Silanes iminium ions, addition

Upon addition of boron trifluoride etherate, acetoxylactam 8 eliminates an acetoxy group to produce A-acyliminium ion 9. The indo-lizidinone 10 is formed diastereomerically pure in an iminium-ion-ini bated cyclization reaction of the Overman type ending in a vinyl-silane.14... 

Step b Two acid-catalyzed cyclizations ally silane addition to an iminium ion followed by intramolecular imine alkylation and loss of MeOH. 

Somfai and Ahman have applied an intramolecular allyl silane addition to an AT-sulfonyl iminium ion as a key step in an alternative synthesis of (+)-anatoxin A [43]. Thus, L-pyroglutamic acid-derived compound 55 was homologated to aldehyde 126 and then to allyl silane 127 (Scheme 24). Using titanium tetrachloride, 127 could be cyclized in good yield to bicyclic olefin 128, which was converted to the alkaloid. 

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