Subject: SUM: radical cyclizations

From: [email-masked]
Date: Tue, 19 Jul 1994 22:01:34 +0200 (MES)

Hallo,

A few weeks ago I posted a question concering radical cyclization and
asked what there is anything known of its calculation.
I have been asked to sum it for the others which is what I am doing with pleasure
now.

I would like to take the chance to say a big 'thank you' to all the contributers.
It was a great help for me.

The original question was:

> For the explanation of experimental data I am interested
> in finding the transition states of radical addition or
> cyclisation reactions like for example a 6-exo-trig reaction.

> Is there anyone aware of recent ab-initio or better semi-empirical
> calculations which revealed the TS of any type of a radical addition
> or cyclisation?

These are the answers:

------------------------

You might want to look at this paper describing a force-field approach
to modeling the transitions states of intramolecular cyclization reactions.   
(Spellmeyer and Houk, J. Org. Chem., 1987, 52(6), 959-974.)  
The force-field was optimized to produce minima that looked like the
transition states of intermolecular radical additions calculated with
ab initio methods.  The force-field was further optimized to give accurate
delta-Es for the regio-selectivity and stereo-selectivity observed in 
several intramolecular radical cyclization reactions.  

The accuracy of the model was tested by comparing TSs calculated using ab 
initio methods (UHF/STO-3G was the highest level we could run at the time) 
against the "transition states" we calculated using our force-field.  They were 
nearly indistinguishable.  These results differed from TSs calculated
with MINDO/3, and MNDO.

Beckwith and Schiesser have published a different force-field based on
intermolecular TSs found using MNDO (Tetrahedron Letts, 1985, 26, 373).

I hope this gives you a good place to start.  I'd be happy to provide
more information if you want.

Good luck,

David Spellmeyer
Chiron Coporation
4560 Horton Street
Emeryville, CA 94608
(510)-601-3313 Voice
(510)-601-3360 FAX
[email-masked] e-mail

----------------------------------

Dear Dr.Loehl,

   I hope the following references on localization of TSs for addition
reactions of radicals can be of some help. We are currently studying 
structure and reactivity of radical cations, but the kind of TSs on which
we have long experience are those corresponding to internal migrations and
abstraction processes. Anyway, if you have any specific question on metho-
dological aspects, we will be pleased of trying to help you.

[1] Features of the Potential Energy Surface for Reactions of OH with CH2O
    M.R.Soto and M.Page
    J.Phys.Chem., 1990, 94, 3242

[2] Computational Study of Addition and Abstraction Reactions between OH
    Radical and Dymethyl Sulfide. A Difficult Case.
    M.L.McKee
    J.Phys.Chem, 1993, 97, 10971

[3] Computational study of the Addition of OH radical to S=C=S
    M.L.McKee
    Chem.Phys.Lett., 1993, 201, 41
  
[4] Radical Addition to HNO. 
    M.Page and M.R.Soto
    J.Chem.Phys., 1993, 99, 7709

[5] Addition of O(3P) to CF3O
    Z.Li and J.S.Francisco
    Chem.Phys.Lett., 1993, 209, 151
    
Yours,
            Laura

<<<<<<<<<<<<<<<<<<<<<<<<<<OOOOOOOOOOOOOOOOO>>>>>>>>>>>>>>>>>>>>>>
!                                                               !
!  Laura Coitino                                                !
!  Universita di Pisa - Dip.to di Chimica e Chim Industriale    !
!  Via Risorgimento, 35. I-56100 Pisa, Italy                    !
!  Phone:  Voice (+39-50)-918204                                !
!          Fax   (+39-50)-502270                                !
!  E-mail: [email-masked]                        !
!        : [email-masked]                        !
!                                                               !
<<<<<<<<<<<<<<<<<<<<<<<<<<OOOOOOOOOOOOOOOOO>>>>>>>>>>>>>>>>>>>>>>

------------------------------------------

I've been doing computations of TS's for the addition of HO an (3P)O to va-
rious compounds, mostly by semiempirical methods.  Unfortunately I don't have
a ref. list handy:  what's been published has been in conjunction with exper-
iments  (silent discharge plasma decomposition).  I find that Cl-containing
compounds are quite difficult.  For CHO compounds, the computations are rather
straightforward:  start from your product, do a reaction coordinate to sepa-
rate it into reagents, pick the highest energy point to optimize to a transi-
tion state..... (using keywords like TS in MOPAC--not NEARLY as successful as
their writeup would have you believe--SIGMA in AMPAC--another tricky one--
LTRD, POWELL, NLLSQ-also in MOPAC).  Do you have access to Chem Abstracts on-
line?  If so, it shouldn't be hard to do a literature search....  Let me know
if you have some more specific questions.  I have a lot of computer time avail-
able, so could do a bit of trouble-shooting of your inputs.  (Right now I have
more computer time than my own time, but people have helped me in the past...)
Irene Newhouse

-----------------------------------------------

It's not a radical reaction, but I published ab initio work on a 6-endo-trig
reaction in which focussed on the distortion of the TS due to the cycle.  Here
is the reference:

C.I.Bayly and F.Grein, "Comparison of an intramolecular Michael-type addition
to its intermolecular counterpart: an ab initio theoretical study", Canadian
Journal of Chemistry, vol. 67, pp. 2137-2177 (1989).

Christopher Bayly

-------------------------------

Best wishes and thank you very much 

Thosrten

-- 

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|Thorsten Loehl                            Tel.:+49-251/83-3233      |
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