Diallylation, regioselective

Very recently, Leitner has reported cationic nickel(n) catalyst systems for the cycloisomerization of diethyl diallyl malonate that shows high activities and regioselectivities for the formation of diethyl 3-methylene-4-methylcyclo-pentane-l,l-dicarboxylate with ee values up to 80% when using Wilke s azaphospholene ligand.355... 

Reaction of benzyl 4-O-benzyl-a-L-talopyranoside [142] and methyl 4,6-O-benzyli-dene-p-D-glucopyranoside [140] was less regioselective, giving 54% and 66%, respectively, of the 3-allyl ethers. No diallyl ethers were formed and no starting material remained, the rest being the isomeric 2-allyl ether. In both cases, tetrabutylammonium bromide was used to catalyze the reaction of the 2,3-O-dibutylstannylene intermediate with allyl bromide. 

The more reactive ft -carbon atom of ketone a,/ -dianions can be regiospecifically coupled with alkyl halides to give first lithium enolates, which are then trapped by more reactive carbon electrophiles such as allylic halides. The first example shown in Table 8 deals with the sequential /1-alkylation and ce-allylation of a ketone a,/1-dianion1 13. Thus, the dianion underwent regioselective alkylation at the ft carbon with //-pentyl bromide and then allylation with allyl bromide at the a carbon. When an excess of allyl bromide is reacted with the a, ft -dianion, the diallylated product is obtained in a good yield, whereas a threefold excess of pentyl bromide only resulted in the formation of the ft-alkylation product. Similar consecutive alkyl/allyl-type reactions are also possible for ketone a,5-dianions14. 

In another application, the totally regioselective direct anodic methoxylation of (45)-pyrimidinone-4-methyl carboxylate obtained from L-2,4-diamino butyric acid followed by diastereoselective substitution of the methoxy group by allyl trimethylsilane can be combined with the follow-up decarboxylative methoxylation of the carboxy function after hydrolysis. A second methoxy group exchange by allyl trimethylsilane yields the C2-sym-metrical (4i ,6i )-4,6-diallyl-pyrimidin-2-one enantiomerically pure [Eq. (50)] [246]. 

The E enols such as (367) obtained by photoenolisation of ortho-alkyl aromatic carbonyl compounds can be trapped by Diels Alder dienophiles and this has frequently been applied for synthetic purposes. A new example of this application has been published in which the ortho-methylbenzaldehydes (373) were irradiated in the presence of diallyl glutaconate (374) to give (375) as the products of regioselective Diels Alder trapping of the intermediate photoenol. ... 

This regioselectivity is reversed for olefins substituted with electron-releasing groups, and the 3-substituted pyridines are the predominant products. For example, reaction of 8 with allyl f-butyl ether gives 23 as the major product in 61% yield (Fig. 3.1). The 4-substituted pyridine 24 was isolated in 13% yield. The less-encumbered diallyl ether provided essentially the same ratio of 3- to 4-substituted pyridine products, indicating that this regiochemistry is in fact driven by electronic factors. 

In a formal synthesis of brefeldin A, treatment of the allyl propargyl ether 305 with the base n-BuLi promoted deprotonation a- to the alkyne, followed by rearrangement to give predominantly the homoallylic alcohol 306 (3.199). " Likewise, deprotonation and rearrangement of the macrocyclic substrate 307 promoted rearrangement to the homoallylic alcohol 308, used in a synthesis of the diterpene kallolide B (3.200). Regioselective deprotonation of the diallyl ether 309 and... 

In a novel carbon-carbon bond-forming reaction, catalysed by tetrakis(triphenylphosphine)palladium, allyl /8-keto-carboxylates are efficiently decarboxylated at room temperature to give y,5-olefinic ketones, alkylation taking place regioselectively at the carbon which originally bore the carboalkoxy-group e.g. Scheme 70). Diallylated by-products are observed in some cases. 

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