Functionalization of Acetalic C(sp³)‐H Bonds by Scandium(III) Triflate‐Catalyzed Intramolecular Redox Reactions: Tandem 1,4‐Hydride Transfer/1,5‐Cyclization Processes Leading to Protected 1‐Indanones

Abstract

A new C À C bond forming reaction leading to adjacent quaternary carbons is reported. It is a one-pot hydride shift/cyclization process facilitated by the hydricity of the acetalic C À H bonds, with benzylidenemalonate fragments as electrophilic hydride acceptors, and the catalysis of scandiumA C H T U N G T R E N N U N G (III) triflate. The reaction products are 1,2-dihydroindane derivatives. Alkoxy and alkanethiolate groups can be also intramolecularly transferred from the acetalic carbon to the electrophilic benzylidenemalonate C=C bond.

CH Bond Functionalization through Intramolecular Hydride Transfer

“…Alajarin, Vidal, and co‐workers reported an interesting 1,4‐hydride shift/ring‐closure reaction in which (thio)acetals act as hydride donors (Scheme ) 92. Scandium triflate was identified as an efficient catalyst for these transformations.…”

The Redox‐Neutral Approach to CH Functionalization

“…Due to the hydrolysis of the acetal moiety in the strongly Lewis acidic medium, this reaction does not provide high chemical yields of product. This problem was solved by introduction of a 1,3‐dithiolane 17 , alleviating the issue of ketal hydrolysis 13…”

Recent Advances in the Synthesis of Indanes and Indenes

“…The tandem S N 2‐intramolecular MR was recently reported to afford 1,2,2‐trisubstituted indanes 39 from suitably functionalized benzyl chlorides 38 (Scheme ) . In another example, a one‐pot hydride shift/cyclization process, facilitated by the hydricity of acetalic C−H bonds, with benzylidenemalonate fragments as electrophilic hydride acceptors, and the catalysis of scandium(III) triflate, allowed the synthesis of protected 1‐indanone derivatives …”