Labile tricyclic

Furthermore, the authors showed that compounds of type 1-78, easily accessible from 1-77, can be used as starting materials for the production of a new cyclo-propa[c]chromane framework 1-80 (Scheme 1.21). Oxidation of 1-77 to the corresponding sulfoxide and subsequent pyrolytic elimination generated the labile cyclobutene 1-78, which was directly epoxidized leading to the desired tricyclic compound 1-80 in 46% yield, probably via the epoxycyclobutane 1-79, again in a domino fashion. 

The double )5-scission pathway becomes dominant in bicyclic systems (Equations (7)-(9) and Scheme 13). Thus, cyclopentene ozonide (69) gives cyclopropane (Equation (7)) <68TL329l>. Photolysis of the ozonide derived from 1,4-benzodioxins (70) provides a method for the preparation of labile o-benzoquinones (71) (Scheme 13) <87JOC56l6>. Photolysis can also provide a route to unstable compounds and transient species such as the aziridine-2,3-dione (72) (Equation (8)), identified at 77 K using infrared spectroscopy <80JA6902>. Relatively unstable azacarbapenems (73) have been prepared by photolysis of tricyclic compounds containing a cyclobutene ozonide (Equation (9)). On silica, the 1,2,4-trithiolane (74) underwent photo-equilibration (Equation (10)) with the 1,3-dithetane (75) and sulfur. 

Lycorine is an alkaloid that has attracted attention from both the synthetic community and pharmacologists. Prior synthetic approaches have included inter-and intramolecular Diels-Alder cycloaddition. Based on a similar retrosynthetic disconnection, Padwa and co-workers (106,109) chose to use a push-pull carbonyl ylide cycloaddition with a disubstituted pyrrolidinone core to generate a tricyclic substrate. The major difference for this synthetic smdy was the availability of a labile proton a to the carbonyl moiety (Scheme 4.53). 

The interesting tricyclic compound 55 49), which has ( )-cycloheptene moiety, was found to be very labile and could only be trapped by condensing with diphenyl-isobenzofuran. 

Because of the enhanced rigidity of the higher-membered heteroannulenes, e.g. (36), imparted chiefly by the presence of properly positioned trans double bonds, these frames are generally less thermally labile than their heteronin counterparts although here too aromatic derivatives are substantially more heat resistant than their polyenic relatives. It was noted, for example (75PAC(44)69l), that while parent aza[13]annulene (37a) is thermally stable at 56 °C, its polyenic acetamide (36a) readily rearranges ( i/2< 1 h) under these conditions to what is believed to be a tricyclic isomer (96). 

Baldwin and Christie (18) have proposed that the origin of this difference almost certainly derives from a stereoelectronic factor. In 64 and 65, the Cg - S bond is more nearly orthogonal to the B-lactam amide plane than the C — S bons is, with respect to the thiazolidine amide plane (cf. 66). The Cg - S bond is therefore weaker than the CA - S bond and is preferentially cleaved. With tricyclic a-lactam 61, due to the five-membered ring, the C - S bond becomes more nearly orthogonal to the thiazolidine amide plane (cf. 67). As a consequence, the ordering of bond lability is reversed and the C — S bond is cleaved more readily. The stereoelectronically controlled step 61 63 has led to a stereospecific synthesis of a penicillin derivative from a peptide precursor. 

MAO inhibitors are indicated for depressed patients who are unresponsive or allergic to tricyclic antidepressants or who experience strong anxiety. Patients with low psychomotor activity may benefit from the stimulant properties of MAO inhibitors. These drugs are also useful in the treatment of phobic states. A special subcategory of depression, called atypical depression, may respond to MAOIs. Atypical depresssion is characterized by labile mood, rejection sensitivity and appetite disorders. 

The tricyclic compound 683 is a labile compound, which undergoes hydrolysis in water to regenerate 682. Repeated addition of EDCCl demonstrates the complete reversibility of... 

In drug discovery, we often avoid elevated temperatures because polar organic molecules tend to be thermally labile. Over the modest ranges used, temperature usually has little effect on retention. However, it has been observed that subtle changes in temperature can dramatically affect selectivity or relative retention. It is not uncommon for closely related compounds to show very different responses to 5-10°C changes in temperature. At 35°C, three tricyclic antidepressants coeluted, but at 40 °C, they were baseline separated (33). 

When this reaction was followed by GCMS, the tricyclic furan 205 was the major product observed the facile hydrolysis to butenolide 206 occurred during workup. The lability of 205 to hydrolysis is in marked contrast to the inert nature of the methyl ester 201 to acid-catalyzed conversion to the corresponding butenolide. 

It is remarkable that the two diastereomeric salts of the bisulfite adduct can be separated with phenylethylamine. After being liberated, the less stable bicycle is converted directly with excellent regio- and diastereoselectivity via an exo-bromonium ion [231] into the sUyl-protected bromohydrin. The tricyclic ketone is then generated with potassium t-butoxide the lability of this intermediate requires that it is used for the next reaction step as crude material. 

An attempted synthesis of 3-carboxymethyl quinuclidine-2-carboxylic acid anhydride in the presence of acetic anhydride and sodium acetate yielded unexpectedly a tricyclic /8-diketone (XVIII) [94]. The latter in the course of interaction with substances having a labile hydrogen atom (water, alcohols, amines) opened readily to form derivatives of 2-acetvlquinuclidine-3-acetic acid [94]. 

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