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Synthesis of Sulfur‐Containing Tricyclic Ring Systems by Means of Photoinduced Decarboxylative Cyclizations
Author(s) -
Griesbeck Axel G.,
Oelgemöller Michael,
Lex Johann,
Haeuseler Andreas,
Schmittel Michael
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200105)2001:10<1831::aid-ejoc1831>3.0.co;2-7
Subject(s) - chemistry , intramolecular force , decarboxylation , intermolecular force , carboxylate , ring (chemistry) , photoinduced electron transfer , medicinal chemistry , sulfur , photochemistry , tricyclic , stereochemistry , electron transfer , organic chemistry , molecule , catalysis
The intramolecular and intermolecular photoinduced electron transfer reactions of a series of mercaptoacetic acid and mercaptopropionic acid derivatives were investigated. In the intermolecular series, the phthalimidoalkylsulfanylalkylcarboxylates 1a − j and 2 were transformed into the tricyclic ring systems 3a − j and 4 , respectively, with high regioselectivities. The mercaptoacetic acid and 2‐mercaptopropionic acid derived substrates 1a − g and 2 readily cyclized in good to excellent yields (60−98%) but with low diastereoselectivities (except for 1d ), whereas the corresponding 3‐mercaptopropionic acid derived substrates 1h − j gave the corresponding tricyclic products 3h − j after prolonged irradiation, but with poor yields (11−20%). The intermolecular version − i.e., photodecarboxylative addition to N ‐methylphthalimide ( 5 ) as electron acceptor − was successful with mercaptoacetic acid, and 2‐mercaptopropionic acid substrates 6a − c and the addition products 7a − c were obtained in high yields (57−90%). No addition, however, was observed with 3‐(methylsulfanyl)propionic acid ( 6d ). The regioselectivity of decarboxylation proceeded in a controlled manner for the mercaptosuccinic acid derivatives in both the intramolecular (with 8a − c ) and the intermolecular (with 9 ) versions. Comparison between sulfur‐activated and nonactivated species ( 13 , 15 ) or irradiation of 1a under nonactivating conditions showed that the carboxylate anion in the position α to the electron‐donating sulfur atom acts as a superior leaving group. This efficiency is drastically reduced for carboxylate anions in the β position. With the former substrates, the photochemical cyclization proceeds with high product yields. Quantum yield measurements for decomposition (Φ d as a measure for cyclization) supported these observations. CV measurements indicated preorientation prior to electron transfer in the intramolecular pathway.