Biomedical subjects
Publications and source records attributed to D L Clive.
Phosphinates 20a-35a give biaryls 20b-35b on heating with stannanes in the presence of AIBN. The process involves a radical ipso substitution on the migrating aryl ring.
Acetylenic alcohol 10 was converted successively into silane 11 and phenylseleno carbonate 14. On treatment with Ph3SnH, the latter underwent 5-exo-digonal radical cyclization, intramolecular hydrogen transfer, and 5-endo-trigonal cyclization, yielding 15. Conversion of the lactone into the lactol benzyl ether 17, carbon-silicon bond cleavage, and regeneration of the lactone carbonyl gave (+)-juruenolide C (1).
Radicals of type 1 undergo 5-exo diagonal cyclization, and the resulting vinyl radical abstracts hydrogen from silicon to afford a silicon-centered radical. This radical closes in a 5-endo trigonal manner to generate radicals of type 4, which are reduced (4 --> 5) by stannane, except when the starting acetylene carries a terminal trimethylstannyl group. In this case, radicals 4 expel trimethylstannyl radical to afford vinyl silanes 6. The stereochemical outcome of the radical cascade 1 --> 5 is controlled by the stereochemistry of the oxygen-bearing carbon in 1 (see starred atom). The sequence can be initiated by carbon-, alpha-substituted carbon-, oxyacyl-, and carbamoyl radicals and generates a silicon-containing ring fused onto a carbocycle or heterocycle. Numerous examples are described, as well as a number of transformations of the final cyclization products, especially their response to n-Bu(4)NF and to BF(3).OEt(2), reagents that cleave the newly formed carbon-silicon bond.
Glyoxylic acid diphenylhydrazone (2a) and the corresponding O-benzyloxime (2b) are easily esterified in high yield by beta-bromo alcohols. The resulting esters undergo radical cyclization to alpha-(2,2-diphenylhydrazino)- or alpha-[(phenylmethoxy)amino]lactones on treatment with tributyltin hydride. Esters for radical cyclization were also made using a beta-(phenylseleno) alcohol and an enol ether. Several derivatives of glyoxylic acid were evaluated, but none was as effective as 2a or 2b. The imine 28 was prepared by an indirect route; it undergoes radical cyclization with displacement of the nitrogen substituent (28 --> 30) so that an alpha-amino lactone can be generated by acid hydrolysis of the cyclization product.
Puraquinonic acid (1) was synthesized from 2,5-dimethoxybenzoic acid by way of isochroman 2 and the indanone derivative 3, a Nazarov cyclization being used to construct the five-membered ring.
The synthesis, in racemic form, of the insect juvenile hormone inhibitor brevioxime (1) is described, as well as exploratory studies that led to the related model compounds 14 and 15a. The route to 1 involves Ag(+)-mediated coupling of the amine derived from 20 with the beta-keto thioester 32. Acid treatment of the coupled product 33 led by acetal hydrolysis, cyclization, and desilylation to 34a,b, from which 1 was reached by oxidation and conversion into the oxime. In the synthesis of the amino component 20, a known, but unusual, reduction was used for converting a nitrile into an amine hydrochloride.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.