Four-Membered Rings from Isocyanides - Recent Advances

Four-membered rings from isocyanides: Developments since the mid 1980s

“…1 The period till 1985, however, proved prolific to such an extent as to warrant a second review. 2 Since that time again new results have emerged in great number; this may justify the present survey. 3 Viewing the rich material, two features stand out: (i) The ring-forming principles have almost trebled so as to exclude an introductory graphic of the kind shown in ref.…”

“…giving cyclobutenediimines. 2 However, a four-membered ring may arise from that reagent by another route. Indeed, a more recent study using cyclohexyl isocyanide has shown that -besides the cyclopenta[b]pyridine 109 (including minor quantities of an isomer and a 1-azaspiro[4.4]nonatriene) -the cyclohepta-anellated azetidinimine 110 was formed (Scheme 25).…”

“…3 Viewing the rich material, two features stand out: (i) The ring-forming principles have almost trebled so as to exclude an introductory graphic of the kind shown in ref. 2 ; (ii) regarding the type of products, a plethora of element-organic rings have arisen. 4 Adhering to style and format of the earlier review, 2 presentation of all new material will be arranged according to starting compounds rather than to products or actual mechanisms.…”

New Syntheses and Ring Expansion Reactions of Cyclobutenimines

“…Cyclobutenimmonium structures were also obtained by [2þ2] cycloaddition of ynamines and the related a-chloroenamines to give chlorides 10 [25,26] or by alkylation of squaric acid amides to give products 11 (Scheme 2). [9,27] In another approach, cyclopropenones [28][29][30][31] or their all-carbon analogues, triafulvenes, react with isonitriles to give cyclobutenimines of type 12 and 13, respectively (Scheme 2). [32] Recently, the conversion of 2,2,4,4-tetrachlorocyclobutanimines 14 to cyclobutenimine acetals 15 by the action of alkoxide in a mixed elimination/substitution process was reported (Scheme 3).…”

Addition of isocyanides to ?-(methylthio)-benzylidenamidinium iodides: A surprising access to 2-(dialkylamino)imidazoles and 3,5-diamino-2H-pyrrolium salts

“…On the other hand, isocyanides are a class of compounds of great use due to their unique nucleophilic character [3,4]. Their interest has been widely demonstrated in heterocyclic synthesis [5,6]. We previously reported the protonation of 1,3-diazabutadi- enes to yield imidazole or triazine derivatives by addition of isocyanides.…”