Intramolecular cross-coupling

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

Scheme 16 Construction of a nine-membered cyclic ether with a (Z,Z)-1,3-diene unit by sequential RCM and silicon-assisted intramolecular cross coupling in Denmark s synthesis of brasilenyne (85) [65]...

Chromans have been obtained by the Pd-catalysed intramolecular cross coupling reaction involving aryl halides containing an ortto-hydroxyalkyl substituent <96JA10333>. 

C-C bond formation can be favored over /3-hydride elimination by changing the nature of the catalyst. Hence, cyclizations can be mediated by iridium carbene complexes resulting from a formal intramolecular cross-coupling of the alkene with an. s -C-H bond (Equation (40)). 

Intramolecular cross-coupling can also be carried out as illustrated in the ring closure of Eq. 6 catalyzed by a nickel complex (L = l,2-bis-(diisopropyl phosphino)benzene) [25] ... 

Palladium-catalyzed intramolecular cross-coupling reaction of bis-aryl halides using ditin reagents. 

Primary alkylboranes derived by hydroboration of terminal alkenes with 9-BBN-H are coupled with aryl and alkenyl triflates and halides under properly selected conditions. The reaction proceeds smoothly without elimination of /1-hydrogen using PdCTklppf) or Pd(Ph3P)4 and K3PO4 in dioxane or DMF [132]. The intramolecular cross-coupling of the alkenyl triflate with the alkylborane in 292, prepared by in situ hydroboration of the double bond in 291 with 9-BBN-H, is applied to the annulation to... 

The Cp2TiCl/H20 combination can also be used for the chemoselective reduction of aromatic ketones. The reaction discriminates between ketones and alkenes, between ketones and esters and, remarkably, between conjugated and non-conjugated ketones [80]. There is strong evidence that this reduction proceeds via ketyl-type radicals, which are finally reduced by H-atom transfer from 42 [81]. Under dry conditions, titanium-promoted ketyl radicals from aromatic ketones can be used for intermolecular and intramolecular cross-coupling of ketones [82], Thus, depending on whether water is added or not, complementary and versatile synthetic procedure protocols are available. 

Scheme 14 A domino of twofold palladium-catalyzed allylation and reductive intramolecular cross-coupling reaction with subsequent cycloaddition [65]...

Scheme 21 Access to tricyclic isoxazolidines by an inter-intramolecular cross-coupling-cydoaddition cascade [81]...

Scheme 29 Inter-intramolecular cross couplings yielding 1,3,5-hexatrienes [105,107]...

The tentative mechanism suggests that the Pd-catalyzed metallation re-gioselectively substitutes triflate by tin (Scheme 68). Then, the intramolecular cross-coupling takes over to conclude the sequence with a reductive elimination resulting in the cyclization product 176. 

Intramolecular Cross-coupling of Enol Triflates with Organoboron... 

Intramolecular cross-coupling of enol triflates with organoboron... 

The intramolecular cross-coupling proceeds especially smoothly when the cyclization results in the fonnation of either five- or six-membered rings [139, 152, 153]. The hydroboration of the terminal double bond with 9-BBN is faster than that of the halogenated double bond relative rates are 196 (2-methyl-1-pentene), 100 (1-hexene), and... 

Good yields are achieved for five- and six-membered ring cyclizations by the intramolecular cross-coupling reaction of haloalkenes [139, 152], but the scope of reaction is still limited by the availability of the haloalkenes, particularly because of the absence of a simple method for preparing cyclic haloalkenes from ketone precursors. The ready availability of triflates from carbonyl compounds now offers a valuable tool for the annulation of ketones (Scheme 2-56) [160]. 

Equation 12.59 shows an intramolecular cross-coupling combined with a carbonylation, which was used in the synthesis of ( )-ep/-jatrophone (47), a diter-pene that possesses antitumor activity.126 Early in investigations on the reactivity... 

APPLICATION OF SILICON-ASSISTED INTRAMOLECULAR CROSS-COUPLING IN TOTAL SYNTHESIS OF (+)-BRASILENYNE... 

D. Formation of the Oxonin Core Sequential Ring-Closing Metathesis/Silicon-Assisted Intramolecular Cross-Coupling... 

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