Transannular acid-induced

Bicyclic 3a//-cyclopentene[8 annulcnc-l,4-(5//,9a//)-dioncs undergo three types of acid-induced transannular reactions (1) Michael addition (5-exo-trig or 6-exo-trig) leading to the tetracyclic diones, (2) 3 + 2-cycloaddition followed by a novel sequential skeletal rearrangement to 2-naphthalenone derivatives, (3) ipso-Friedel-Crafts alkylation accompanied by the rearomatization and the loss of water (Scheme 25). The factors that control the reaction mode of these transannular cyclizations are discussed... 

The conventional acid-induced transannular cychzation of 1,10-epoxy-costunolide, via carbocationic chemistry, results in a eudesmanohde mix-... 

Adio AM (2009) Germacrenes A-E and related compounds thermal, photochemical and acid induced transannular cyclizations. Tetrahedron 65 1533—1552... 

Attempts to induce transannular bonding in 1,5-cyclooctadiene monoepoxide have been moderately successful, but under acidic conditions only.91,92 ... 

Lewis acid-induced ring-opening of 80 provided a synthesis of a [4.4.1] oxa-bicyclic system, Eq. 61 [88]. The product arises via a transannular nucleophilic opening by an internal epoxide. 

Further transannular cyclization studies start from (E)- or(Z)-5-cyclodecenone while radical-induced reactions form hydroazulene skeletons predominantly, the acid-catalyzed reactions generate hydronaphthalene systems. Only 1,6-cyclization products are observed, the L -config-urated cyclodecenone leads to the tram, while the Z-configurated material yields the cis ring... 

Transannular cyclization can be induced by acid-mediated activation of a,/J-unsaturated carbonyl groups. Treatment of an a./J-unsaturated ketone with formic acid/boron trifluoridc-di-ethyl ether complex produces the tricycle 1423. Ketone 14 is a precursor in the pentalene 8 synthesis (Prins reaction analog). Transannular Prins cyclizations are described in Section 1.5.5.2.2.2.26-27. 

The bicyclo[3,3,0]octenol (78) is produced by a transannular cyclization of cyclo-octa-1,5-diene induced by thallium(lll) trifluoroacetate, and Joulain and Rouessac have found that the fused 5,5-system (80) is produced when the bis-alcohol (79) is treated with perchloric acid in nitropropane. ... 

The second one-pot cascade reaction was used to complete the synthesis of the natural product from acid 69. Reduction of the two azide groups of 69 produced the highly polar diamine 70, which was treated with EDC and HOBt to induce an intramolecular lactam cyclization and deliver the macro-palau amine 71. When the crude reaction mixture of 71 was heated in TEA, compound 72, proceeding through amidine tautomer 71, elicited the key transannular cyclization and delivered the palau amine in 17% overall yield from 69. The outcome stereochemistry was all in the control of the stereocenters within the substrate. 

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