A New Reaction Type in the Conversion of Enamines with 1,4‐Diphenyl‐2‐butene‐1,4‐dione to Give Cage Compounds

Abstract

Mn-N bond lengths (2.406(4) A). As expected with a higher coordination number, Mn to ligand bonds are considerable longer than those of six-coordinate Mn" complexes, but are similar to those found in the square-antiprismatic complex, [Mn(cyclen),12 + (2.384-2. 435 (cyclen = 1,4,7,10-tetraazacyclododecane). The only other examples of discrete bipyridine-N,N'-dioxide) and (Et,N),~(NCS),]. ["] The great flexibility of the [2. 6.872 A in the empty ~r y p t a n d . [~~~ The metal has induced a twisting of the ligand about the triad resulting in an oblique (ob) arrangement of the C3-C3' groups compared to the parallel (leg configuration of the cryptand and cryptates of larger cations. This creates a chiral dication which is isolated as a racemic mixture in a centrosymmetric space group. The large change in ligand conformation compared to the uncomplexed cryptand and lack of crystal field stabilization energy for a high-spin d5 Mn"suggests that there is little kinetic stability to this complex. Yet the complex is stable in anhydrous acetonitrile where its solution EPR spectrum is distinct from that of Mn(CF,SO,),A pure powder of 1 exhibits a broad signal at g = 2.03, although powder and orientated single-crystal samples of 1 in a diamagnetic matrix (1 YO in [Cd c [2.2.2]cryptand] (CF,S03),)1251 exhibit well-resolved multiline axial spectra with a small zero-field splitting, D = 220 gauss (Fig. 3). Experimental ProcedureThe triflate salt of 1 is isolated as colorless, analytically pure.'26' crystallographic q~ality.'~" hexagonal plates in 80% yield, by diffusing diethyl ether into an anhydrous acetonitrile solution of an equimolar mixture of Mn(CF,SO,), . 2CH,CN and the ligand under a dry, dinitrogen atmosphere. 3) the addition of radical^."^ Because C,, is a polyfunctional molecule, a myriad of products is formed after treatment with an excess of a reagent, for example a nucleophile.[61 It is impossible to isolate isomerically pure single compounds from such reaction mixtures. To control nucleophilic additions to only one double bond in C,, and to maximize the yield of the monoadducts, we titrated dilute solutions of C,, in toluene with tert-butyllithium and ethylmagnesium bromide. The concentrations of C,, , the monoaddition product, and higher addition products upon addition of the nucleophile was determined quantitatively by high-pressure liquid chromatography (HPLC). For this purpose the initially formed fullerides were protonated with methanolic HC1 to give C,,HtBu 1 and C,,HEt 2 (Scheme 1). In this way the formation of products and the consumption of C,, could be followed very closely from the calculated peak areas (Fig. 1). The UVjVIS spectrum of each peak was simultaneously recorded by means of diode array scans (200-500 nm) allowing the unambiguous assignment of the HPLC peaks to the compounds based on their optical spectra. Because other anionic nucleophiles like amides, hydrides, alkoxides, and thiolates react similarly with C,, this synthetic method should allow access to a large variety of monofuncti...

Cycloaddition Reactions of Enamines

“…Thus, it was shown that the interaction of cyclic enamines 21 a-d with dibenzoylacetylene 22 leads to the formation of bicyclic cyclobutene derivatives 23 a-d, which, except for 23 a, instantly isomerize to monocyclic 1,3-dienes 24 b-d (Scheme 7). [11] For further convenience of presenting the material, we depicted frequently used enamines in this review in Figure 2.…”