Ethyl sidechain

The total synthesis of Stemona alkaloid (-)-tuberostemonine was accomplished by P. Wipf. Late in the synthesis, the introduction of an ethyl sidechain was required. This could be achieved in a novel four-step sequence. First, the allyl sidechain was introduced by the Keck radical allylation. To this end, the secondary alkyl phenylselenide substrate was treated with allyltriphenyltin in the presence of catalytic amounts of AIBN. This was followed by the introduction of a methyl group onto the lactone moiety. The allyl group then was transformed into the desired ethyl group as follows the terminal double bond was isomerized to the internal double bond by the method of R. Roy. This was followed by ethylene cross metathesis and catalytic hydrogenation to provide the desired ethyl sidechain. 

In traditional synthetic organic chemistry, the Wittig reaction plays an important role in carbon-carbon bond extension from the carbonyl group. CM is an attractive alternative for carbon-carbon extension from a terminal alkene. In fact, a pyrroh-dine ring of anthramycin derivative 55 has been constructed by RCM of 52, and the sidechain has been extended by CM of terminal alkene of 54 with ethyl acrylate. " In the CM, ruthenium carbene complex Ij, reported by Blechert, gives a good result since the ligand of the catalyst easily dissociated from the ruthenium metal at room temperature ... 

The achiral ethyl ketone 218 (Scheme 9-59) has been used in the synthesis of epothilone B [79]. Here the asymmetric induction comes from aldehyde 219 alone and, at very low temperature, is surprisingly high (85%ds). It appears the unsaturated sidechain of the aldehyde plays an important role, as aldol addition to saturated aldehyde 220 led to an unselective reaction. 

Fig. 4 Molecular structure of diblock copolymers and side-chain modified lipopolymers whose pressure-area isotherms are presented in Figs. 6 and 7, respectively. Diblock copolymers are poly(2-n-nonyl)-poly(2-methyl or 2-ethyl-2-oxazoline) (NxEy and NxMj,), where x and y denote the block sizes of the hydrophobic nonyl and hydrophilic oxazoline blocks. Side-chain modified lipopolymers, which contain short oligo-EG sidechains in each monomer of the lipopolymer to create a bottle-brush-like structure, are di-octadecanoyl-glycerol 2-(3 -methoxymonoethylene glycol)propyl-2-oxazoline (DiCigMEGOxn) and di-octadecanoyl-glycerol 2-(3 -methoxytiiethyleneglycol)propyl-2-oxazoline (DiCisTEGOxn) (adapted from [7,8])...

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