Highly Regio- and Stereoselective [3+2] Cyclopentanone Annulation Using a 3-(Alkylthio)-2-siloxyallyl Cationic Species

Abstract

A new synthetic method for functionalized cyclopentanones was developed on the basis of a [3+2] cycloaddition reaction of a 1-(methylthio)-2-siloxyallyl cationic species and olefins. Allyl acetates 1a and 1b, which are the precursors of the allyl cationic species, are easily prepared in three or four steps from commercially available compounds. Under the influence of EtAlCl2 or AlCl3, 1a or 1b reacted with various kinds of olefins such as enol ethers, vinyl sulfides, styrenes, and trialkylolefins to afford the corresponding cyclopentanones in good yields. It is noteworthy that the sterically more hindered regioisomer was predominantly formed in every case. Furthermore, the reactions of 1b with vinyl sulfides exhibited surprisingly high stereoselectivity, which can be rationalized by the six-membered transition state models involving an orbital interaction between the sulfur atom of the vinyl sulfide and the α-carbon of the allyl cation.

(3+2)-Cycloaddition Reactions of Oxyallyl Cations

“…10 Although they are commonly utilized in (4+3) cycloadditions, Kuwajima demonstrated a highly regio- and stereoselective (3+2) cyclopentannulation by employing sulfur-substituted oxyallyl cations. 11,12 …”

Phosphine‐Catalyzed Rauhut–Currier Domino Reaction: A Facile Strategy for the Construction of Highly Functionalized Cyclopentene

“…Among this group of compounds, highly functionalized cyclopentenes are particularly important targets 2. Various methods, such as transition‐metal catalyzed,3 anionic,4 cationic,5 and free‐radical‐mediated [3+2] cycloaddition6 have been investigated. In recent years, phosphine‐catalyzed [3+2] cycloaddition, developed by Lu and Zhang in 1995,7 has inspired fruitful discoveries, especially for preparing various carbocycles and heterocycles 8.…”

Concise [4+3] cycloaddition reaction of pyrroles leading to tropinone derivatives

“…On the other hand, one of the authors reported the regio-and stereoselective [3+2] cycloaddition reactions using allyl acetates 1a and 1b as a three-carbon unit (Scheme 2). 9 Under the influence of EtAlCl 2 , allyl acetate 1 reacted with alkene 2 to afford cyclopentanone 3 in good yield. In this reaction, the methylthio group of 1 plays an important role in stabilizing the allyl cation species A as well as controlling the regio selectivity of the cycloadducts.…”