Furans from propargyl ketones

AryT3,4-fused furans 63 are synthesized in moderate to good yields from propargyl nucleophiles and a-sulfonyl a,p-unsaturated ketones under palladium catalysis conditions... 

Furans are formed from a-propargyl ketones. Alkynyl benzyl sulfides cyclize to give 2-aryl-2,3-dihydrothiophenes. Deprotonation at the benzylic position initiates the cyclization. 

In 2006, the group of Artok showed that 5-aryl-2(5H)-furanones could be prepared in moderate to good yields by a rhodium-catalyzed carbonylative arylation of internal alkynes with aryl boronic acids (Scheme 1.9a) [22]. a,P-Unsaturated ketones (chal-cone derivatives) were formed as the major product when some TFA (trifluoroacetic acid) was added under the same reaction conditions [23a]. By varying the catalytic system, indanones could be produced as the main product [23b]. The chemical behavior of terminal alkynes is different, and either a,P-unsaturated ketones or furans starting from propargylic alcohols can be achieved (Scheme 1.9b) [24, 25]. In the case of vinyl ketones, 1,4-diketones were obtained by rhodium-catalyzed coupling of arylboronic acids in the presence of 20-40 bar of CO [26]. In 2007, Chatani demonstrated that indenones could be accessed by a carbonylative rhodium-catalyzed cyclization of alkynes with 2-bromophenylboronic adds (Scheme 1.9c) [27]. Here, the key intermediate is a vinylrhodium(I) spedes that is formed by transmetaUation of RhCl with 2-bromophenylboronic acid followed by insertion of... 

Isomerization of an a-allenylcyclopentenone, obtained from a propargyl ether and a mopholino a,p-unsaturated amide, in the presence of Hg-catalyst to a furanyl cyclopentenone provided another example of the conversion of allenyl ketones to furans <03OLl 171>. 

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