ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The cycloadditions of methyl propynoate and methyl vinyl ketone to 5,6-dimethylidene-2-norbornanone (6) are para′-regioselective“Para” (p) designs in this paper the 4, 9-disubstituted tricclo[6.2.1.02, 7] undecane- and 4, 9-disubsstituted tricycle[6.2.202,7] dodecane derivatives, “meta” (m) design the corresponding 4, 10-disubstituted compounds.. A smaller para -regioselectivity is observed for the addition of methyl propynoate to 5,6-dimethylidene-2bicyclo[2.2.2]octanone (10). No regioselectivity is observed with 5,6-dimethylidene-2exo-norbornyl alcohol (3), acetate (5) and 5,6-dimethylidene-2exo-bicyclo[2.2.2]octanol (9). PMO arguments based on the shape of the HOMO's and subHOMO's of the dienes allow to rationalize these observations. Unpredictable para′- or ‘meta’regioselectivities are found for the Diels,-Alder additions of 5,6-dimethylidene-2endo-norbornyl alcohol (2), acetate (4) and 5,6-dimethylidene-2endo-bicyclo[2.2.2]octanol (8). The carbonyl group of β,γ unsaturated ketones such as 6 and 10 can act as an electron donating homoconjugated substituent. The n(CO) ↔ σ[C(1), C(2)] ↔ π[C(5), C(6)] hyperconjugative interaction can override the usual electron-withdrawing effect of this function.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19820650118