Hetero -cycloaddition-allylboration

Three-component Hetero-[4+2]-cycloaddition-Allylboration Tandem Reaction... 

Scheme 12.20. Synthesis of (5R,6S)-6-acetoxy-5-hexadecanolide using a three-component hetero[4+2] cycloaddition/ allylboration, by Gao and Hall [63]. Ac = acetyl, pin = pinacolato, Ms = methanesulfonyl, mCPBA = m-chloroperoxybenzoic acid.

Following this route, the authors achieved the synthesis of 10 analogues of compound 58, in a high global yield, where the crucial step of this total synthesis was the efficient catalytic enantio-, regio-, EIZ-, and diastereoselective three-component inverse electron demand hetero-[4+2] cycloaddition/allylboration sequence. This key process provides a rare example of an enantioselective hetero-Diels-Alder reaction involving acyclic 2-substituted enol ethers. Additionally, these compounds were evaluated for antimicrobial activity, and two of them showed more activity than the original thiomarinol H. 

B. Carboni, L. Toupet, G. Dujardin, Chem. Commun. 2003, 276-277. A novel diastereoseleetive route to a-hydroxyalkyl dihydropyrans using an hetero Diels-Alder/allylboration sequence, (h) B. B. Toure, D. G. Hall, Angew. Chem. Int. Ed. 2004, 43, 2001-2004. Three-component sequential aza[4+2] cycloaddition/allylboration/retro-sulfinyl-ene reaetion a new stereocontrolled entry to palustrine alkaloids and other 2,6-disubstituted piperidines, (i) B. B. Toure, D. G. Hall, J. Org. Chem. 2004, 69, 8429-8436. Design of a nonreductive method for chemoselective cleavage of hydrazines in the presence of unsaturations application to a steieoconveigent three-component synthesis of (-)-methyl palustramate. 

X. Gao, D. G. Hall, M. Deligny, A. Favre, F. Carreaux, B. Carboni, Chem.-Eur. J. 2006, 12, 3132-3142. Catalytic enan-tioselective three-component hetero-[4+2] cycloaddition/ allylboration approach to a-hydroxyaUcyl pyrans scope, limitations, and mechanistic proposal. 

Scheme9.37 Asymmetric synthesis of a-hydroxylated dihydropyrans via a catalytic hetero-Diels-Alder cycloaddition/allylboration sequence.

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