Function-Oriented Synthesis toward Peloruside A Analogues.

A convergent and rapid synthesis of original C2,C3-unsaturated, C11,C13-keto-enol macrocycles with a peloruside A skeleton has been developed. These original unsaturated macrocycles constitute valuable platforms to access peloruside A analogues with high diversity. The four-fragment strategy implemented features two aldol-type couplings with the central C12-C14 building block TES-diazoacetone and a late-stage ring-closing metathesis. Enantiopure analogue 18ab showed antiproliferative activity in the low micromolar range on NCI and MCF7 tumor cell lines.

TBAF-Triggered Aldol-Type Addition of α-Triethylsilyl-α-diazoacetone.

Aldol-type addition of α-triethylsilyl-α-diazoacetone was achieved under nucleophilic activation by tetrabutylammonium fluoride (TBAF). The use of a semistoichiometric amount of TBAF (protocol P1) provided the corresponding ß-hydroxy-α-diazoacetone as the sole product. Alternatively, the use of a catalytic amount of TBAF led to a mixture of ß-hydroxy- and ß-silyloxy-α-diazoacetone products, which was cleanly desilylated with Et3N·3HF (protocol P2). The weakly basic conditions employed tolerate a wide range of substrates and constitute a high-yielding, convenient complementary procedure to the low-temperature LDA-promoted aldol-type addition of diazoacetone.

Tandem Payne/Meinwald versus Meinwald rearrangements on the α-hydroxy- or α-silyloxy-spiro epoxide skeleton.

Under Lewis acid activation, the new α-hydroxy-spiro epoxide scaffold 1a underwent an original tandem Payne/Meinwald rearrangement affording the cyclopentyl hydroxymethylketone 6 in a stereospecific manner, while a Meinwald-type epoxide rearrangement occurred when the derived α-trimethylsilyloxy-spiro epoxide 2a was treated with MABR, yielding stereoselectively the cyclohexane carbaldehyde 9.

Novel use of N-benzoyl-N,O-acetals as N-acylimine equivalents in asymmetric heterocycloaddition: an extended enantioselective pathway to beta-benzamido aldehydes.

For the first time, easily available N-(alpha-methoxyalkyl)amides were successfully used as synthetic equivalents of N-acylimines in an asymmetric heterocycloaddition process. The facial-controlled formation of 6-alkoxydihydrooxazines was thus achieved by SnCl(4)-promoted heterocycloaddition of (R)-O-vinyl pantolactone. By simple acidic hydrolysis of the crude heteroadducts, new beta-aryl- and beta-alkyl-substituted benzamido aldehydes were thus obtained in good overall yields with high enantioselectivities.