ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The title compounds 1a and 1b have been synthesized in two steps from the saturated pyran-3-ones 2a and 2b, respectively. Upon irradiation (254 nm or 350 nm) in dilute solutions (10-3-10-2M), compounds 1 undergo a formal [4 + 2] cycloreversion from the excited triplet state to give (2-methylprop-1-enyl)ketene (11) and either formaldehyde or acetone, ketene 11 being trapped by H2O or MeOH to afford 4-methylpent-3-enoic acid (5) or its methyl ester 4 in 75-85% isolated yield. In this (monomolecular) photoreaction, heterocycles 1 differ from their alicyclic counterparts, i.e., 4,4-dimethylcyclohex-2-enone (10a) and 4,4,6,6-tetramethylcyclohex-2-enone (10b), as no rearrangement to a 4-oxabicyclo[3.1.0]hexan-2-one occurs. On the other hand, the photochemical behavior of pyranone 1a in bimolecular reactions (cyclodimerization, [2 + 2] cycloaddition to 2,3-dimethylbut-2-ene) resembles that of enone 10a.
Additional Material:
1 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19940770404
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