Insertion of Carboryne into Aromatic Rings: Formation of Cyclooctatetraenocarboranes
摘要:
1-lodo-2-lithiocarborane is an efficient precursor to carboryne. It can react with arenes to give different types of dearomatization products, [4+2] cycloaddition and/or cycloinsertion products, dependent upon the substituents on the aromatic rings. The formal cycloinsertion products, cyclooctatetraenocarboranes, is generated from the [2+2] cycloaddition intermediates followed by thermal [3,3] sigmatropic rearrangement. This novel dearomatization of arenes with carboryne also serves as an important method for the synthesis of cyclooctatetraenocarboranes.
Carboryne (1,2-dehydro-o-carborane), in situ generated from the precursor 1-iodo-2-lithiocarborane, reacted with alkylbenzenes to give two regioisomers of the [4 + 2] cycloadducts as the major products in moderate to good yields, in which the steric factors play an important role in the regioselectivity. Minor products derived from benzylic C–H insertion reaction, annulation reaction, tandem [4 + 2]