Construction of CF₃-Containing Tetrahydropyrano[3,2-b]indoles through DMAP-Catalyzed [4+1]/[3+3] Domino Sequential Annulation

Abstract

A [4+1]/[3+3] domino sequential annulation reaction of o-aminotrifluoroacetophenone derivatives and β′-acetoxy allenoates enabled by DMAP has been reported. A variety of CF3-containing tetrahydropyrano­[3,2-b]­indoles were obtained as a single diastereomer in high yields (≤98%) under mild conditions. The reaction can build one C–N bond, one C–C bond, and one C–O bond sequentially in a single step. The synthetic utility was demonstrated with gram-scale reactions and various transformations of the products.

Calcium-catalyzed dehydrative allylation of P-ylides and sequential Wittig reaction for streamlined access to versatile 1,4-dienes

“…In the presence of NEt 3 , the P-ylides can be stabilized, probably owing to the basic environment. 16 As expected, a lower yield of 3a was obtained when NEt 3 was absent (Table 1, entry 2). Further investigation revealed that the calcium catalyst was crucial for this transformation.…”

Switchable Selectivity in the Annulation of o‐Trifluoroacetylanilines and Activated Terminal Alkynes Based on Transition Metal and Phosphine Catalysis

“…Phosphine catalysis is a powerful tool for organic synthesis [11] . It is widely used in the catalysis of reactions of acceptor alkynes and allenes with o ‐trifluoroacetylanilines to obtain complex trifluoromethyl substituted heterocycles [8i–l] . However the reaction of o ‐trifluoroacetylanilines with propiolates under the conditions of phosphine catalysis has not been suggested so far.…”

Pyridine vs DABCO vs TBAB in Annulations of δ-Acetoxy Allenoates with Thioamides Leading to Dihydrothiophene, Thiopyran, and Thiazole Scaffolds

“…The significant reactivity differences between the Lewis bases DABCO (p K a H 8.8) and pyridine (p K a H 5.2) or DMAP (p K a H 9.2) have been alluded to in several reports earlier. , Acetoxy allenoate I can undergo S N 2′-attack with an amine to give ammonium ion intermediate II . In the case of pyridine, the positive charge on the nitrogen atom is stabilized by the aromatic ring in the formation of ylide IV , an analogue of phosphonium ylide.…”

“…Introduction of an acetoxy functionality at the β′/δ-position of allenoate can produce diene-phosphonium or ammonium intermediate and is elegantly exploited by several groups. , In general, amines are less nucleophilic than substituted phosphines . Therefore, the corresponding amine analogues of phosphine-catalyzed reactions involving allenoates have received less attention and successful examples are relatively rare. , …”