Deallylation

Deallylation of allylic compounds proceeds with liberation of rather stable carban-ions such as malonate anions. The deallylation can offer an opportunity to regard the allylic group as a protective group for acidic C-H bonds. Further synthetic utility of the deallylation is yet to be established. 

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Another method for deallylation of ally esters is the transfer of the allyl group to reactive nucleophiles. Amines such as morpholine are used[415-417], Potassium salts of higher carboxylic acids are used as an accepter of the allyl group[418]. The method is applied to the protection and deprotection of the acid function in rather unstable /f-lactam 664[419,420]. 

Hydrogenolysis of the diallyl alkylmalonate 757 with formic acid in boiling dioxane affords the monocarboxylic acid 758. Allyl ethyl malonates are converted into ethyl carboxylates[471]. The malonic allyl ester TV-allylimide 759 undergoes smooth deallylation in refluxing dioxane to give the simple imide 760(472]. The allyl cyanoacetate 761 undergoes smooth decarboxylation to give... 

The M-aUylated compounds may serve as precursors to the M-unsubstituted pyrrolidines by a mild Pd(0) catalyzed deallylation procedure [451. The deallylation may be more straightforward than hydrogenolysis of the M-benzylated product in which complications due to the presence of the oxime and the other Bn moiety (1,2 bond in the pyrrolidine ring) may arise during reduction. Attempts to prepare piperidine and azepine systems following the above procedure were unsuccessful. 

Immonium salts are sufficiently reactive to add organozinc halides in the absence of a catalyst.161 Diallylamines were used because of the ease of subsequent deallylation (see Section 3.5.2). 

Somewhat unexpectedly, monodemethylation of the esters (159 R=Me) proved impossible using several standard techniques. Deallylation of mono and diallyl ester analogues of (159), and of diallyl and allyl methyl [(1-acetyloxy)alkylJphosphonates was however acheived using palladium-containing catalysts, suggesting a potential wider applicability of the diallyloxy-phosphinyl group in synthesis. 

Having established that the inherent selectivity of the Heck reaction would not readily allow us to access aldehyde products related to the Wieland-Gumlich aldehyde, we considered a number of other possible reaction manifolds for C20-C15 bond formation. Each substrate was accessed by deallylation of cycloadduct 104 followed by alkylation with the appropriate allylic or propargylic halide. Inspired by the extensive studies of Bonjoch, Bosch, Sole, and co-workers,... 

In an analogous fashion to the reductive deprotection of allyl alcohols and allyl esters, the deallylation of allylamines is also possible (Eq. 337).270... 

Compound 10 was converted into allyl glycoside 11 in 73 yield in two steps, (a) Bu2Sn0CH2CH=CH2—SnCl,(4), and (b) MeONa—MeOH. Treatment of 11 with dimethoxypropane and TsOH, and then with benzyl bromide— NaH—DMF afforded compound 12 in 51% yield. Solvolysis of compound 12 in MeOH—AcOH, and then monobenzylation by the stannylation— alkylation method(5) gave the desired glycosyl acceptor 8 in 67% yield. Acetylation of compound 8 and then deallylation with PdCl2— AcONa in aq.AcOH(6) afforded a 93% yield of hemiacetal 13, which was treated with (a) SOCI2—DMF in dichloroethane(7) and (b) AgF— CH CN(8) to give the desired fluoride 9 in 73% overall yield. 

Conversion of the glucohexaosyl derivative 7 into the desired key intermediate 6 is shown in Scheme 6. Treatment of 7 with (a) NaOMe— MeOH, (b) (C1CH2C0)20—pyridine afforded in 70% yield the monoohloroacetyl derivative 21, which was deallylated with PdCl2— NaOAc—aq.AcOH to give the hemiacetal 22 in 60% yield. The transformation of 22 into fluoride 23 was achieved in 73% yield in 2 steps (a) SOClj—DMF and AgF—CH CN. Compound 23 was deacylated... 

A similar process can be efficiently used for the deallylation or debenzylation of the corresponding ethers 52 and 53, just using water as the quenching reagent after the lithiation process. Some examples giving alcohols or phenols 54 are included in Scheme 17 . 

Deallylation of 29 was achieved using 10% Pd/C in the presence of ethanolamine in refluxing ethanol to afford 30 in 77% yield (with 4% of the regioisomer). The reaction... 

The 4-amino group of 31 was selectively acetylated under acidic conditions using acetic anhydride (1 equiv.) and methanesulfonic acid (1 equiv.) in acetic acid and f-butylmethyl ether to give 32. Deallylation of 32 using 10% Pd/C in the presence of ethanolamine in refluxing ethanol proceeded as before to afford 1, which was converted to the phosphate salt in 70% yield with high purity (99.7%). The overall yield of 1 from epoxide 23 was 35-38%. 

Treatment of some mesylated N,N-diallylamino sugars with triethylamine tnhydrofluoride results m the fluorination and regioselective transfer of the mtro gen atom to give, after platinum-catalyzed reductive deallylation, 2,3-ammo-fluorodeoxysugars A mechanism involving aziridimum ions has been proposed [44] (equation 32)... 

The benzylidene derivative (94) has been converted into the alcohol (95) [97, 98] using the diborane — trimethylamine — aluminium chloride reagent [99] and into the diol (96) [95, 100, 101]. Veyrieres has converted methyl P-lactoside (and the corresponding allyl lactoside) into the 3-O-allyl ether (97) in good yield [102] by alkylation of the dibutylstannylene derivative in the presence of tetrabutylammonium iodide [103, 104], and this was converted into the alcohol (98) and the triol (99) [105]. Veyrieres [106] has also converted (97) into the per-p-bromobenzyl derivative and deallyl-ated the product to give a derivative with a free 3 -hydroxyl group. The diol (100) [107] has been converted by the stannylation procedure [108, 109] into the alcohol (101) [110, 111]. The partially acetylated benzyl P-lactoside (103) [101,112, 113] has been converted into the alcohol (104) via the orthoacetate [113]. 

The methyl 3 -0-allyl-P-lactoside (97) prepared by Veyrieres by the allylation of the dibutylstannylene derivative in the presence of tetrabutylammonium bromide [102] was converted into the per-p-bromobenzyl ether and deallylated to give (306). This was condensed "[106] with the chloride (282) in the presence of silver triflate to give a tetrasaccharide in 68 % yield. This was far superior to the condensation of the oxazoline (294) with (306) which gave a very low yield (9%) of tetrasaccharide. Depro-... 

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