N,N‐Bis(trimethylsilyl)ynamines: Cycloaddition Reactions with Dimethyl Acetylenedicarboxylate and Ketenes

Abstract

N,N-Bis(trimethylsily1)ynamines 1 react with dimethyl acetylenedicarboxylate (2) in a molar ratio of 1 :2 to afford 3-cyclopropenylfurans 3. Configuration and conformation of 3a are confirmed by X-ray crystallography. Addition of a further mol of 1 furnishes the fumarates 4. With ketenes 5 (512, d are prepared in situ) a competition between the formation of cyclic butenone derivatives 6 and allenic imidates 7 is observed, depending on the substitution pattern of 1. After hydrolytic Ynamines are very useful building blocks in organic synthesis [']. However, until recently their use was limited with respect to the substitution pattern at the nitrogen atom, since only tertiary ynamines areThe synthesis of MN-bis(trimethylsily1)ynamines 1 as synthetic equivalents of primary ynamines was reported recently by our labIn the course of subsequent work concerning the nucleophilic reactivity of the bissilylated nitrogen atom it became evident, that the ynamines 1 show only very limited reactivity at nitrogen. In all cases studied, conjugate addition to the triple bond by electrophiles was ob~erved [~,~].In this paper, we report on our results of addition reactions of dimethyl acetylenedicarboxylate (2) and ketenes 5 to the triple bonds of 1. We use the relatively easily accessible n-butyl-and phenyl-substituted compounds la,b as examples for other aliphatically and aromatically substituted derivatives of 1. We are particularly interested in the chemical reactivity of the N,N-bissilylated ynamines 1 in comparison with those of known N,N-dialkyl derivatives. Furthermore, these experiments are aimed at the synthesis of cycloadducts of ynamines possessing primary amine functionalities after hydrolytic cleavage of the N-Si bonds. Reactions of the Ynamines 1 with Dimethyl Acetylenedicarboxylate (2)Reports on reactions of ynamines with electron-poor alkynes areFicini and Barbara describe the cycloaddition of one mol equivalent of ynamine to two equivalents of dimethyl acetylenedicarboxylate (2) forming a persubstituted anilineThe reaction of the N,N-bis(trimethylsi1yl)ynamines 1 with two mol equivalents of 2 takes a completely different workup, the corresponding amides 10 or the vinylogous amides 9 are obtained in good yield. These experiments indicate that the silylated ynamines 1 show a completely different, more selective reactivity towards dimethyl acetylenedicarboxylate compared to N,N-dialkyl-substituted ynamines, yielding furan derivatives instead of anilines. Towards ketenes, however, a similar cycloaddition reactivity as for N,N-dialkylynamines is observed.course. After mixing of ethereal solutions of the starting materials at -78"C, slow warming up to room temperature and stirring for 16 h the bicyclic compounds 3 are obtained in 79 and 67% yield, respectively. The synthesis of 3b is accompanied by the formation of small amounts (approx. 3%) of a 2:4 adduct of l b and 2. However, we have not yet been able to assign a satisfactory structure to this material; indications for aniline-type structures (compare ref.[*]) wer...

Photochemical Synthesis of Prochiral Dialkyl 3,3-Dialkylcyclopropene-1,2-dicarboxylates with Facial Shielding Substituents and Related Substrates

“…[10] For 1αa (Figure 24), the entire molecule lies on a crystallographic mirror plane, with the exception of the methyl groups C (8) and C(8Ј). [27] Figure 25. The dimensions of the cyclopropene group are in good agreement with results found for other cyclopropene structures, with a double bond length of about 1.30 Å and single bond lengths of 1.52 Å .…”

Exploring the Reactivity of N-Alkynylated Sulfoximines: [2 + 2]-Cycloadditions

“…The formation of the allene derivative 6 was supposedly due to steric interactions which forced the cycloaddition to occur from the opposite end of the ketene resulting in a highly strained four-membered cyclic ether which subsequently rearranged to afford sulfoximine 6 (Scheme ), the structure of which was subsequently confirmed by X-ray analysis . The formation of amido-allenes during the [2 + 2]-cycloaddition process has been previously described by several other groups . Steric factors appear to have a larger influence on this reaction process than electronic ones…”

Hydroalumination of Ketenimines and Subsequent Reactions with Heterocumulenes: Synthesis of Unsaturated Amide Derivatives and 1,3-Diimines

“…Thus, the C -diaromatic ketenimine derivates 1a – c were generated following a literature procedure by elimination of water from the corresponding secondary amides 3 using P 4 O 10 in excess of anhydrous pyridine or triethylamine (Scheme , Route A). The C -dialiphatic ketenimines 1d – f were readily obtained by chlorination of the corresponding secondary amides 3 with phosphoryl chloride via established procedures to give imidoyl chlorides 4 , followed by their dehydrochlorination using an excess of triethylamine , (Scheme , Route B). These ketenimines reveal relatively low thermal stability and must be stored under argon at low temperatures (−20 °C).…”

“…8 Hz,0.4H,NCH(CH 3 (CH, phenyl), 127.2 (0.6C, CCH), 126.6, 126.5, 126.2, and 125.9 (CH, phenyl), 55.9 (N-CH, cyclohexyl), 53.0 (0.4C, NCH(CH 3 ) 2 ), 52.7 (NH-CH, cyclohexyl), 51.7 (0.6C, NCH(CH 3 ) 2 ), 58.1 and 50.1 (partially covered, N−CH−CH 2 ), 35.0 (N−CH-CH 2 ), 34.9, 32.9, 26.7, and 25.9 (N−CH-CH 2 −CH 2 ), 25.7 and 25.2, (N−CH-CH 2 − CH 2 −CH 2 ), 21.7 (NCHMe 2 ), 21.3 (NCHMe 2 ), *(Resonances of the main isomer are assigned (ration 6:4)). IR (ATR, cm −1 ) = 3412 w, 21;H,9.31;N,9.47. Found: C,80.84;H,9.41;N,9.34. Reactions of Active Al/N Compounds 5 with Isocyanates 9 and Isothiocyanates 14.…”