Greenspoon performed and recorded with Linda Ronstadt, Eric Clapton, Jimi Hendrix, America, The Beach Boys, Beck, Bogert & Appice, Nils Lofgren, Lowell George, Kim Fowley, Donovan, Buddy Miles, Stephen Stills, Jeff Beck, Chris Hillman, Steve Cropper, Duck Dunn, James Burton, Hal Blaine, Leon Russell, The Wrecking Crew, Osibisa, Shaun Cassidy, Cheech & Chong, and Redbone.

Greenspoon attended Beverly Hills High School along with Richard Dreyfuss, Bonnie Franklin, his childhood friends producer, Michael Lloyd and drummer, songwriter, singer Art Guy.

His bands held residence at The Trip, Stratford on Sunset (now The House Of Blues), Brave New World, Bidos Litos, Ciros, and The Whiskey.

In late 1966, Greenspoon moved to Denver, Colorado with members of The West Coast Pop Art Experimental Band and formed the group Superband.

Greenspoon served as an Entertainment and Media Consultant with the Murry-Wood Foundation and composed original music for the movies Fragment, produced by Lloyd Levin, United 93, Hellboy, Watchmen, Field of Dreams, Predator, and Die Hard.