Halogen‐Exchange Fluorination of β‐Chlorovinyl Aldehydes – Unexpected Cascade Transformations in the Fluorination of 4‐Chloro‐2H‐chromene and 4‐Chloro‐2H‐thiochromene‐3‐carbaldehydes. Issue 36 (13th September 2019)

• Record Type: Journal Article
• Authors: Somasundaram, Muthuramalingam; Garg, Jai Anand; Naidu, Shivaji; Ramkumar, Venkatachalam; Saiganesh, Ramanathan; Kabilan, Senthamaraikannan; Balasubramanian, Kalpattu Kuppuswamy
• Is Part Of: European journal of organic chemistry. Issue 36(2019)
• Page Start: 6269
• Page End: 6277
• Publication Date: 2019-09-13
• Subjects: Halex -- Fluorination -- Aldehydes -- Bis‐Hemiacetalization -- Reaction mechanisms; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.201901069
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract : Halogen‐exchange (Halex) fluorinations in vinylic systems are rare; under controlled conditions, halex fluorination of vinylic aldehydes, 1‐chloro‐3 H ‐benzo[ f ]chromene‐2‐carbaldehyde (8 ) and 4‐chloro‐2 H ‐benzo[ h ]chromene‐3‐carbaldehyde (11 ) successfully furnished their respective fluoro exchanged derivatives 1‐fluoro‐3 H ‐benzo[ f ]chromene‐2‐carbaldehyde 9 and 4‐fluoro‐2 H ‐benzo[ h ]chromene‐3‐carbaldehyde 12 . However, 4‐chlorobenzopyran‐3‐carbadehydes (3 ) underwent a novel cascade reaction exclusively via the fluorine exchanged intermediate to afford 2, 3‐dihydro‐3, 3′‐methylenebischromones (4 ). Under similar conditions, in a somewhat different manner, the thio analogous system, 4‐chlorobenzothiopyran‐3‐carbaldehydes (1 ) yielded 3, 3′‐methylene bisthiochromen‐4‐ones (2 ) also in a domino fashion. Sterically hindered vinylic aldehyde, 4‐chloro‐2, 2‐dimethyl‐benzopyran‐3‐carbaldehyde (18 ) exhibited a totally different behavior by affording a bicyclic benzopyran annulated bisacetal (19 ). The mechanism of these transformations has been investigated. Abstract : One of the most facile and robust ways of incorporating fluorine atoms in organic substrates is through the Halex fluorination. We have described here the Halex fluorination of β‐chlorovinyl aldehydes using KF/DMSO system under mild conditions. Further the transformation of the fluoro‐substituted intermediates to its dimeric compounds via a cascade sequence of six steps is discussed.