PTC in the Polyenolate-Mediated [10+2]-Cycloaddition for the Synthesis of α,α-Disubstituted Amino Acid Precursors

The manuscript describes a formal [10+2] higher-order cycloaddition between 2-arylideneindan-1-ones and α-alkylidene azlactones as higherene precursors and higherenofiles respectively. The reaction is realized under Brønsted-base catalysis utilizing the phase transfer catalysis approach. The key intermediate is an isobenzofulvene-derived polyenolate which acts as a 10-electron component in the higher-order cycloaddition. By using this strategy, a series of structurally diverse compounds containing a polycyclic hydrocarbon scaffold was prepared in 79–99% yields. In addition, the potential of the obtained [10+2]-cycloadducts has been confirmed by transformations, including the synthesis of a highly-valuable α,α-disubstituted N-protected α-aminoester.