Uncatalyzed, Solvent-Free [2+2] Cycloaddition of Cyclic Ketene Trimethylsilyl Acetals with Electrophilic Acetylenes

Abstract

Cyclic ketene trimethylsilyl acetals reacted with electrophilic acetylenes (ethyl propynoate, dimethyl acetylenedicarboxylate and ethynyl methyl ketone) to afford the corresponding [2+2] cycloadducts. The reactions were run at room temperature, without a catalyst and under solvent-free conditions. Scheme 1. [2ϩ2] Cycloaddition without activation and with activation [a][a] Chromatography on silica gel was not necessary in this case.Scheme 5. Stereoselective [2ϩ2] cycloaddition of 23 with EP (1) and DMAD (5) Scheme 6. [2ϩ2] Cycloaddition of enamine 26 with EP (1) and DMAD (5) Eur.

Solvent‐Free and Catalysts‐Free Chemistry: A Benign Pathway to Sustainability

“…Miesch and Wendling [97] reported one-pot nonphotochemical [2 + 2] cycloadditions at room temperature between readily available cyclic ketene trimethylsilyl and electrophilic acetylenes (Scheme 33) using CCl 4 /ZrCl 4 and CCl 4 under SF-CF con-Scheme 29. CDI-mediated amide synthesis through ball milling under SF-CF conditions.…”

Total Synthesis of Viridiofungins A and B

“…After testing a number of catalysts, OCM between alkene 3 and the side chain alkene 4 was best achieved using Grubbs− Hoveyda catalyst 15 (12) to afford the desired labile product 13, but this was contaminated by a very similar inseparable byproduct which could only be detected by the presence of some doubled signals in the 13 C NMR spectrum along with the OCM homodimer derived from 4 (Scheme 4). Similar results were obtained using the dimer 9a derived from alkene 4 as the OCM partner.…”

“…Deprotection of the mixture of 16 and the byproduct with formic acid and purification by RP-HPLC allowed for the of the two products (Scheme 5). One was identified as viridiofungin B (2), while the other product possessed one less methylene unit as judged by mass spectrometry and 13 C NMR spectroscopy (one less methylene signal in the 29−30 ppm region). This compound was therefore assigned as the desmethylene analogue 17.…”

“…The synthesis of the bicyclic lactone 6 is summarized in Scheme and begins with lactone 7 , obtained by protection of ( S )-(+)-γ-hydroxymethyl-γ-butyrolactone . A formal [2 + 2]-cycloaddition , between the silylketene acetal derived from 7 and di- t -butylacetylene dicarboxylate ( 8 ) gave the cyclobutene diester 9 in good yield and high stereoselectivity. HF•pyridine-induced deprotection, concomitant oxa -Michael reaction, and intramolecular cyclobutanone ring opening , gives the bicyclic lactone 6 .…”

Total Synthesis of (+)-Trachyspic Acid 19-n-Butyl Ester

“…Aldehyde 3 could originate from the cascade rearrangement of the cyclobutene diester 5 followed by orthogonal ester protection. Cyclobutene 5 can be accessed by a formal [2 + 2]-cycloaddition , between acetylene diester 7 and the silylketene acetal derived from known lactone 6 , available by silylation of commercially available ( S )-(+)-γ-hydroxymethyl-γ-butyrolactone.…”