Journal of the Chemical Society. Perkin transactions I p. 2647 - 2654 (1982)
Update date:2022-08-29
Topics:
Bushby, Richard J.
Jesudason, Malini V.
Pollard, Michael D.
Shuhaibar, Khamis F.
Direct photolysis of 4-(<2H6>isopropylidene)-3,3,5,5-tetramethyl-1-pyrazoline (11) is believed to proceed via a singlet trimethylene-methane (TMM).It gives mainly the 'least motions' product (<2H6>isopropylidene)-2,2,3,3-tetramethylcyclopropane (12).This implies that the singlet TMM adopts a bis-orthogonal geometry (21) rather than the mono-orthogonal geometry (20) expected.Direct photolysis of 13 different α-methylated 4-alkylidenepyrazolines (5) shows, that in this series, formation of the 'least motions' product (22) is normally preferred.In the initially formed bis-orthogonal biradicals, the ability of C-CMe2 rotation to complete with ring closure seems to be determined by steric factors.Generally, the tendency to form the 'least motions' product (22) is greatest in those cases where the alkylidene group bears two substituents (X,Y <*> H), less where there is one (X = H, Y <*> H), and least of all where there is none at all (X,Y = H).The two main exceptions to this least motions rule are for 4-(2',2',3',3'-tetramethylcyclopropylidene)-3,3,5,5-tetramethyl-1-pyrazoline (27) and for 3,3,5,5-tetramethyl-1-pyrazolin-4-ylidenemalononitrile (32).In both of these cases there may be special factors which destabilise the 'least-motions' product.By way of contrast to the direct photolysis, triplet sensitised photolysis of 4-(<2H6>isopropylidene-3,3,5,5-tetramethyl-1-pyrazoline (11) gives a statistical mixture of the deuterated methylenecyclopropanes (12) and (13).This is consistent with the expected planar geometry (19 or the kinetic equivalent thereof) of the triplet TMM biradical.Some examples of the photochemical interconversion of methylenecyclopropanes and one example of a photochemical reduction of a pyrazoline are also reported.
View MoreChongqing Shuangfeng Chemical Co.,Ltd
Contact:+86-23-49850156
Address:No.663,xuanhua Rd,yongchuan,chongqing,China
Contact:410-273-7300; 800-221-3953
Address:4609 Richlynn Dr., PO Box 369, Belcamp, MD, 21017-0369, USA
Taizhou volsen chemical Co., Ltd
website:http://www.volsenchem.com
Contact:+86-576-88869393
Address:Jiaojiang District, Taizhou, Zhejiang, China.
Contact:+49-4101-3053-0
Address:Waldhofstrasse 14 ,25474 Ellerbek Germany
Contact:86-371-63655023
Address:No.85,jinshui road,zhengzhou,China
Doi:10.1039/c8cc09681c
(2019)Doi:10.1021/ja00864a040
(1962)Doi:10.1021/acs.joc.5b01604
(2015)Doi:10.1021/jo01140a013
(1952)Doi:10.1016/S0022-2860(01)00707-4
(2002)Doi:10.1080/00397919608003542
(1996)
