Gold(I) carbene complexes of the type [Au(NHC)Cl], where NHC represents N-heterocyclic carbenes, have been synthesized. Two crystal structures of this type show that the molecules are stacked to form a linear polymer with Au‚‚‚Au interactions. Luminous [Au(NHC)(cbz)] (cbz ) carbazolate) were synthesized from [Au(NHC)Cl]. The crystal structure of one of this series indicates that the carbene and cbz rings are coplanar and two molecules are arranged pairwise in a head-to-tail fashion. While all the compounds prepared exhibit high-energy emission bands at ∼400 nm, [Au(NHC)Cl] complexes display additional low-energy emission bands at 580-650 nm, which are attributed to Au-centered transitions involving Au‚‚‚Au interactions. On the other hand, the low-energy emission bands of the [Au(NHC)(cbz)] complexes, which appear at 584-592 nm with fine structures, are likely to arise from the transitions involving mainly carbazolate tuned by Au, as also suggested by the density functional calculations. Crystal structures of Au(I)-dicarbenes are also reported.

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Two methods for stereoselective b-glycosylation of digitoxose were developed. The first achieved stereocontrol by a 1,3-participation of a N-methylurethane group under acid catalysis. The second utilized mercuric-ion catalyzed cleavage of thioglycosides and a 1,3-participation of ap-methoxybenzoyl group in a neutral medium. The first highly stereoselective and quite eficient synthesis of digitoxin (C7) was achieved by a combination of these methods. The furyl-substituted precursor IV of digitoxigenin (Scheme I) was used as aglycone, and the furan group was converted to the unsaturated lactone of digitoxin by our known oxidation procedure ( M -chloroperbenzoic acid/NaBH,) after the assembly of the carbohydrate portion of the molecule and its deblocking was completed.Introduction. -In previous communications of this series, we have described a novel and efficient methodology for the synthesis of cardenolides, bufadienolides and their analogues. As a result of this technique, we were able to synthesize up to now some 50

Abstract

(1978).A simple synthesis of the title compounds, which is more than 10 steps shorter and an order of magnitude more efficient than our recent photochemical synthesis of chasmanine, is described. The main feature of the new process is a stereo-and regiospecific addition of benzyl vinyl ether to a n o-quinone intermediate masked by a spirolactone group according to the method of Deslongchamps.KAHEL WIESNEK, THOMAS Y. R. TSAT et KKISHNAN P. NAMBIAR. Can. J. Chem. 56, 1451Chem. 56, (1978.On dkcrit une synthese simple des con>posds mentionnes dans le titre; cette synthese est 10 Ctapes plus courte et au moins 10 fois plus efficace que notre synthese photochimique que nous avons rkcemment rapportte pour la chasmanine. La pr~ncipale caracteristique du nouveau processus est une addition stCrCo-et regiospecifique de I'ether vinylbenzylique a un intermediaire o-quinone masque par un groupe spirolactone faisant appel a la methode d e Deslongchamps.[Traduit par le journal] , The construction of compound 2 was accon~plished by a modification of our photochemical method.In spite of the fact that the synthesis was stereospecific in all the steps and that all the substituents emerged in the correct positions siinultaneously with the construction of the polycyclic skeleton, it turned out t o be capable of considerable improvement. We have now developed a fundamentally different synthesis (see ref. 2 for model experiments) which is more than 10 steps shorter and an order of magnitude more efficient.This new process represents the final generation of our effort t o try out (with the aconite alkaloids) an 'engineering approach' (3) to the systematic development and simplification of synthetic strategy for polycyclic polysubstituted compounds.In the present communication we wish to disclose the direct synthesis of racemic 13-desoxydelphonine and a formal synthesis of chasmanine by the new method. The starting material was the aromatic intermediate 5 (mp 163-164°C) which was prepared from vanillin by the aziridine rearrangement method (cf. ref.3). The synthesis is fully stereo-and regiospecific and has been described in detail (4).A more efficient route to the same compound starting from o-cresol has also been developed. ' The aromatic rnethoxyl in compound 5 was selectively cleaved with sodium thioethoxide in dimethylformamide at 120°C for 1.5 h. The phenol 6 (mp