An efficient cross-addition reaction of dienes with aldehydes was developed by using RuHCl(CO)(PPh3)3 as a catalyst to give a wide variety of beta,gamma-unsaturated ketones, where a pi-allylruthenium species, derived from hydroruthenation of diene, may be involved as a key intermediate.

Lactonization of dialdehydes and keto aldehydes was effectively catalyzed by RuHCl(CO)(PPh(3))(3). A cascade lactonization sequence accompanied by cross-coupling with enones was also attained.

It all adds up: Straightforward access to 2‐alkyl‐substituted 1,3‐diketones is provided by a regioselective addition of aldehydes to enones catalyzed by the ruthenium hydride catalyst [RuHCl(CO)(PPh3)3] (see scheme). The reaction involves a hydrometalation of the enone to form a metal enolate, a cross‐aldol reaction to form an alkoxymetal species, and a subsequent β‐metal hydride elimination.

The title domino reactions were developed to directly provide tetrahydrofuro[3,4-c]isoxazole derivatives (5 and 9) in > or =90% ee from racemic alpha-hydroxynitrones (2 and 6), which were used in the concise asymmetric total synthesis of (-)-rosmarinecine .

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