Alloc group protection-deprotection reactions

The reaction mechanism (Scheme 6.25) involves formation of a cationic 7t-allylpalladium complex by the oxidative addition of the substrate onto the catalyst. In case of a dimethylallyloxycarbonyl protecting group this step is disfavoured compared to Alloc and therefore the removal of dimethylallyl groups is slower or requires more catalyst. Accordingly, in homogeneous CH3CN/H2O solutions deprotection of (allyl)phenylacetate proceeded instantaneously with 2 mol % [Pd(OAc)2]/TPPTS while it took 85 min to remove the dimethylallyl group (cinnamyl is an intermediate case with 20 min required for complete deprotection). The reactivity differences are... 

Treatment with excess trifluoroacetic acid furnished the (dihydroiminoethano) carbazole 107 in 71% overall yield. Epoxidation of the alkene followed by a two-step protecting group modification gave epoxide 108, which underwent an oxidative epoxide opening followed by silyl protection to give silyl ether 109. Alloc deprotection, alkylation with (Z)-2-iodo-2-butenyl tosylate, followed by an intramolecular Heck reaction delivered pentacyclic diamine 110. A three-step formation of the p-ketoester 111 followed by a three-step reduction process afforded ester 112, which underwent a reduction and deprotection sequence to provide minfien-sine (99). A sequential catalytic asymmetric Heck-(V-acyliminium ion cyclization for the delivery of the enantiopure 3,4-dihydro-9a,4a-(iminoethano)-9//-carbazole is the highlight of the synthesis. 

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