Pd-catalyzed cyclization of 1,5- and 1,6-allenynes and 1,5-enallenes with bis(pinacolato)diboron affords synthetically useful allylboronates and alkylboronates under smooth conditions in a formal hydroborylative carbocyclization reaction. One C-C and one C-B bond are formed in a single operation. The reaction outcome implies that different mechanisms operate for the reactions of allenynes and enallenes, respectively, the actual pathway depending on the relative reactivity of the alkyne or the alkene versus the allene moiety. The cyclized boronates obtained can be functionalized by oxidation or allylation reaction with aldehydes.

Reaction of a variety of 1,7-enynes with bis(pinacolato) diboron catalysed by Pd bis(trifluoroacetate) affords homoallylic and allylic boronates containing a six membered carbo- or heterocycle, by formation of C-C and C-B bonds.

Reaction of a variety of dienynes with bis(pinacolato)diboron catalysed by Pd bis(trifluoroacetate) affords allylic boronates containing five or six membered carbo- or heterocycles, by concomitant formation of one C-C and one C-B bonds. Resulting allylboronates can be employed for a variety of subsequent transformations.

Pd-Catalyzed Borylative Cyclization of Allenynes and Enallenes. -The reaction leads to the major formation of endo-five-membered boronates from 1,5-and both endo-and exo-six-membered boronates from 1,6-allenynes. One C-C and one C-B bond are constructed in a single operation. The reaction is also applied to enallenes (XVII) and (XXI) to afford mixtures of alkyl and allylboronates in moderate yields. Some functionalizations of (IIIa) are demonstrated. -(PARDO-RODRIGUEZ, V.; MARCO-MARTINEZ, J.; BUNUEL, E.; CARDENAS*, D.

The cyclization of enynes (I) with dipinacolyl hypodiborate (II) leads to desired cyclic boronate derivatives (III), which can be oxidized to alcohols, e.g. compound (IV).