Stereoselective synthesis of alcohols, XXIII. Transfer of chirality on addition of (α‐chloroallyl)boronates to aldehydes

Abstract

The preparation of the (u-chloroally1)boronate 4 of 92% e.e. is described. Its addition to achiral aldehydes resulted in the homoallyl alcohols 6 of 82-92% e.e. Cooperative diastereoface selectivity on addition of ent-4 to isopropylideoeglyceraldehyde (22) gave the product 23 of high diastereomeric purity. Reagent control of stereoselectivity on addition of 4 to 22 resulted in 25 of 77% diastereomeric purity. Stere-lektive Synthese von Alkoholen, XXIII ') Chkalitiitsiibertragung bei der Addition von (a-Chlorallyl)boronsiureestern an AldehydeDie Darstellung des (a-Chlorally1)boronslureesters 4 mit 92% e.e. wird beschrieben. Seine Addition an achirale Aldehyde ergab die Homoallylalkohole 6 mit 82-92% e.e. Bei der Addition von ent-4 an Isopropylidenglycerinaldehyd (22) fiihrte die kooperative Diastereoseitendifferenzierung zum Produkt 23 hoher Diastereomerenreinheit. In der Reaktion von 4 mit 22 ergab die Stereokontrolle durch das Reagenz den Alkohol25 mit einer Diastereomerenreinheit von 77%.In the field of asymmetric syntheses the addition of chiral organometallic reagents to aldehydes and prochiral ketones has been under active investigation during the last decade2). Typical examples for such reagents are the allylboron compounds 1 having chiral residues on boron 3,4). Their addition to aldehydes leads to the homoallyl alcohols 3, a reaction in which the extent of asymmetric induction has been constantly improved, now frequently reaching and in some cases exceeding the 90% e.e. level9.The addition of the allylboron compounds 1 to aldehydes proceeds via cyclic six-membered transition states 2. In the reactions mentioned above asymmetric induction resulted from chiral control elements which were affixed to the periphery 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986

Rhodium catalysed dehydrogenative borylation of alkenes: Vinylboronates via C–H activation

“…6 They can be prepared by uncatalysed 7 or metal catalysed 8 hydroboration of alkynes, eqn (1). Recently, VBEs have been synthesised by Pd-catalysed cross-coupling of alkenyl halides or triflates with B 2 pin 2 , 9 eqn (2), by reaction of 1-halo-1-lithioalkenes and HBpin at −110 • C, 10 eqn (3), by Pt-catalysed 1,2-diboration of alkynes, 11 eqn (4), by Pd-catalysed diboration of methylenecyclopropanes, 12 eqn (5) and by Pd-catalysed borylsilylation or borylstannylation of 1,2-dienes, 13 eqn (6). Other interesting procedures for the formation of VBEs include Miyaura's unusual trans-hydroboration of alkynes, 14 presumably taking place via a vinylidene intermediate, eqn (7), the Ru-catalysed olefin cross-metathesis of vinyl boronates and alkenes, 15 eqn (8), catalytic boryl group transfer from a VBE to an alkene, 16 eqn (9), and the enyne cross metathesis reaction between alkynylboronates and terminal alkenes, 17 eqn (10).…”

Indium(I)‐Catalyzed Asymmetric Allylation, Crotylation, and α‐Chloroallylation of Hydrazones with Rare Constitutional and High Configurational Selectivities

“…Chemie catalyst with g selectivity to electrophiles. [25] Remarkably, the present asymmetric In I catalysis proved to be compatible with the reactive allylic CÀCl bond of rac-7, and almost exclusive a selectivity was observed; [22] a-adducts 8 were formed in good yields with excellent anti/syn ratios [15] (up to 99:1) and enantiomeric ratios of up to 93:7. These reactions represent rare examples of the catalytic formation of stereogenic centers bearing a chlorine atom with high asymmetric induction, which may lead to new disconnection approaches in the total synthesis of chlorinated natural products.…”

Synthesis and properties of 1-(3′-dihydroxyboryl-2′,3′-dideoxyribosyl)pyrimidines

“…Several analogous displacements of other diols by pinanediol have been reported previously. [21][22][23] The rigid geometry of pinanediol minimizes entropy loss in formation of its cyclic esters with boron, and the displacement of DICHED is further favoured by its precipitation from the reaction mixture.…”