Allylic Mesitoates

To synthesize 1,5-dienes via cross-coupling reactions, the in situ reactions were studied of allylic mesitoates, allylic bromides and lithium in tetrahydrofuran at 0 C [20, 21]  

Substituents R as given above may vary from H and methyl to 4-methyl-pent-3-en-l-yl and 4,8-dimethylnona-3,7-dien-l-yl. Yields of such couplings could be as high as 95%. 

It was also found that the in situ generation of allylic organolithium compounds (this method avoids the necessity of synthesizing an allylic halide) in this manner can be used to produce allylic carbinols when aldehydes and ketones were present in the reaction mixture as electrophiles. 

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A selective synthesis of the otherwise difficultly accessible fra/w-alkenes is by treatment of the appropriate substituted allyl mesitoate with a Grignard reagent the latter does not react with the carbonyl group of the ester owing to steric hindrance, but instead acts as alkylating agent an example is the formation of trans-2-octene as follows 338... 

Katzenellenbogen, J. A., and R. S. Lenox The generation of allyllithium reagents by lithium-tetrahydrofuran reduction of allylic mesitoates. A new procedure for selective allylic cross coupling and allylcarbinol synthesis. J. Org. Chem. 38, 326—335 (1973). 

Trimethylbenzoate (Mesitoate) Ester 34. Methyl Carbonate 36. 2,2,2-Trichloroethyl Carbonate 39. Allyl Carbonate... 

Sodium salts of carboxylic acids, including hindered acids such as mesitoic, rapidly react with primary and secondary bromides and iodides at room temperature in dipolar aprotic solvents, especially HMPA, to give high yields of carboxylic esters.679 The mechanism is Sn2. Another method uses phase transfer catalysis.680 With this method good yields of esters have been obtained from primary, secondary, benzylic, allylic, and phenacyl halides.681 In another procedure, which is applicable to long-chain primary halides, the dry carboxylate salt and the halide, impregnated on alumina as a solid support, are subjected to irradiation by microwaves in a commercial microwave oven.682 In still another method, carboxylic acids... 

The reaction is useful only when the allyllithium is produced with a trapping agent in situ. The mesitoates may be prepared from allyl alcohols. 

Two similar approaches (Schemes 41 and 42) were described for the synthesis of racemic lactaral (19.1). Both converged to the preparation of the THP ether of lactarol (19.4), which was then converted easily into lactaral using standard methods. In the first of these syntheses (Scheme 41) 128) the mesitoate 26.139, prepared from diethyl furan-3,4-dicarboxylate by conventional steps, was coupled with the lithium derivative of the allylic bromide 26.140 to give 19.4, albeit in very low yield. A much more efficient synthesis of 19.4 162) was completed by coupling chloride 26.142 with the Grignard reagent 26.141 in the... 

A direct route to the many naturally occurring 1,5-diene systems is the coupling of two allyl units. To the available methods for this procedure can be added the reaction of an allylic halide with an allyl-lithium generated in situ by reduction of a mesitoate ester of the corresponding allylic alcohol (437). Only the mesitoate-derived allylic portion is subject to the allylic... 

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