Butatrien durch Thermolyse von Propiolsäure‐(2‐propinyl)ester

Abstract

SummaryFlow thermolysis of 2-propynyl propiolate (5) at 580" afforded butatriene (6) (ca. 50%) and, as by-products, 4-methylene-2-cyclobuten-1 -one (7), 2-ethynylpropenal (€9, l-penten-4-yn-3-one (9), 4-penten-2-ynal (10) (total ca. 10 %), along with some propynal, acetylene, CO, and CO. In the same way, propiolic acid (1,1-D2)-2-propynyl propiolate (11) led to (1,l-DJ-butatriene (12) and a little 4-((D,)rnethylene)-2-~yclobuten-1-one (13). A mechanism is proposed for the transformation of 5 into 6 and of 11 into 12, which also accounts for the formation of 7, 8, 9 and 10, as well as 13. The position of one of the published I3C-NMR signals of butatriene (6) must be revised. Thermolysis of methyl-(1) and ethyl propiolate (2) resulted in small yields of 2-buten-4-olide (3) and 2-penten-4-olide (4).Auf der Suche nach Analogien zur a-Alkinon-Cyclisierung (A + C) [ J befassten wir uns mit der thermischen Umlagerung von Propiolsaureestern (B + D) (Schema I ) .Wahrend aus Propiolsaure-methyl-(1) und -8thylester (2) bei 600", wie erwartet, Lactone 3 bzw. 4 (Schema 2), allerdings in nur 6% bzw. 8% Ausbeuten entstanden (s. IS. Oktoher, 1982.

Synthesis of Isobenzofuranones by Cobalt Catalyzed [2+2+2] Cycloaddition

“…General Procedure for Preparation of Substrates 1: Substrates 1a , 1d , and 1f‐I ,[12a], (general method below for 1e ) as well as 1b–c (general method below for 1c ) were prepared following previously reported procedures. The spectroscopic data are in agreement with the literature; 1a , 1b , 1d , 1g 1h …”

Pyrolytic decomposition of simple acetylenic esters

“…10 This led to the formation of butenolides by the process analogous to Route 4 in Scheme 3 above (Scheme 4). Under our conditions, which differ most especially in having a lower pressure and so favouring fragmentation processes, complete reaction of 7 required the higher temperature of 830 ˚C, and the main product trapped was acrolein 20 (15%) accompanied by low yields of formaldehyde and ethene.…”

A Practical Method for the Synthesis of 2-Alkynylpropenals

“…In connection with our studies on the total synthesis of glycinoeclepin A, we required a practical and efficient method for the preparation of α,β-unsaturated aldehydes of type 1 bearing alkynyl substituents at the C-2 position (“α-alkynyl acroleins”). Remarkably, only one example of the isolation and characterization of an aldehyde of this class has previously been reported in the literature , and also should be exceptionally prone to polymerization via radical pathways and in the presence of nucleophiles.…”