons-Smith reaction and oxidized to the a-cyclopropyl ketone (146). Cleavage of the 7a.8a-methylene bridge with lithium in liquid ammonia afforded the 8a-methyl derivative (147). This was then converted into 17a-ethynyl-8a-methyltestosterone (148a) by a classical sequence of reactions. ... 

Oxidative cleavage of hydrazones. Dimethylhydrazones and tosylhydrazones are reductively cleaved to carbonyl compounds by either M0OCI3 or MoFo. Yields are generally in the range of 70-90%. Cf. Tungsten hexafluoride, this volume. 

Oxidative cleavage of hydrazones. This salt converts dimethylhydrazones or tosylhydrazones into the carbonyl compound under mild condilions (CHCla or Freon 113, 75-95% yield).i... 

Cleavage of a, -unsaturated p-tosyUiydrazones. Reaction of an a,)9-un-saliirated p-tosylhydrazone with sodium borohydride and methanol affords an allylic or benzylic methyl ether rather than a hydrocarbon as shown in the examples. Actually NaBH4 can be replaced by sodium methoxide or potassium carhoualc. The reaction is probably related to the Bamford-Stevens reaction. ... 

Oxidative cleavage of tosylhydrazones. This reaction can be carried out in a two-phase system (benzene or pentane-H20) with Na202. Yields of ketones are only about 70%. 

The epoxidation maybe avoided at aU by bromination of the tosylhydrazone with N-bromosuccinimide, followed by cleavage in weak base. The yield is then 80%. [180]... 

A soln. of cyclohexanone tosylhydrazone in acetone heated 24 hrs. at 65° in a sealed glass tube cyclohexanone. Y 78%. F. e., also cleavage of phenyl-, 2,4-dinitrophenyl-hydrazones, and oximes, and a-perdeuteriated ketones with acetone d(j, s. S. R. Maynez, L. Pelavin, and G. Erker, J. Org. Chem. 40, 3302 (1975). 

Cleavage of tosylhydrazones. A mixture of phenylacetone tosylhydrazone and Am-berlyst 15 in 10 1 acetone/water stirred at room temp, for 24 h phenylacetone. Y 91%. The method is applicable to aldehydes (especially in the presence of 10 eqs. of paraformaldehyde) as well as ketones it is simple and cheap furthermore, acid-sensitive groups such as furyl derivs., esters or ethers are not affected. F.e. incl. cleavage of oximes, 2,4-dinitrophenylhydrazones and semicarbazones, s. R. Ballini, M. Petrini, J. Chem. Soc. Perkin Trans. I 1988, 2563-5. 

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