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6‐Siloxy‐Substituted 5,6‐Dihydro‐4 H ‐1,2‐oxazines as Key Building Blocks for Natural Products
Author(s) -
Zimmer Reinhold,
Collas Markus,
Roth Michael,
Reißig HansUlrich
Publication year - 1992
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.1992199201119
Subject(s) - chemistry , oxazines , key (lock) , natural (archaeology) , combinatorial chemistry , organic chemistry , computer science , computer security , archaeology , history
Methyl ( E )‐5‐bromo‐4‐oxo‐2‐pentenoate ( 6 ) and the corresponding oxime 5 were prepared in high yields by starting from methyl levulinate ( 3 ). The novel nitrosoalkene 8 , generated in situ from oxime 5 , smoothly added to silyl enol ether 7 to give 1,2‐oxazine 9 and nitrone 10 as byproduct. Methods are described transforming intermediate 9 into unsaturated diketo ester 11 , or oximes 13 , 15 , and 18 , which may serve as precursors of pyrenophorin. Reductive ring cleavage of 1,2‐oxazine 9 with Raney nickel efficiently afforded the saturated diketo ester 19 . Its intramolecular aldol reaction gave cyclopentenone derivative 20 , which is a known precursor of ( Z )‐jasmone. Cycloaddition of methyl α‐nitrosoacrylate to silyl enol ether 22 provided 1,2‐oxazine 23 . This compound was directly converted into the ant‐trail pheromone 24 by hexacarbonylmolybdenum‐promoted ring contraction.