Selective hydroboration of conjugated diynes with dialkylboranes. A convenient route to conjugated cis-enynes, .alpha.,.beta.-acetylenic ketones, and cis,cis-dienes

Abstract

The monohydroborations of dodeca-5,7-diyne, 2,7-dimethylocta-3,5-diyne, and 2,2,7,7-tetramethylocta-3,5-diyne with disiamylborane [bis(3-methyl-2-butyl)borane] proceed to place the boron preferentially at the internal positions of the diyne system. The organoboron intermediates upon protonolysis with acetic acid give the corresponding cw-enynes in high yields. Oxidation of the monohydroboration products with alkaline hydrogen peroxide affords the corresponding ,ß-acetylenic ketones in better than 70% yields. Dihydroboration of dodeca-5,7-diyne, 2,7-dimethylocta-3,5-diyne, and 2-methyldodeca-3,5-diyne with dicyclohexylborane followed by protonolysis produces the corresponding dr,di-dienes. For hindered diynes such as 2,2,7,7-tetramethylocta-3,5diyne, however, reduction to the diene has to be carried out stepwise. Thus, the diyne is first converted to the enyne via the hydroboration-protonolysis reaction. Subsequent hydroboration of the di-enyne followed by protonolysis with acetic acid affords dr,dj-2,2,7,7-tetramethylocta-3,5-diene. The hydroboration of conjugated dienes has been the subject of numerous investigations and has resulted in new routes to a large number of acyclic and cyclic organoboranes which undergo versatile chemical transformations.2 The hydroboration of conjugated diynes and the chemistry of the resultant organoboranes, on the other hand, has remained essentially unexplored.

Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation–Pd-catalyzed cross-coupling

“…Critical comparision of the synthesis of (all-E)-trienoic ester (23) by three mutually complementary HWE olefination routes.…”

“…(a) Alkyne elementometalation-Pd-catalyzed Negishi coupling protocol. The alkyne elementometalation-Pd-catalyzed Negishi coupling protocol shown in Scheme 5 has provided uniformly satisfactory routes to all four stereoisomers of ethyl (4E)-trideca-2,4,6-trienoates (23)(24)(25)(26) in three steps without generating any detectable amounts of stereoisomers or any other isomers. We therefore opted for reporting to the same strategy for the syntheses of 27-30 as well by making use of both (E)-and (Z)-3-decen-1-ynes (31 and 32, respectively) prepared in two steps as shown in Scheme 5.…”

“…In addition to (2Z,4E)-dienoic esters, some (2Z,4E,6E)-and (2Z,4E,6Z)-trienoic esters have been prepared in ≥98% selectivity by a newly devised Pd-catalyzed alkenylation-SG olefination tandem process. As models for conjugated higher oligoenoic esters, all eight stereoisomers for ethyl trideca-2,4,6-trienoate (23)(24)(25)(26)(27)(28)(29)(30) have been prepared in ≥98% overall selectivity.…”

“…2. One of the most notable advances made in this study is the synthesis of all eight stereoisomers of ethyl trideca-2,4,6-trienoate (23)(24)(25)(26)(27)(28)(29)(30) in good yields and ≥98% selectivity by using the Negishi or Suzuki version of Pd-catalyzed alkenylation. It is anticipated and hoped that the study on triene syntheses reported herein will form a reliable and useful foundation for its applications and extensions in selective syntheses of a variety of conjugated trienes and higher oligoenes as well.…”

Stereoselective synthesis of some isomers of dodecadien-1-ol: Compounds related to the pine moth sex pheromone.

“…After the synthesis of 1-bromohexyne (3) from 1-hexyne using the reported reaction,3) a Chodkiewics Cadiot reaction3) between this 1-bromoacetylene (3) and the above acetylene (2) gave 5,7-dodecadiyn-1-ol THP ether (4) Scheme 4. Synthesis of (5E,lE)-5,7-Dodeciidien-l-oL The expected geometries of these dienols were supported by IR absorption-bands at 720 and 980 cm"1 (see Experimental).…”