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Allyl alcohols chlorochromate

Potassium nitrosodisulfonate, 258 Trimethylsilyl chlorochromate, 327 By hydrolysis of acetals or thioacetals Amberlyst ion-exchange resin, 152 Methylthiomethyl p-tolyl sulfone, 192 By isomerization of allylic alcohols N-Lithioethylenediamine, 157 By oxidation of aromatic side chains Trimethylsilyl chlorochromate, 327 From oxidative cleavage of alkenes [Bis(salicylidene-7-iminopropyl)-methylamine]cobalt(II)... [Pg.378]

The use of pyridinium-based chromium(vi) oxidising agents (cf. Section 5.7.1, p. 587) is illustrated by the use of the supported reagent, pyridinium chlorochromate-alumina, for the conversion of the cyclic allylic alcohol, carveol, into the corresponding oc,/ -unsaturated ketone, carvone125 (Expt 5.88). [Pg.607]

Although in principle naturally occurring (—)-galanthamine could have been prepared by an identical sequence of reactions commencing with D-tyrosine, an alternate route to 319, the enantiomer of 314, was developed. Thus, epimeriza-tion of the methyl ester group at C-6 of the A -trifluoroacetamide derived from 315 followed by oxidation of the allylic alcohol with pyridinium chlorochromate furnished 319 in 78% optical purity, albeit in low chemical yield. Since 319 could be converted to (-)-galanthamine (291) by the same sequence of reactions outlined for the transformation of 314 to (+)-galanthamine, its preparation may be considered to represent a formal total synthesis of 291 from L-tyrosine (163). [Pg.312]

The chroniium(VI) oxide-dipyridine complex also has beoi found to cause oxidative rearrangement of tertiary allylic alcohols to a,3-epoxy aldehydes and small amounts of a,3-unsaturated aldehydes (equation 6 and Table 3). This is potentially useful as a homologation sequence since the starting materials are readily available from vinyl metal addition to ketones. Use of pyridinium chlorochromate (PCC) for this transformation gives mosdy a,3 unsaturated aldehydes. [Pg.259]

Imidazolium dichromate is a selective oxidant for allylic and benzylic hydroxy groups. (Allylic alcohols are oxidized faster than benzylic alcohols.) The selectivity over saturate alcohols is similar to that of 4-(dimethylamino)pyridinium chlorochromate. DMF is recommended as the solvent for oxidations, since it appears that the choice of solvent is critical to obtaining high yields. This reagent has also been observed to cause some ( )/(Z)-isomerization during the oxidation of allylic alcohols. [Pg.278]

The tetraalkylammonium chromates prepared by Gelbard and coworkers a q)eared to be equally effective for all types of alcohols, but under the conditions of Santaniello et al., tetra-n-butylammonium chlorochromate was found to be a selective benzylic and allylic oxidant. It also efficiently converts aliphatic and aromatic thiols to disulfides. Trimethylammonium chlorochromate has also bera reported for the oxidation of allylic alcohols in DMF. ... [Pg.283]

With only minor modifications it is possible to prepare a selective oxidant for benzylic alcdiols benzyltiiethylammonium chlorochromate under phase transfer conditions exhibits such a preference. The preparation of benzyltiiethylammonium chlorochromate had been reported previously, but was initi ly assigned as the dichromate. It was demonstrated that this reagent (chromate or dichromate) shows good selectivity for benzylic and allylic alcohols, but unfortunately it was necessary to peifcwm the oxidation in HMPT. [Pg.283]

Pyridinium chlorochromate (PCC) Corey and Suggs prepared PCC by mixing CrOs with pyridine in HCl. PCC is used for the oxidation of primary and secondary alcohols in CH2CI2. This reagent is less efficient than Collins reagent for the oxidation of allyl alcohols. [Pg.271]

Not only allylic alcohols but also homoallylic alcohols can be epoxi-dized. A peculiar transannular oxidation takes place when 1-methyl-4-cycloocten-l-ol is treated with the Fieser reagent, [CrOj-(CH3C0>20-CH3C00H], or with pyridinium chlorochromate. Two dia-stereomeric keto oxides are formed in different ratios (equation 281) [535],... [Pg.154]

