Molecular Transformation to Pyrroles, Pentafulvenes, and Pyrrolopyridines by [2+2] Cycloaddition of Propargylamines with Tetracyanoethylene

Abstract

In this paper,w ed escribe an efficient and atomeconomicals ynthesis of highly functionalized pyrroles, pentafulvenes, and pyrrolopyridinesb y[ 2 + +2] cycloaddition-retroelectrocyclization of N-substituted propargylamines with tetracyanoethylene,f ollowed by the treatment of the resultingt etracyanobutadiened erivatives with silica gel. In this reaction, silica gel plays an important role to promote the intramolecular cyclization to afford the heterocyclic products from the tetracyanobutadiene intermediates. The products were obtaineds electively depending on the substituent on the nitrogen atom of the starting propargylamines.Scheme1.Our previous study and planneds trategy to access highly functionalized pyrrole derivatives.[a] Prof.

Recent Advances in the Functionalization of Azulene Through Pd‐Catalyzed Cross‐Coupling Reactions

“…Likewise, 1,3‐diethynylazulenes 314 a and 314 b could be obtained in 90 and 42 % yields, respectively, from the corresponding diiodoazulenes by cross‐coupling with two equivalents of TMSA followed by deprotection upon treatment with methanolic potassium hydroxide (Fig. 8) [57,132,133] . In a similar manner, 1,2‐di‐ and 1,2,3‐triethynylazulenes 315 and 316 were obtained as greenish‐blue crystals in 98 % and 96 % yields, respectively, by the reaction of 309 b with one or two equivalents of N ‐iodosuccinimide followed by coupling with TMSA under Sonogashira conditions and subsequent desilylation (Figure 15).…”

“…This method could be used to make functionalized 1‐ethynylazulenes 303 – 308 via Pd‐catalyzed cross‐coupling of the corresponding iodoazulenes with trimethylsilylacetylene and subsequent desilylation (Figure 13). [57,125–133] …”

Alkynylazulenes as Building Blocks for Highly Unsaturated Scaffolds

“…reported also the synthesis of some functionalized ethynylazulenes namely, N ‐(3‐(azulen‐1‐yl)prop‐2‐yn‐1‐yl)‐4‐methylbenzenesulfonamides 22 a – h , tert ‐butyl (3‐(azulen‐1‐yl)prop‐2‐yn‐1‐yl)carbamate 23 a – j and 3‐(azulen‐1‐yl)prop‐2‐yn‐1‐ol 24 a – j by coupling of the appropriate 1‐iodoazulenes with each of N ‐tosyl propargylamine, N ‐ tert ‐butoxycarbonylpropargylamine and 2‐propyn‐1‐ol, respectively (Figures 4–6). [29,30] …”

“…In this reaction, silica gel plays an important role to promote the intramolecular cyclization to afford the heterocyclic products from the tetracyanobutadiene intermediates (Scheme 87). [30] …”

“…The corresponding pentafulvenes were obtained in high yields with azulenes possessing an electron‐withdrawing group, but the reaction of azulenes having an electron‐donating group resulted in lower product yields due to the decomposition of the products during the treatment with silica gel (Scheme 88). [30] …”