By F. Voegtle
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Extra resources for Cyclophanes I
By variation of several dilution principle conditions, the result regarding the yield of 119f starting with 120 could not be improved. g. a mixture of THF/DMF (9:1), tile yield decreased even more from 18 % to 9 %. Also, the use of LiH as a base in DMF decreases the amount of 119fto 8 %. Compared to the yields of 119d, h, the amounts of 121d (17%) and 121h (11%) also are quite low 156) Macrocycle 125 with a ring width of 27 C-atoms, containing three diethyl malonate units, was recently prepared lss) No details of the cyclization are mentioned by the authors, apart from the note that the cyclization was carried out under dilution principle conditions.
There is a connection between the reaction temperature and the cyclization time: the lower the temperature, the longer - - understandably -- the reaction time must be chosen. This time varies from 6 days to 6 hrs. d) The addition of pyridine as a HCl-binding agent is not absolutely necessary. The pyridine seems to accelerate the cyclization reaction; otherwise longer reaction times were needed, e) The yields vary strongly and depend on many different factors, discussed in the original literature 2o2-212) The synthesis of thiolesters zo4,2o8,21o,211) in principle doesn't differ from the type of preparation of the oxaesters.
Also, the necessity to employ strong bases in excess, limits this classical direct C--C-coupling method to educts and products that are insensitive to bases. 3]carbaphanes is favourably achieved by the thiaphane method. 3]carbaphane esters succeeded only in using monoalkylated dialkyl malonates as the starting material. 2]metacyclophane (128) and its dimer 129. Diethyl malonate (120) was cyctized with 3,3'-bis(bromomethyl)bibenzyl (127) in boiling xylene with excess Nail 16o) + C02E t CIH2 C02Et 127 120 NaHI xytene 128 129 39 Ludovica Rossa and Fritz V6gtle In this 1C-DP-reaction 6a) the 11-membered diester 128 was obtained in 11 ~o yield, the dimer 129 was formed in higher yield of 16% 16o).
Cyclophanes I by F. Voegtle