The copper chelate catalyzed thermolysis of alkyl 2-diazo-3-oxobutyrate (1) and of 3-diazo-2,4-pentanedione (2) in the presence of several vinyl ethers to give 4-(alkoxycarbonyl)-and 4-acyl-2,3-dihydrofurans is used to probe the mechanism of this transformation in terms of the concerted 1,3-dipolar cycloaddition of the metaloxocarbene complex vs. the initial formation of the cyclopropane followed by 1,3 sigmatropic rearrangement to the heterocycle. Evidence is presented in favor of a third possibility, namely, that of a nonsynchronous stereospecific addition of the metal-carbene to the olefinic substrate to account for the formation of cyclopropanes, dihydrofiirans, and products of apparent allylic C-H insertion and cyclopropane structural isomerization from a common intermediate. This mechanism is supported by a study of the addition of lb to benzo[6]furan.The chemistry of photolytically and thermally generated a-ketocarbenes involves the processes of cyclopropane formation, insertion, rearrangement, and dimerization.1,2 The reactions of alleged metal-carbene complexes derived from reaction of an a-diazocarbonyl system with a transition-metal salt or chelate resemble those of the free carbene, which has given rise to such interpretations as singlet-like and triplet-like "carbenoid species".1 2*In addition to the usual cyclopropanes, such heterocyclic compounds as oxazoles,9"6 dioxoles,6® lactones,6b,c furans,7-10 and(1) (a) Kirmse, W. "Carbene Chemistry", 2nd ed; Academic Press:
This paper describes experiments on a low-pressure pneumatic actuator and load. An impulse test is described, in which the transient behaviour of a loaded actuator, operating in a particularly simple mode, was observed. The results are used to explain the nature of the expansion and compression processes in the actuator and to aid understanding of the effects of piston leakage and friction. Numerical values are obtained for the poly tropic gas constant and for the friction and piston leakage coefficients. The conclusions are shown to be relevant to an actuator operating in more complex modes and as a component of a pneumatic servomechanism.
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