ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In CHCl3, CH3CN, or AcOH, benzeneselenenyl chloride (PhSeCl), bromide (PhSeBr), and acetate (PhSeOAc), 2-nitrobenzenesulfenyl chloride (NO2C6H4SCl), and 2,4-dinitrobenzenesulfenyl chloride ((NO2)2C6H3SCl) added to bicyclo[2.2.1]hept-5-en-2-one (5) in an. anti fashion with complete stereo- and regioselectivity, giving adducts 20-24 in which the chloride, bromide, or acetoxy substituent (X) occupies the endo position at C(6) and the Se- or S-substituent (E) the exo position at C(5), The addition 5+ (NO2)2C6H3SCl→24 was accompanied by the formation of (1RS, 2RS)-2-(2,4-dinitrophenylthio)cyclopent-3-ene-l-acetic acid (25). The latter was the major product in AcOH containing LiClO4. The additions of PhSeCl and PhSeBr to bicyclo[2.2.2]oct-5-en-2-one (6) were less stereoselective (proportion of exo vs. endo mode of electrophilic attack was ca. 3:1) but highly regioselective gazing adducts 27/28 and 29/30, respectively, the regioselectivity being the same as that of the electrophilic additions of 5. The reaction of PhSeCl with a 4:1 mixture of 2-exo-chloro- and 2-endo-chlorobicyclo[2.2.1]hept-5-ene-2-carbonitriles (12) was slower than addition 5+ PhSeCl; it gave adducts 31/32 (4:1) in which the PhSe moiety occupies the exo position at C(6) and the Cl atom the endo position at C(5). The addition of PhSeCl to 2-chlorobicyclo[2.2.1]oct-5-ene-2-carbonitriles (13) was very slow and gave adducts with the same regioselectivity as 12 + PhSeCl, but opposite with that of reactions of the corresponding enones 5 and 6. PhSeX (X = Cl, Br, OAc) added to 2-cyanobicyclo[2.2.1]hept-5-en-2-yl acetates (14) with the same regioselectivity as 12 + PhSeCl. The additions of PhSeCl, PhSeBr, NO2C6H4SCl, and (NO2)2C6H3SCl to 2-(bicyclo[2.2.1]hept-5-en-2-ylidene)propanedinitrile (49) were not regioselective, showing that a dicyanomethylidene function is not like a carbonyl function when homoconjugated with a π system. The results are in agreement with predictions based on MO calculations suggesting that a carbonyl group homoconjugated with an electron-deficient centre can behave as an electron-donating, remote substituent because of favourable n(CO)↔σC(1), C(2)↔p(C(6) hyperconjugative interaction.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19890720519
