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Synthesis of functionalized 1-azaspirocyclic cyclopentanones using Bronsted acid or N-bromosuccinimide promoted ring expansions

TitleSynthesis of functionalized 1-azaspirocyclic cyclopentanones using Bronsted acid or N-bromosuccinimide promoted ring expansions
Publication TypeJournal Article
Year of Publication2004
AuthorsDake, GR, Fenster, MDB, Hurley, PB, Patrick, BO
JournalJournal of Organic Chemistry
Volume69
Pagination5668-5675
Date PublishedAug
Type of ArticleReview
ISBN Number0022-3263
Keywords1ST TOTAL-SYNTHESIS, ALPHA-HYDROXY IMINES, AMINO KETONE REARRANGEMENTS, CROSS-COUPLING, DIELS-ALDER REACTION, ENANTIOSELECTIVE, INITIATED PINACOL REARRANGEMENT, MARINE ALKALOIDS, PINNAIC ACID, REACTIONS, THERMAL REARRANGEMENT, TOTAL-SYNTHESIS
Abstract

Azaspirocyclic ring systems are present in a variety of alkaloids. Functionalized 1-azaspirocyclopentanones (6, 7, 11, 12) can be efficiently constructed through semipinacol ring expansion reactions of 2-(1-hydroxycyclobutyl)-p-toluenesulfonylenamides (4) promoted by either a Bronsted acid ((S)-(+)-10-camphorsulfonic acid or HCI) or N-bromosuccinimide, an electrophilic bromine source. Reactions promoted by N-bromosuccinimide tend to proceed in higher yields (80-95%) and with greater diastereoselectivity (3:1-1:0) compared to those reactions promoted by a Bronsted acid. In addition, N-bromosuccinimide promoted reactions can produce a complementary stereochemical outcome compared to the reactions using Bronsted acid.
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