Michael-type radical cyclization

Michael-type radical cyclization." A short synthesis of 3-demethoxyerythra-tidinone (3) involves a Michael-type radical addition. Thus 1 on reaction with BujSnH (AIBN) affords 2 as a single isomer in 65% yield. This product is converted by a three-step sequence into 3. 

A Favorskii-type rearrangement occurs on boron trifluoride promoted lead tetraacetate oxidation of enamines274 (Scheme 119). Five-membered rings may also be constructed by a Michael addition-radical cyclization process275 (Scheme 120). 

Conjugate addition of /3-ketoesters or 1,3-diketones to ethyl propynoate leads to Michael adducts of type 8 which undergo radical cyclizations to furans in the presence of 2,2 -azobisisobutyronitrile (AIBN)/tributyltinhydride... 

A key step in the synthesis of the simple aromatic bisphenol tetrangulol (3) by Brown and Thomson [18] was a Michael-type cyclization of a phenol to the chloronaphthoquinone moiety (Scheme 3). The starting material 8, connecting the naphthoquinone and the protected phenol, was prepared by an interesting radical alkylation of the chloronaphthoquinone 6 with a carboxylic acid 7 in the presence of silver ions and persulfate with concomitant decarboxylation (Torsell reaction [19]) to yield the dihydrobenzo[a]anthraquinone 9. The synthesis of tetrangulol (3) was concluded by dehydrogenation in boiling nitrobenzene. 

An intramolecular Michael-type 1-endo radical cyclization was reported by Kobayashi and coworkers [35] employing a trifluoromethyl substituted olefin as the internal radicophile. Thus, reaction of the iodide 123 with BuaSnH and AIBN furnished the 1-endo trig cyclized product 124 in 80% yield along with a minor amount of 6-exo trig cyclized product 125. 

Methods for the synthesis of central hydroisoquinolines or pyrrolo-hydroisoquinoHnes of manzamine A can be classified into 11 types of reactions (1) intermolecular Diels-Alder reaction, (2) intramolecular Diels-Alder reaction, (3) photochemical reaction, (4) radical reaction, (5) ionic cyclization, (6) intramolecular Michael reaction, (7) intramolecular Maimich reaction, (8) intramolecular [3 + 2] cycloaddition, (9) intermolecular [3 + 2] cycloaddition, (10) Pauson-Khand reaction, and (11) eneyne metathesis. 

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