Olefins diene natural product synthesis

The [2+2]-photocycloaddition of carbonyl groups with olefins (Paterno-Buchi reaction) is one of the oldest known photochemical reactions and has become increasingly important for the synthesis of complex molecules. Existing reviews have summarized the mechanistic considerations and defined the scope and limitations of this photocycloaddition73. Although this reaction likely proceeds via initial excitation of the carbonyl compound and not the excited state of the diene, the many examples of this reaction in natural product synthesis justify inclusion in this chapter. 

Undheim and co-workers employed their olefin metathesis strategy for the synthesis of five- and six-membered ring spirocyclic carbocycles to prepare seven-membered ring spirocyclic carbocycles for use as templates in natural product synthesis. Reaction of diene 295 with 2 mol % of 3 furnished the corresponding spirocycle 296 in only 60% yield. However when diene 297 was reacted under similar conditions, the desired spirocycle 298 was obtained in 90% yield. Although no specific reason is given for the lower yield of 296, it is possible that conformational constraints and/or sterics may have played a role. 

RCM of 1,8-dienes constitutes an efficient access to cycloheptenes since di-, tri-, and tetrasubstituted olefins could be elaborated in good yields with catalyst loading as low as 1 mol%. In this context, the highly demanding field of natural product synthesis constitutes an efficient test for the development of more active and... 

RCM of dienes to cycloalkenes provides a useful method for the syntheses of carbo- and heterocycles and thus has been proved to be extremely effective in total synthesis of various natural products. Usually, however, mixtures of (E)- and (Z)-olefms result. In contrast, ring-closing alkyne metathesis provides a reliable route for synthesis of both (E)- and (Z)-macrocycloalkenes in a stereoslective manner taking advantage of stereoselective partial reduction of resulting cycloalkynes. A Lindlar reduction gives (Z)-cycloalkenes, whereas a hydroboration/ protonation sequence afford ( )-cycloalkenes (Equation (23)). Recently, Trost reported an alternative procedure for the synthesis of (E)-olefins from alkynes through hydrosilylation by a ruthenium catalyst. This procedure converts cycloalkyne 130, for example, to vinylsilane 131 and then to (E)-cycloalkene 132 in a stereoselective manner (Scheme 46)7 ... 

With regard to the synthesis of the oligo-cyclo-propane natural product FR-900848 (1) multiple and consecutive cyclopropanation reactions using zinc carbenoids have been applied. Thus, in the total synthesis of 1 by Barrett et al. the Furu-kawa-procedure was used for the conversion of 52 into the biscyclopropane 53 (Scheme 11). [37] After bidirectional elongation of the molecule, another double cyclopropanation of diene 54 using Charette s catalyst gave tetracyclopro-pane 55 in 93 % yield as one stereoisomer only. Finally, the olefin 56 is cyclopropanated at -40 °C to yield the desired pentacyclopropane alcohol 57. Thus, all five cyclopropane rings of... 

The absolute configuration of radiosumin, a novel potent trypsin inhibitory dipeptide, was determined by T. Shioiri and co-workers by carrying out the first enantioselective total synthesis of the natural product. The s-trans 1,3-diene in one of the key synthetic intermediates was installed by the Corey-Winter olefination using the Corey-Hopkins reagent (1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine). 

The third and fourth examples involve intramolecular oxidation of olefins with a protected alcohol and with a carboxylic acid. Cleavage of a silyl protected alcohol, followed by oxidative C-0 bond formation at the p-position of an acrylate group was conducted at the late stage of the synthesis of the alkaloid alstophylline. Intramolecular 1,4-oxidations of dienes have been used in the synthesis of a number of natural products. For example, the intramolecular oxidation shown in Scheme 16.30 led to the precursor to Paeonilactone... 

---