Esters Barbier syntheses with

Nakata utilised the Sml2-mediated Barbier-type cyclisation of a primary iodide with an ester as part of a convergent synthesis of trans-fused 6,6,6,6-tetracyclic ethers, which are typically found in marine polycyclic ethers.62 Treatment of iodide 50 with excess Sml2 in the presence of 1 mol% of Nil2 led to the smooth formation of intermediate hemiacetal 51, which was dehydrated to give dihy-dropyran 52 that was then further elaborated to give tetracycle 53 (Scheme 7.23).62... 

Nitriles and esters are also unreactive in Smh-promoted Barbier reactions. A very useful procedure for lactone synthesis has been developed making use of this fact. Treatment of 7-bromobutyrates or 8-bro-movalerates with Smh in THF/HMPA in the presence of aldehydes or ketones results in generation of lactones through a Barbier-type process (equations 25 and 26). This nicely complements the -metaUo ester or homoenolate chemistry of organosamarium(III) reagents described above (Section 1.9.2.1), and also the Reformatsky-type chemistry promoted by Sml2 (Section 1.9.2.3.2). Further, it provides perhaps the most convenient route to 7- and 8-carbanionic ester equivalents yet devised. 

The first enantiospecific total synthesis of (+)-ajmaline [(+)-17] was developed by Cook et al. 161). D-(+)-Tiyptophan methyl ester (126) was converted enantiospecifically, via intermediate 127, to the optically active )-N -benayltetracyclic ketone (-) 107, which was then transformed into the ot,P-unsaturated aldehyde (-)-128. When compound (-)-128 was stirred with 3-bromo-4-hq>tene in die Barbier Grignard process conditions the 1,4-addition products 129a,b... 

As mentioned in Sect. 2.3, Inanaga and co-workers have demonstrated that Barbier-type reactions of organic halides with carbonyl compounds are promoted by addition of HMPA [16]. They reported a mild convenient method for the direct synthesis of lactones from bromo esters and ketones or aldehydes by using a HMPA-promoted Barbier-type reaction with Sml2 (Scheme 13). They also found that the SmI2/THF-HMPA system was highly useful for the generation of... 

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