Unsaturated compounds, synthesis with reagents

Unsaturated compounds, synthesis with alkenyl- and alkynylaluminum reagents, 32, 2... 

Convenient disconnection of the 1,5-dicarbonyl pattern results in the a,p unsaturated compound, enone, with a highly reactive C=C bond. Partners in the synthesis are neutral enone and a-carbanion of the second carbonylic reagent to complete the well-known Michael addition [22, 23]. Hence, the disconnection of the central bond in the 1,5-dicarbonyl pattern is denoted as the retro-Michael. 

The chemoselective oxidation of a saturated secondary alcohol in the presence of a saturated primary alcohol is possible with a number of reagents. N-Bromosuccinimide in an aqueous organic solvent has been used to carry out this type of selective oxidation and has found use in synthesis. The value of this reagent is exemplified by its use in the synthesis of isocyanopupukeanane and in work towards a total synthesis of gelsemine (equations (32) and (33) respectively). Clearly this reagent would not be compatible with all functional groups, given the well-known reactivity of N-bromosuccinimide towards unsaturated compounds. 

Corey found the reagent useful for the synthesis of half-esters of a,/3-unsaturated malonic esters. Isopropylidene malonate condenses readily with carbonyl compounds, even with the highly hindered mesitaldehyde (1). Thus the condensation of (I) and (2) was conducted in pyridine solution, and the product (3) on being refluxed with absolute ethanol and a trace of hydrogen chloride afforded ethyl hydrogen mesitylidene malonate (4). 

Other Unsaturated Compounds. - The dienals 13 (with D-xylo-, D-lyxo- and D-arahino-configurations) have been condensed with the phosphonate 14 to give the enone adducts 15 the intramolecular Diels-Alder reactions of these adducts are mentioned in Chapter 22. Treatment of the unsaturated lactone 16 with the Tebbe reagent has afforded 17 its conversion into a cyclooctene derivative is covered in Chapter 18. Exposure of the cyclic sulfate 18 to base has afforded a mixture of the exo- and endo-olefins 19 and 20, ° and a syn-selective dihydroxyla-tion of the 3,4-unsaturated pyranoside 21 generated predominantly the D-allo product. Synthesis of the branched-chain 5,6-ene 22 using standard methods, and its conversion into a cyclitol during the first total synthesis of (—)-tetracyc-line is mentioned in Chapter 22. 

This reaction was first reported by Schollkopf in 1979. It is a synthesis of an unnatural nonproteinogenic amino acid from the lithiated enolate equivalent of a simple amino acid (e.g., glycine, alanine and valine), which involves the diastereoselective alkylation of the lithiated bis-lactim ether of an amino acid with an electrophile or an Aldol Reaction or Michael Addition to an o ,jS-unsaturated molecule and subsequent acidic hydrolysis. Therefore, the intermediate of the bis-lactim ether prepared from corresponding amino acids is generally referred to as the Schollkopf bis-lactim ether, " Schollkopf chiral auxiliary, Schollkopf reagent, or Schollkopf bis-lactim ether chiral auxiliary. Likewise, the Schollkopf bis-lactim ether mediated synthesis of chiral nonproteinogenic amino acid is known as the Schollkopf bis-lactim ether method, Schollkopf bis-lactim method, or Schollkopf methodology. In addition, the reaction between a lithiated Schollkopf bis-lactim ether and an electrophile is termed as the Schollkopf alkylation, while the addition of such lithiated intermediate to an Q ,j8-unsaturated compound is referred to as the Schollkopf-type addition. ... 

---