Total asymmetric synthesis of advanced polyketide fragments of apoptolidinone and rectricticin using new organic chemistry of sulfur dioxide

Under appropriate conditions sulfur dioxide reacts with 1,3-dienes in a hetero-Diels-Alder fashion. In the case of 1-alkoxy-1,3-dienes the 6-alkoxy-3,6-dihydro-1,2-oxathiin-2-oxides (sultines) so-obtained can be ionized in the presence of Lewis or protic acids. The zwitterionic intermediates can be trapped as electrophiles with enoxysilanes (oxyallylation) to generate substituted silyl alkenylsulfinates. The latter can then be reacted with TBAF and an electrophile to generate polyfunctional sulfones (one pot, four component syntheses). Alternatively, desilylation through silicon/palladium transmetallation, in the presence of a catalytic amount of Pd(OAc)2, leads to intermediate allylsulfinic acids, which, after retro-ene desulfitation, produce 4-alkoxyhept-6-en-2-one core, a valuable fragment in polyketide natural product synthesis. The first part of this work described the application of an asymmetric version of this new SO2 reaction cascade, hetero-Diels-Alder addition/oxyallylation/retro-ene desulfitation (Vogel's cascade), using enantiomerically enriched dienes. The synthesis of a variety of β-alkoxy ketones was realized with good α,β-syn selectivity, starting from different enoxysilanes, illustrating the versatility of the method. An iterative Vogel's cascade employing newly obtained fragments provided long-chain polypropionate fragments such as (-)-(4R,5R,6S,9S,10R,2E,11E)-4,6,10-trimethyl-5,9-bis-((1S)-1-phenylethoxy)-trideca-2,11-dien-7-one in a very short and efficient way. The synthetic potential of Vogel's cascade reaction was demonstrated by the short and elegant synthesis of the enantiomerically enriched polypropionate fragment (C16-C28) of apoptolidinone, aglycon of apoptolidin, a highly potent apoptosis inducing agent. In the second part of thesis the one pot polyfunctional sulfone synthesis, developed in our group was successfully combined with the aldol methodology of Paterson to reach an advanced polyketide fragment, a potential intermediate in the total synthesis of Restricticin. Finally, in the last part of this study, we have demonstrated that methallyl silylsulfinates, known as new reagents for alcohol silylation are very precious and efficient reagents for the silylation of phenols and carboxylic acids. Additionally, the chemoselectivity of these reagents on substrates containing different hydroxyl groups was demonstrated.