Double Annulation Route to Highly Substituted and Functionalized Trans-Fused Bicyclic Compounds

Asymmetric Catalytic Double Michael Additions for the Synthesis of Spirooxindoles

Asymmetric cascade double Michael additions to construct 2'-substituted 3,3'-spirooxindoles by using a chiral guanidine organocatalyst has been developed. A series of spirooxindole derivatives containing dihydrofuran or pyrrolidine subunits were obtained with good to excellent diastereo- and enantioselectivities. The method showed great tolerance of a number of aromatic and aliphatic alkynones. The strategy gave access to the asymmetric synthesis of (-)-salacin for the first time.

Functionalized cis- and trans-fused bicyclic alpha-amino acids via stereoselective double annulation and dequaternization reactions

Fused bicyclic alpha-amino acids can be prepared by a double Michael reaction of p-anisyl ethynyl ketone and a tethered diacid, cyclization via hydrogenation or hydration of a CN group, and oxidation of the p-anisyl group. The substitution level of the alpha-amino acids can be adjusted by decyanation or decarboethoxylation of the intermediates. Bicyclic alpha-amino acids prepared in this way include cis- and trans-perhydroisoquinoline-3-carboxylic acids and cis-perhydro-2-pyrindine-3-carboxylic acids of various substitutions and oxidation levels. The bicyclic alpha-amino acids may be regarded as functionalized and conformationally restricted analogues of proline, pipecolic acid, 2-aminoadipic acid, or glutamic acid.

Trimethylsilylethynyl ketones as surrogates for ethynyl ketones in the double Michael reaction

Trimethylsilylethynyl ketones can be desilylated in the presence of a tethered carbon diacid and induced to undergo a double Michael reaction in situ. The trimethylsilylethynyl ketones can serve as surrogates of ethynyl ketones that are difficult to prepare or isolate.

Short total syntheses of both the putative and actual structures of the clerodane diterpenoid (+/-)-sacacarin by double annulation

[reaction: see text] The putative structure of the naturally occurring clerodane diterpenoid (+/-)-sacacarin has been prepared in only 10 steps, six of which are C-C bond-forming steps, in a chemo-, regio-, and diastereoselective manner. The key part of the synthesis is the double annulation (double Michael, Pinner, and Dieckmann reaction) of a tethered carbon diacid and 3-butyn-2-one. A corrected structure for sacacarin is proposed, and the structure is proven by synthesis.

A heterocycle-forming double michael reaction. [5 + 1] annulation route to highly substituted and functionalized piperidines

[reaction: see text]. Nitrogen-containing tethered diacids, easily prepared by reductive alkylation of diethyl aminomalonate or ethyl cyanoglycinate, undergo double Michael reactions with 3-butyn-2-one to give highly functionalized and substituted piperidines (pipecolic acid derivatives) with surprisingly high stereoselectivity. The heterocyclic double Michael adducts can be induced to undergo further cyclizations to give a variety of azabicyclic and diazabicyclic compounds.

beta-Siloxy unsaturated nitriles: stereoselective cyclizations to cis- and trans-decalins

[formula: see text] beta-Siloxy unsaturated nitriles are excellent precursors to enolate and nitrile anions that cyclize to cis- and trans-decalins, respectively. The stereoelectronic requirements of endocyclic enolates and exocyclic nitrile anions are complementary, providing cis- and trans-decalins from a common intermediate. This cyclization allows the synthesis of diastereomeric cis- and trans-decalins containing a contiguous array of quaternary-tertiary-quaternary stereocenters.