Tandem dienyne ring-closing metathesis of alkynyl silaketals for the formation of bicyclic siloxanes
摘要:
The tandem dienyne ring-closing metathesis of alkynyl silaketals containing two tethered olefins was achieved with second generation Grubbs NHC-ruthenium carbene complex to provide bicyclic siloxanes in good to excellent yield. Silaketals synthesized from homoallylic or bishomoallylic alcohols via base-catalyzed alcoholysis of trialkynylsilanes were well tolerated in the metathesis process and generated ring systems of various sizes. Removal of the silicon tether was achieved through protodesilylation with fluoride to afford stereochemically defined (1E,3Z)-dienes. (c) 2005 Elsevier B.V. All rights preserved.
hetero-Michael (DIHMA) reaction to alkynones was applied. The sequence allows for introduction of numerous substituents on the scaffold and for variation of stereochemistry. [5.5]-Spiroketals bearing an additional ketone were obtained in high overall yields. Further diversification was achieved by reduction of the ketone and reductive amination using polymer-supported borohydride, Grignard reaction and conversion
Stereoselective Synthesis of the Tetrahydropyran Core of Polycarvernoside A
作者:Conor S. Barry、Nick Bushby、John R. Harding、Christine L. Willis
DOI:10.1021/ol050840o
日期:2005.6.1
[reaction: see text] A concise and stereoselectivesynthesis of the tetrasubstituted tetrahydropyran core of polycavernoside A was achieved in 55% overall yield from 3-benzyloxypropanal. A stereoselective allyl transfer reaction was used in the synthesis of enol ether 18 followed by a TFA-mediated cyclization to create the three new asymmetric centers in the tetrahydropyran with complete stereocontrol in
New and Stereoselective Synthesis of 1,4-Disubstituted Buten-4-ols (Homoallylic Alcohol α-Adducts) from the Corresponding γ-Isomers (3,4-Disubstituted Buten-4-ols) via an Acid-Catalyzed Allyl-Transfer Reaction with Aldehydes
from aldehydes via the usual reaction with common allylic metals 1, were converted to the corresponding α-adducts 6 by an acid-catalyzed allyl-transfer reaction. In the allyl-transfer reaction, anti- and syn-γ-adducts 3 gave E- and Z-α-adducts 6, respectively, and the optical purity of the γ-adducts 3 was transferred to the α-adducts 6 with >98%ee. This suggests that the allyl-transfer reaction proceeds
Solid phase synthesis of a spiro[5.5]ketal library
作者:Stefan Sommer、Herbert Waldmann
DOI:10.1039/b511177c
日期:——
A spiro[5.5]ketal library embodying the core structure of numerous biologically active natural products was synthesized employing a double intramolecular hetero Michael reaction as a key transformation.
Convenient synthesis of highly optically active 2,3,4,6-tetrasubstituted tetrahydropyrans via Prins cyclization reaction (PCR) of optically active homoallylic alcohols with aldehydes
Prins cyclization reaction (PCR) of opticallyactive homoallylic alcohols, RaC*H(OH)CH2CHCHCH3 (1-substituted but-2-en-1-ol), with aldehydes (RbCHO) in the presence of an acid-catalyst (HX) affords (2-Rb,3-CH3,4-X,6-Ra)-tetrasubstituted tetrahydropyrans highly stereoselectively in good yields.
旋光性均烯醇R a C * H(OH)CH 2 CHCHCH 3(1-取代的丁-2-烯-1-醇)与醛(R b CHO)的Prins环化反应(PCR)酸催化剂(HX)以良好的产率高度立体选择性地提供(2-R b,3-CH 3,4 -X,6-R a)-四取代的四氢吡喃。