1.3- dienyl-boronate

Different studies were carried out to develop diastereocontrolled versions of these Diels-Alder reactions. Better results were obtained when an optically pure diol was used as chiral director. The tandem reaction involving a 1,3-dienylboronate derived from tartrate esters proceeded with 70% enantiomeric excess (Scheme 9.35) [76]. The hetero-Diels-Alder reaction of enantiomerically pure (-t)-pinanediol 1,3-dienyl-boronate with an azo dienophile gave the J -configured endo cycloadduct as the single stereoisomer [77]. 

The hydroboration of enynes yields either of 1,4-addition and 1,2-addition products, the ratio of which dramatically changes with the phosphine ligand as well as the molar ratio of the ligand to the palladium (Scheme 1-8) [46-51], (P)-1,3-Dienyl-boronate (24) is selectively obtained in the presence of a chelating bisphosphine such as dppf and dppe. On the other hand, a combination of Pd2(dba)3 with Ph2PCsFs (1-2 equiv. per palladium) yields allenylboronate (23) as the major product. Thus, a double coordination of two C-C unsaturated bonds of enyne to a coordinate unsaturated catalyst affords 1,4-addition product On the other hand, a monocoordination of an acetylenic triple bond to a rhodium(I)/bisphosphine complex leads to 24. Thus, asymmetric hydroboration of l-buten-3-yne giving (R)-allenyl-boronate with 61% ee is carried out by using a chiral monophosphine (S)-(-)-MeO-MOP (MeO-MOP=2-diphenylphosphino-2 -methoxy-l,T-binaphthyl) [52],... 

One last example of the aza-Diels-Alder reaction finishes this section. The diene 215 is a curious hybrid of a dienyl boronate and the sort of aza-diene we met in chapter 33 and is easily prepared by hydroboration of a suitable functionalised acetylene 213. 

The cyclic allylboronic acids 81 provided the trisubstituted (Z)-olefins 82 when treated with alkaline hydrogen peroxide (Equation 2). If, instead of boracycles 81, the cyclic dienylic boronic acids 83 are used in the previous reaction, the stereodefined, trisubstituted dienylic carbinols 84 are formed (Equation 3) <2002AGE152>. 

Diels-Alder cycloaddition of the dienylic boronic acid 86 provided stereoselective access to the tetracyclic and tricyclic heterocycles 87 (de > 13 1) and 88 (de >20 1) (Scheme 8) <2002AGE152>. 

P-Substituted vinylboronic esters were isolated in fair to high yields from the coupling under classical Heck conditions of vinylBhg with (hetero)aryl iodides and bromides (Table 3.1, entries 1-3). A dienyl boronic ester was obtained by coupling of vinylBhg with a vinyl iodide derived from phenylgly-cine (entry 4). The preparation of a styryl boronic ester with a sulfonamide moiety is described in a patent (entry 5) this product was later used in a Suzuki-Miyaura reaction. ... 

Cycloadditions and Other Additions to Alkenyl-, Alkynyl- and Dienyl Boronic Esters... 

Due to their great versatUity, boron-substituted dienophiles and dienes have emerged as attractive building blocks in Diels-Alder reactions [47]. In this section, we review the most important results related to the [4-i-2] cycloadditions involving alkenyl, alkynyl and dienyl boronic esters and some of their derivatives. 

The application of ( )-55b to the Heck reaction with vinylboronate 61 gave (l ,3 )-(4-fluoro-l,3-dienyl)boronate 62 stereoselectively ((1 ,3 ) = 96%). The resulting (fluorodienyl)boronate 62 was used in the Suzuki-Miyaura coupling and fluorotriene 63 was obtained stereoselectively [90] (Scheme 28). 

Palladium catalyzed coupling reactions between halodienes and bis(pinacolato) diborane or hexamethylditin have been reported to yield the corresponding (lZ,3 )-l,3-dienyl boronate and stannane, respectively (Scheme 85) [180]. 

Dibromoborane-Dimethyl sulfide, 92 Dichloro(dimethylamino)borane, 120 Diisobutylaluminum hydride-Boron trifluoride etherate, 116 Diisopinocampheylborane, 117, 182 Diisopinocampheylmethoxyborane, 86 Dimesitylmethylborane, 8 Dimethoxy[l-trimethylsilyl-l,2-buta-dienyl]borane, 218 (R,R)- and (S,S)-frans-2,5-Dimethyl-borolanes, 119... 

Brown and co-workers developed a novel homoallenyl boronate reagent 169 based on diisopropyl tartrate for the stereoselective homoallenylation of aldehydes 170. The reagent 169 was prepared via homologation of the corresponding allenyl boronate or the alkylation of halomethyl boronate with allenyl Grignard similar to those reported in Scheme 26. The allyl boronate 169 upon reaction with aldehydes furnished the dienyl alcohols 172 with high ee (Scheme 28) <1996JOC100>. 

Isochromen-3-yl trifluoromethanesulfonate 162, formed from isochroman-3-one, can undergo a palladium-catalyzed cross-coupling reaction with the boronate 163 to afford ( )-3-(l-ethoxybuta-l,3-dienyl)-177-isochromene in moderate yield (Scheme 52) <2005T3429>. 

Other functional groups containing group III-A elements have also been employed as sources of fluorinatcd compounds. Thus, 5-fluorocyclopenta-l,3-diene(21)can be obtained by reaction of (cyclopenta-2,4-dienyl)thalium with l-(chloromethyl)-4-lluoro-1,4-diazoniabicyclo[2.2.2]oc-tane bis(tetrafliioroboratc) in acetonitrile. The reaction of arylthalium(III) difluorides with boron trifluoride also yields the corresponding aryl fluorides (45-71... 

Anions formed from group 6 and manganese Fischer carbene complexes undergo aldol condensations with aldehydes and ketones. Allylic carbenes exclusively react in the y position with aldehydes affording dienyl-substituted carbenes. For alkoxy-substituted carbenes, the presence of an excess Lewis acid see Lewis Acids Bases), such as boron trifluoride etherate, titanium tetrachloride, or tin tetrachloride is required for the reaction to proceed in reasonable yield. The initial aldol product can be isolated without elimination (Scheme 12). ... 

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