REARRANGEMENT OF SUBSTITUTED ARYLOXYMETHYL CHROMONES AND MECHANISTIC INVESTIGATION SYNTHYSIS OF HYDROXYHOMOISOFLAVONES AND HOMOPTEROCARPANES

Abstract

The aromatic Claisen rearrangement has emerged as a very important newlinetool for stereoselective C-C bond formation. Many natural products and newlineheterocyclic compounds have been synthesized using chromones and newlinechromanones by applying variants of this rearrangement as a key step. So newlinefar, there are no reports on Claisen rearrangement involving the double bond newlineof the chromone ring as part of the allyl moiety. With these facts in mind, newlinechromone-3-ylmethyl aryl ethers and chromone-2-ylmethyl aryl ethers were newlinesynthesized and the rearrangement behavior under thermal and TFA newlineconditions has been studied. newlineNovel and serendipitous finding on the synthesis of 3,3-bis-(4-oxochromen- newline3-ylmethyl)-chroman-4-one (trimeric chromone), which was newlineencountered during the synthesis of chromone-3-ylmethyl aryl ethers via newlineBuchwald-Hartwig coupling of 3-hydroxymethylchromone with bromobenzene, newlineis described. newlineThe center core of this thesis deals with the Claisen rearrangement of newlinechromone-3-ylmethyl aryl ethers. Chromone-3-ylmethyl aryl ethers with one or newlineboth vacant ortho positions have been found to undergo a novel domino [1,3]- newline[1,3]-rearrangement to give 4 -hydroxyhomoisoflavones under thermal newlineconditions while the para-substituted ethers led to 2 -hydroxyhomoisoflavones newlineinvolving a O- to C-[1,3]-migration, instead of the expected Claisen newlinerearrangement. Whereas under TFA condition, chromone-3-ylmethyl aryl newlineethers have been found to undergo a facile ortho selective [1,3]-migration at newlinethe aryl moiety to give 2and#1048973;-hydroxyhomoisoflavones. newlineHomopterocarpanes, a non-natural product which are homolog to the newlinesecond largest natural products pterocarpanes have been synthesised using newlinethe 2 -hydroxyhomoisoflavones obtained from the TFA catalysed [1,3]- newlinerearrangement of chromene-3-ylmethyl aryl ethers.The synthesis of hitherto newlineunknown trans-homopterocarpanes has been disclosed for the first time by newlineBuchwald reaction of trans-3-(2-bromobenzy)-4-chromanols. newline