Amidines dehydrohalogenation

DEHYDROHALOGENATION Amidines, bicyclic. N-Bromosuccinimide. I, S-Dia-zabicyclo[4.3.0 nonene-5. Diethylamine. Dimethyl sulfoxide. Hexamethylphosphor-ic triamide. Lithium bromide. Potassium r-butoxkle. Sodium amidc-Sodium r-but-oxide. Tetia-n-butylammonium bromide. Triethylamine. 

Dehydrohalogenation of amide chlorides affords a-chloroenamines, which undergo cycloaddition with IV-diphenylmethylaldimines to furnish azetidinium salts (303 equation 161). From these salts the diphe-nylmethyl group can be removed by hydrogenation, subsequent deprotonation yields 2-amino-1-aze-tines. The addition of primary or secondary amines to nitrilium salts gives rise to formation of amidinium salts and amidines respectively, e.g. (304 equation 162). In a similar reaction from copper(I) imidazolide, r-butyl bromide and nitriles amidines (305 equation 163) were prepared. ... 

Dehydrohalogenation. This base is a superior reagent for effecting dehydro-halogenation. Truscheit and Eiter were unable to dehydrochlorinate the chloro ester (1) with usual tertiary bases (pyridine, quinoline, N,N-dimethylaniline) but by stirring a mixture with the bicyclic amidine base at 90°, adding ice and sulfuric acid, and working up the neutral fraction, they obtained in 85% yield a 70 30 mixture of cis- and trans-methyl tridecene-lO-yne-12-oate (3). 

On the other hand, in the 1960s sterically hindered bicyclic amidines, 1,8-diazabicylo [5.4.0]undec-7-ene (DBU) (1) and l,5-diazabicylo[4.3.0]non-5-ene (DBN) (2), were introduced as useful dehydrohalogenation reagents in the synthesis of vitamin A. Treatment... 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

Two Nitrogen Attnns (1 ).—The use of bicyclic amidines (168), particularly as dehydrohalogenating agents, has been reviewed. ... 

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