Analogs convergent synthesis

The intramolecular Diels-Alder reaction of an appropriately substituted tetraene that bears the entire latent carbon framework and functional group substitution of himbacine has to be mentioned as the key step of this synthesis. It allows an efficient construction of the tricyclic ring system. In conclusion, this total synthesis provides a highly convergent synthesis of (+)-himbacine in about 10 % overall yield and also establishes a practical route to analogs. 

It was mentioned that oxidation by DDO allows the clean conversion of secondary alcohols into carbonyls under mild conditions. In this transformation the dioxiranes rank high with respect to transition-metal oxidants because of their efficiency, superior versatility, and ease of operations. Based on kinetic data and the application of reaction probes, the oxidation proceeds via a substantially concerted O-insertion by the dioxirane into the C-H bond alpha to the OH functionality generating a ge/w-diol C(0H)2, hence the carbonyl. As shown by the example in eq 36, remarkable chemoselectivity is achieved in the oxidation of epoxy alcohols in that the corresponding epoxy ketones are formed in high yield, while the epoxy functionality remains untouched. The epoxy ketone in eq 36 is a key intermediate in the convergent synthesis of active lQ ,25-dihydroxyvitainin D3 analogs. ... 

The synthesis of a novel cyclopropyl analog of arachidonic acid [7] via a convergent synthesis that employed methyl (lR,25)-2-formylcyclopropane-carboxylate in conjunction with the ylide from (3Z,6Z)-pentadeca-3,6-dienyl(triphenyl)-phosphonium iodide was reported (62). A new approach to cyclopropene fatty acids has been developed for the synthesis of methyl sterculate [8] and methyl 2-hydroxy-sterculate this involves the 1,2-deiodination of 1,2-diiodocyclopropanes with butyllithium at low temperature (63). The synthesis of deuterated cyclopropene fatty esters structurally related to palmitic and myristic acids has been reported (64). 

The convergent synthesis of dinotefiiran, the third-generation neonicotinoid from Mitsui Chemicals, applies a strategy analogous to clothianidin, but starts from nitroguanidine. Sequential transformations, first with methylamine and then with a mixture of methylamine and formaldehyde in water, form a hexahy-drotriazine. This is alkylated with activated racemic 3-(hydroxymethyl)tetrahy-drofuran acid hydrolysis then gives the active compound. [139]... 

Recently, De Meo reported the application of the SBox approach to stereoselective a-sialylation and to the convergent synthesis of a GM3 analog (74). In the latter synthesis, selective activation of the SBox moiety of the sialosyl donor over the S-ethyl moiety of the galactosyl acceptor was conveniently achieved in the presence of AgOTf The obtained disaccharide was used in subsequent coupling directly to afford the desired GM3 trisaccharide sequence in good overall yield. 

The synthesis and isolation of many of these receptors proved to be quite tedious, however, although occasionally convergent strategies could be used. We therefore looked for an alternative way to build up such structures and decided to make use of self-assembly processes of metal complexes [4] to build up self assembled oligo(BINOL) analogs [5], (How similar metal complexes can be used to stabilize peptide microstructures is discussed in Chapter 1.3.)... 

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