Cyclization, aryne-mediated

Substituted benzoMisothiazole d, d -dioxides 498 were synthesized through lithiation of 497 (X = H, F, Cl), aryne-mediated cyclization giving intermediates like 53a and subsequent quenching of aryllithium intermediates with various electrophiles (see Section 4.05.4.5) <1997T3615>. 

Scheme 19. Glycozolidine synthesis via consecutive Stille and aryne-mediated cyclization...

Similarly, an aryne-mediated cyclization process has been efficiently employed by Couture et al. as a key step in the total synthesis of the alkaloids eupolauramine (Scheme 12.8) [20] and nuevamine (Equation 12.15) [21]. 

Oxazoles were used in the Kondrat eva reaction for the synthesis of pyridine-based compounds (13OL2530, 13OL3550). A continuous flow procedure was reported for a scalable synthesis of benzoxazoles 137 starting form 3-halo-N-acyl anilines 136 (130L5546). The reaction proceeded via a base-mediated elimination of the 3-halo substituents to give an aryne intermediate that underwent intramolecular cyclization to provide lithiated benzoxazoles that were quenched in-line by addition of electrophiles (E ). 

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