Benzo-e-lactones

The Ye group have established an unprecedented NHC-catalyzed [3 + 4] annulation of enals with o-quinone methides to give the corresponding benzo-e-lactones. The reaction worked well for both p-aryl enals and p-alkyl enals, giving the corresponding benzo-e-lactones in high yields with moderate (for p-aryl enals, 3 1-5 1 dr, 81-95% ee) to excellent (for p-alkyl... 

The NHC (307) has been employed as a catalyst for the [4 + 3] annulation of enals (311) (R = alkyl, aryl) with o-quinone methides (312) (R = aryl, cinnamyl), which afforded benzo-e-lactones (313) with 81-98% ee and 3 1-20 1 dr. The free hydroxy (g) group in the catalyst turned out to be the key feature and is believed to steer the substrate by hydrogen bonding. ... 

Scheme 4.18 Synthesis of benzo-e-lactones by A -heterocyclic carbine-catalyzed [4-1-3]...

Lv, H., Jia, W.-Q., Sun, L.-H., Ye, S. (2013). N-heterocyclic carbene catalyzed [4-1-3] Annulation of enals and o-quinone methides highly enantioselective synthesis of benzo-e-lactones. Angewandte Chemie International Edition, 52, 8607-8610. 

Particularly important is the influence of the metal countercation e.g., cleavage of the achiral lactone l,3-dimethyl-6//-benzo[ ,]naphtho[1.2-d]pyran-6-one in toluene at — 40 CC, using different metal alkoxides, e.g., (+)-menthol as inexpensive chiral 0-nucleophiles, gives atropisomer ratios of 81 19 for lithium, 66 34 for sodium, and 63 37 for potassium. In other solvents (e.g., THF), this selectivity order may be reversed14. 

Benzo[6]furan and 2-methylbenzo[6]furan fail to undergo photooxygenation but 2,3-dimethyIbenzo[6]furan yields 2-acetoxyacetophenone (364). At -78 °C the peroxide (363) is produced which at higher temperature rearranges to the acetophenone (364 Scheme 98). 2-Vinylbenzo[6 Jfurans, e.g. trans- 2- styrylbenzo[6 Jfuran (365 Scheme 99), yield photooxides which may be isolated. Compound (366) on treatment with a catalytic amount of triethylamine yields the lactone (367) (77BCJ3026). 

Beilstein Handbook Reference) AI3-00753 Benzo-a-pyrone BRN 0383644 Caswell No. 259C CCRIS 181 Cinnamic acid, o-hydroxy-, 8-lKtone ois-o-Coumaric acid anhydride Coumarin cis-o-Coumarinic acid lactone Coumarinic anhydride Coumarinic lactone Cumarin EINECS 202-086-7 EPA Pesticide Chemical Code 127301 HSDB 1623 o-Hydroxycinnamic lactone 0-Hydroxyzimtsaure-lacton Kumarin NCI C07103 NSC 8774 Rattex Tonka bean camphor. Used in pharmaceuticals as a flavorant. Crystals mpo 71" bp = 301.7 d O = 0.936 Xm = 273, 311 nm (e = 11200, 6710, MeOH) moderately soluble in H2O, EtOH, more soluble in EtzO, CHCI3, C5H5N. Alfa Aesar Rhodia Inc. Rhodia Organique Fine Ltd. 

A mixture of 3-carbethoxy-3-(2 -phenylcyclohept-l-en-l-yl)propionic acid and polyphosphoric acid heated 3 hrs. at 100° with stirring -> 6,7-benzo-4,5-cyclo-heptenocoumaran-2-one. Y 82%.—This is a new type of ring closure characterized by the formation of a naphthalene ring condensed to a y-lactone ring. It appears to be general for acid-esters, acid-lactones, and dicarboxylic acids derived from the Stobbe products of benzyl ketones. F. e. s. S. Yaroslavsky and E. D. Bergmann, Tetrahedron 11, 158 (1960). 

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