The allyl alcohol in the seven-membered ring is oxidized to the corresponding a,P-unsaturated ketone as expected, whereas the allyl alcohol in the five-membered ring is oxidized to afford the transposed a,P-unsaturated ketone after [3,3]-sigmatropic rearrangement. This behavior is only observed with cyclic, tertiary allyl alcohols upon treatment with one equivalent of pyridinium chlorochromate. The desired oxidation product 34 is obtained in 90 % over two steps. [Pg.108]

Acyloxy- and acylthiopyrazines are convenient acylation reagents for benzylamine, aniline, pyrrolidine, and related compounds (see Section 6.03.8.3). The acylthio compounds are also useful for acylation of alcohols and phenols. Pyrazinyl alkyl sulfoxides (see Section 6.03.8.4) give aldehydes and ketones by treatment with TFAA <91H(32)937>. The pyrazinium chlorochromate salt (181) is formed by addition of chromium(VI) oxide to a solution of pyrazine in hydrochloric acid, and it has proved to be more effective for the oxidation of aliphatic and allyl alcohols to the aldehydes than pcc <83H(20)2029>. [Pg.275]

Pyridinium Chlorochromate. The need for improved oxidation of primary alcohols and greater ease for isolation of products prompted further research into the nature of Cr(VI) reagents. Corey found that addition of pyridine to a solution of chromium trioxide in aqueous HCl allowed crystallization of a solid reagent characterized as 31, pyridinium chlorochromate (PCC). This reagent was superior for the conversion of primary alcohols to aldehydes in dichloromethane but less efficient than the Collins oxidation when applied to allylic alcohols. Oxidation of 1-heptanol with PCC in dichloromethane gave 78% of heptanal, for example. As stated by Corey, PCC is an effective oxidant in dichloromethane although aqueous chlorochromate species are not very effective oxidants. Oxidation of secondary alcohols to ketones is straightforward, as in Banwell s synthesis of y-lycorane, in which 32 was oxidized by PCC to the ketone (33). ... [Pg.200]

A useful application of chromium-based oxidants, especially pyridinium chlorochromate, is in the conversion of allylic tertiary alcohols to their transposed a,(3-unsaturated ketones. For example, treatment of the allylic alcohol 24 with PCC gave the a,p-unsaturated ketone 25 (6.23). The reaction is thought to proceed by rearrangement of the chromate ester of the allylic alcohol to give a new allyl chromate ester that is oxidized to the ketone. [Pg.381]

In order to remove the primary hydroxy group, the protected triol 24 was acet-ylated and treated with pyridinium tosylate to yield the monoester 25. Selective tosylation of the primary hydroxy group followed by Finkelstein exchange for iodine yielded the iodo derivative 26 which was transformed into the protected cyclohexene diol 27 by reductive removal of the iodine with tributyltin hydride followed by protection of the tertiary hydroxy group with dihydopyran. After removal of the benzoyl group by alkaline saponification the resulting allylic alcohol was oxidised to the desired enone 28 with pyridinium chlorochromate in buffered solution (ref. 16). [Pg.309]

Amongst the new deactivated chromium(VI) reagents which have been described are 3- and 4-carboxypyridinium dichromate, derived from nicotinic and isonicotinlc acid respectively, which oxidize benzylic and allylic alcohols, and a pyridinium chlorochromate-... [Pg.207]

Oxidation of the tertiary allylic alcohol with pyridinium chlorochromate (PCC) gave the unsaturated ketone. [Pg.93]


See other pages where Allyl alcohols chlorochromate is mentioned: [Pg.194]    [Pg.1514]    [Pg.438]    [Pg.62]    [Pg.1168]    [Pg.87]    [Pg.749]    [Pg.50]    [Pg.260]    [Pg.1716]    [Pg.470]    [Pg.1268]    [Pg.439]    [Pg.742]    [Pg.155]    [Pg.328]   
See also in sourсe #XX -- [ Pg.263 ]

See also in sourсe #XX -- [ Pg.263 ]

See also in sourсe #XX -- [ Pg.263 ]




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